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authorLinus Torvalds <torvalds@linux-foundation.org>2018-06-06 18:39:49 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2018-06-06 18:39:49 -0700
commit1c8c5a9d38f607c0b6fd12c91cbe1a4418762a21 (patch)
treedcc97181d4d187252e0cc8fdf29d9b365fa3ffd0 /Documentation
parent285767604576148fc1be7fcd112e4a90eb0d6ad2 (diff)
parent7170e6045a6a8b33f4fa5753589dc77b16198e2d (diff)
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Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next
Pull networking updates from David Miller: 1) Add Maglev hashing scheduler to IPVS, from Inju Song. 2) Lots of new TC subsystem tests from Roman Mashak. 3) Add TCP zero copy receive and fix delayed acks and autotuning with SO_RCVLOWAT, from Eric Dumazet. 4) Add XDP_REDIRECT support to mlx5 driver, from Jesper Dangaard Brouer. 5) Add ttl inherit support to vxlan, from Hangbin Liu. 6) Properly separate ipv6 routes into their logically independant components. fib6_info for the routing table, and fib6_nh for sets of nexthops, which thus can be shared. From David Ahern. 7) Add bpf_xdp_adjust_tail helper, which can be used to generate ICMP messages from XDP programs. From Nikita V. Shirokov. 8) Lots of long overdue cleanups to the r8169 driver, from Heiner Kallweit. 9) Add BTF ("BPF Type Format"), from Martin KaFai Lau. 10) Add traffic condition monitoring to iwlwifi, from Luca Coelho. 11) Plumb extack down into fib_rules, from Roopa Prabhu. 12) Add Flower classifier offload support to igb, from Vinicius Costa Gomes. 13) Add UDP GSO support, from Willem de Bruijn. 14) Add documentation for eBPF helpers, from Quentin Monnet. 15) Add TLS tx offload to mlx5, from Ilya Lesokhin. 16) Allow applications to be given the number of bytes available to read on a socket via a control message returned from recvmsg(), from Soheil Hassas Yeganeh. 17) Add x86_32 eBPF JIT compiler, from Wang YanQing. 18) Add AF_XDP sockets, with zerocopy support infrastructure as well. From Björn Töpel. 19) Remove indirect load support from all of the BPF JITs and handle these operations in the verifier by translating them into native BPF instead. From Daniel Borkmann. 20) Add GRO support to ipv6 gre tunnels, from Eran Ben Elisha. 21) Allow XDP programs to do lookups in the main kernel routing tables for forwarding. From David Ahern. 22) Allow drivers to store hardware state into an ELF section of kernel dump vmcore files, and use it in cxgb4. From Rahul Lakkireddy. 23) Various RACK and loss detection improvements in TCP, from Yuchung Cheng. 24) Add TCP SACK compression, from Eric Dumazet. 25) Add User Mode Helper support and basic bpfilter infrastructure, from Alexei Starovoitov. 26) Support ports and protocol values in RTM_GETROUTE, from Roopa Prabhu. 27) Support bulking in ->ndo_xdp_xmit() API, from Jesper Dangaard Brouer. 28) Add lots of forwarding selftests, from Petr Machata. 29) Add generic network device failover driver, from Sridhar Samudrala. * ra.kernel.org:/pub/scm/linux/kernel/git/davem/net-next: (1959 commits) strparser: Add __strp_unpause and use it in ktls. rxrpc: Fix terminal retransmission connection ID to include the channel net: hns3: Optimize PF CMDQ interrupt switching process net: hns3: Fix for VF mailbox receiving unknown message net: hns3: Fix for VF mailbox cannot receiving PF response bnx2x: use the right constant Revert "net: sched: cls: Fix offloading when ingress dev is vxlan" net: dsa: b53: Fix for brcm tag issue in Cygnus SoC enic: fix UDP rss bits netdev-FAQ: clarify DaveM's position for stable backports rtnetlink: validate attributes in do_setlink() mlxsw: Add extack messages for port_{un, }split failures netdevsim: Add extack error message for devlink reload devlink: Add extack to reload and port_{un, }split operations net: metrics: add proper netlink validation ipmr: fix error path when ipmr_new_table fails ip6mr: only set ip6mr_table from setsockopt when ip6mr_new_table succeeds net: hns3: remove unused hclgevf_cfg_func_mta_filter netfilter: provide udp*_lib_lookup for nf_tproxy qed*: Utilize FW 8.37.2.0 ...
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/bpf/README.rst36
-rw-r--r--Documentation/bpf/bpf_design_QA.rst221
-rw-r--r--Documentation/bpf/bpf_design_QA.txt156
-rw-r--r--Documentation/bpf/bpf_devel_QA.rst640
-rw-r--r--Documentation/bpf/bpf_devel_QA.txt570
-rw-r--r--Documentation/devicetree/bindings/arm/stm32/stm32-syscon.txt14
-rw-r--r--Documentation/devicetree/bindings/arm/stm32/stm32.txt (renamed from Documentation/devicetree/bindings/arm/stm32.txt)0
-rw-r--r--Documentation/devicetree/bindings/net/dsa/dsa.txt6
-rw-r--r--Documentation/devicetree/bindings/net/dsa/qca8k.txt23
-rw-r--r--Documentation/devicetree/bindings/net/dwmac-sun8i.txt21
-rw-r--r--Documentation/devicetree/bindings/net/fsl-tsec-phy.txt68
-rw-r--r--Documentation/devicetree/bindings/net/meson-dwmac.txt1
-rw-r--r--Documentation/devicetree/bindings/net/microchip,lan78xx.txt54
-rw-r--r--Documentation/devicetree/bindings/net/mscc-miim.txt26
-rw-r--r--Documentation/devicetree/bindings/net/mscc-ocelot.txt82
-rw-r--r--Documentation/devicetree/bindings/net/qualcomm-bluetooth.txt30
-rw-r--r--Documentation/devicetree/bindings/net/sff,sfp.txt4
-rw-r--r--Documentation/devicetree/bindings/net/sh_eth.txt1
-rw-r--r--Documentation/devicetree/bindings/net/socionext,uniphier-ave4.txt19
-rw-r--r--Documentation/devicetree/bindings/net/stm32-dwmac.txt18
-rw-r--r--Documentation/devicetree/bindings/net/wireless/qcom,ath10k.txt31
-rw-r--r--Documentation/devicetree/bindings/ptp/ptp-qoriq.txt69
-rw-r--r--Documentation/devicetree/bindings/soc/ti/keystone-navigator-qmss.txt9
-rw-r--r--Documentation/filesystems/nfs/nfsroot.txt70
-rw-r--r--Documentation/networking/6lowpan.txt4
-rw-r--r--Documentation/networking/af_xdp.rst312
-rw-r--r--Documentation/networking/bonding.txt2
-rw-r--r--Documentation/networking/e100.rst (renamed from Documentation/networking/e100.txt)60
-rw-r--r--Documentation/networking/e1000.rst (renamed from Documentation/networking/e1000.txt)59
-rw-r--r--Documentation/networking/failover.rst18
-rw-r--r--Documentation/networking/filter.txt21
-rw-r--r--Documentation/networking/gtp.txt4
-rw-r--r--Documentation/networking/ila.txt2
-rw-r--r--Documentation/networking/index.rst3
-rw-r--r--Documentation/networking/ip-sysctl.txt42
-rw-r--r--Documentation/networking/ipsec.txt4
-rw-r--r--Documentation/networking/ipvlan.txt4
-rw-r--r--Documentation/networking/kcm.txt10
-rw-r--r--Documentation/networking/net_failover.rst116
-rw-r--r--Documentation/networking/netdev-FAQ.txt9
-rw-r--r--Documentation/networking/netdev-features.txt7
-rw-r--r--Documentation/networking/nf_conntrack-sysctl.txt2
-rw-r--r--Documentation/sysctl/net.txt1
43 files changed, 1913 insertions, 936 deletions
diff --git a/Documentation/bpf/README.rst b/Documentation/bpf/README.rst
new file mode 100644
index 000000000000..b9a80c9e9392
--- /dev/null
+++ b/Documentation/bpf/README.rst
@@ -0,0 +1,36 @@
+=================
+BPF documentation
+=================
+
+This directory contains documentation for the BPF (Berkeley Packet
+Filter) facility, with a focus on the extended BPF version (eBPF).
+
+This kernel side documentation is still work in progress. The main
+textual documentation is (for historical reasons) described in
+`Documentation/networking/filter.txt`_, which describe both classical
+and extended BPF instruction-set.
+The Cilium project also maintains a `BPF and XDP Reference Guide`_
+that goes into great technical depth about the BPF Architecture.
+
+The primary info for the bpf syscall is available in the `man-pages`_
+for `bpf(2)`_.
+
+
+
+Frequently asked questions (FAQ)
+================================
+
+Two sets of Questions and Answers (Q&A) are maintained.
+
+* QA for common questions about BPF see: bpf_design_QA_
+
+* QA for developers interacting with BPF subsystem: bpf_devel_QA_
+
+
+.. Links:
+.. _bpf_design_QA: bpf_design_QA.rst
+.. _bpf_devel_QA: bpf_devel_QA.rst
+.. _Documentation/networking/filter.txt: ../networking/filter.txt
+.. _man-pages: https://www.kernel.org/doc/man-pages/
+.. _bpf(2): http://man7.org/linux/man-pages/man2/bpf.2.html
+.. _BPF and XDP Reference Guide: http://cilium.readthedocs.io/en/latest/bpf/
diff --git a/Documentation/bpf/bpf_design_QA.rst b/Documentation/bpf/bpf_design_QA.rst
new file mode 100644
index 000000000000..6780a6d81745
--- /dev/null
+++ b/Documentation/bpf/bpf_design_QA.rst
@@ -0,0 +1,221 @@
+==============
+BPF Design Q&A
+==============
+
+BPF extensibility and applicability to networking, tracing, security
+in the linux kernel and several user space implementations of BPF
+virtual machine led to a number of misunderstanding on what BPF actually is.
+This short QA is an attempt to address that and outline a direction
+of where BPF is heading long term.
+
+.. contents::
+ :local:
+ :depth: 3
+
+Questions and Answers
+=====================
+
+Q: Is BPF a generic instruction set similar to x64 and arm64?
+-------------------------------------------------------------
+A: NO.
+
+Q: Is BPF a generic virtual machine ?
+-------------------------------------
+A: NO.
+
+BPF is generic instruction set *with* C calling convention.
+-----------------------------------------------------------
+
+Q: Why C calling convention was chosen?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+A: Because BPF programs are designed to run in the linux kernel
+which is written in C, hence BPF defines instruction set compatible
+with two most used architectures x64 and arm64 (and takes into
+consideration important quirks of other architectures) and
+defines calling convention that is compatible with C calling
+convention of the linux kernel on those architectures.
+
+Q: can multiple return values be supported in the future?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+A: NO. BPF allows only register R0 to be used as return value.
+
+Q: can more than 5 function arguments be supported in the future?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+A: NO. BPF calling convention only allows registers R1-R5 to be used
+as arguments. BPF is not a standalone instruction set.
+(unlike x64 ISA that allows msft, cdecl and other conventions)
+
+Q: can BPF programs access instruction pointer or return address?
+-----------------------------------------------------------------
+A: NO.
+
+Q: can BPF programs access stack pointer ?
+------------------------------------------
+A: NO.
+
+Only frame pointer (register R10) is accessible.
+From compiler point of view it's necessary to have stack pointer.
+For example LLVM defines register R11 as stack pointer in its
+BPF backend, but it makes sure that generated code never uses it.
+
+Q: Does C-calling convention diminishes possible use cases?
+-----------------------------------------------------------
+A: YES.
+
+BPF design forces addition of major functionality in the form
+of kernel helper functions and kernel objects like BPF maps with
+seamless interoperability between them. It lets kernel call into
+BPF programs and programs call kernel helpers with zero overhead.
+As all of them were native C code. That is particularly the case
+for JITed BPF programs that are indistinguishable from
+native kernel C code.
+
+Q: Does it mean that 'innovative' extensions to BPF code are disallowed?
+------------------------------------------------------------------------
+A: Soft yes.
+
+At least for now until BPF core has support for
+bpf-to-bpf calls, indirect calls, loops, global variables,
+jump tables, read only sections and all other normal constructs
+that C code can produce.
+
+Q: Can loops be supported in a safe way?
+----------------------------------------
+A: It's not clear yet.
+
+BPF developers are trying to find a way to
+support bounded loops where the verifier can guarantee that
+the program terminates in less than 4096 instructions.
+
+Instruction level questions
+---------------------------
+
+Q: LD_ABS and LD_IND instructions vs C code
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Q: How come LD_ABS and LD_IND instruction are present in BPF whereas
+C code cannot express them and has to use builtin intrinsics?
+
+A: This is artifact of compatibility with classic BPF. Modern
+networking code in BPF performs better without them.
+See 'direct packet access'.
+
+Q: BPF instructions mapping not one-to-one to native CPU
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Q: It seems not all BPF instructions are one-to-one to native CPU.
+For example why BPF_JNE and other compare and jumps are not cpu-like?
+
+A: This was necessary to avoid introducing flags into ISA which are
+impossible to make generic and efficient across CPU architectures.
+
+Q: why BPF_DIV instruction doesn't map to x64 div?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+A: Because if we picked one-to-one relationship to x64 it would have made
+it more complicated to support on arm64 and other archs. Also it
+needs div-by-zero runtime check.
+
+Q: why there is no BPF_SDIV for signed divide operation?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+A: Because it would be rarely used. llvm errors in such case and
+prints a suggestion to use unsigned divide instead
+
+Q: Why BPF has implicit prologue and epilogue?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+A: Because architectures like sparc have register windows and in general
+there are enough subtle differences between architectures, so naive
+store return address into stack won't work. Another reason is BPF has
+to be safe from division by zero (and legacy exception path
+of LD_ABS insn). Those instructions need to invoke epilogue and
+return implicitly.
+
+Q: Why BPF_JLT and BPF_JLE instructions were not introduced in the beginning?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+A: Because classic BPF didn't have them and BPF authors felt that compiler
+workaround would be acceptable. Turned out that programs lose performance
+due to lack of these compare instructions and they were added.
+These two instructions is a perfect example what kind of new BPF
+instructions are acceptable and can be added in the future.
+These two already had equivalent instructions in native CPUs.
+New instructions that don't have one-to-one mapping to HW instructions
+will not be accepted.
+
+Q: BPF 32-bit subregister requirements
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Q: BPF 32-bit subregisters have a requirement to zero upper 32-bits of BPF
+registers which makes BPF inefficient virtual machine for 32-bit
+CPU architectures and 32-bit HW accelerators. Can true 32-bit registers
+be added to BPF in the future?
+
+A: NO. The first thing to improve performance on 32-bit archs is to teach
+LLVM to generate code that uses 32-bit subregisters. Then second step
+is to teach verifier to mark operations where zero-ing upper bits
+is unnecessary. Then JITs can take advantage of those markings and
+drastically reduce size of generated code and improve performance.
+
+Q: Does BPF have a stable ABI?
+------------------------------
+A: YES. BPF instructions, arguments to BPF programs, set of helper
+functions and their arguments, recognized return codes are all part
+of ABI. However when tracing programs are using bpf_probe_read() helper
+to walk kernel internal datastructures and compile with kernel
+internal headers these accesses can and will break with newer
+kernels. The union bpf_attr -> kern_version is checked at load time
+to prevent accidentally loading kprobe-based bpf programs written
+for a different kernel. Networking programs don't do kern_version check.
+
+Q: How much stack space a BPF program uses?
+-------------------------------------------
+A: Currently all program types are limited to 512 bytes of stack
+space, but the verifier computes the actual amount of stack used
+and both interpreter and most JITed code consume necessary amount.
+
+Q: Can BPF be offloaded to HW?
+------------------------------
+A: YES. BPF HW offload is supported by NFP driver.
+
+Q: Does classic BPF interpreter still exist?
+--------------------------------------------
+A: NO. Classic BPF programs are converted into extend BPF instructions.
+
+Q: Can BPF call arbitrary kernel functions?
+-------------------------------------------
+A: NO. BPF programs can only call a set of helper functions which
+is defined for every program type.
+
+Q: Can BPF overwrite arbitrary kernel memory?
+---------------------------------------------
+A: NO.
+
+Tracing bpf programs can *read* arbitrary memory with bpf_probe_read()
+and bpf_probe_read_str() helpers. Networking programs cannot read
+arbitrary memory, since they don't have access to these helpers.
+Programs can never read or write arbitrary memory directly.
+
+Q: Can BPF overwrite arbitrary user memory?
+-------------------------------------------
+A: Sort-of.
+
+Tracing BPF programs can overwrite the user memory
+of the current task with bpf_probe_write_user(). Every time such
+program is loaded the kernel will print warning message, so
+this helper is only useful for experiments and prototypes.
+Tracing BPF programs are root only.
+
+Q: bpf_trace_printk() helper warning
+------------------------------------
+Q: When bpf_trace_printk() helper is used the kernel prints nasty
+warning message. Why is that?
+
+A: This is done to nudge program authors into better interfaces when
+programs need to pass data to user space. Like bpf_perf_event_output()
+can be used to efficiently stream data via perf ring buffer.
+BPF maps can be used for asynchronous data sharing between kernel
+and user space. bpf_trace_printk() should only be used for debugging.
+
+Q: New functionality via kernel modules?
+----------------------------------------
+Q: Can BPF functionality such as new program or map types, new
+helpers, etc be added out of kernel module code?
+
+A: NO.
diff --git a/Documentation/bpf/bpf_design_QA.txt b/Documentation/bpf/bpf_design_QA.txt
deleted file mode 100644
index f3e458a0bb2f..000000000000
--- a/Documentation/bpf/bpf_design_QA.txt
+++ /dev/null
@@ -1,156 +0,0 @@
-BPF extensibility and applicability to networking, tracing, security
-in the linux kernel and several user space implementations of BPF
-virtual machine led to a number of misunderstanding on what BPF actually is.
-This short QA is an attempt to address that and outline a direction
-of where BPF is heading long term.
-
-Q: Is BPF a generic instruction set similar to x64 and arm64?
-A: NO.
-
-Q: Is BPF a generic virtual machine ?
-A: NO.
-
-BPF is generic instruction set _with_ C calling convention.
-
-Q: Why C calling convention was chosen?
-A: Because BPF programs are designed to run in the linux kernel
- which is written in C, hence BPF defines instruction set compatible
- with two most used architectures x64 and arm64 (and takes into
- consideration important quirks of other architectures) and
- defines calling convention that is compatible with C calling
- convention of the linux kernel on those architectures.
-
-Q: can multiple return values be supported in the future?
-A: NO. BPF allows only register R0 to be used as return value.
-
-Q: can more than 5 function arguments be supported in the future?
-A: NO. BPF calling convention only allows registers R1-R5 to be used
- as arguments. BPF is not a standalone instruction set.
- (unlike x64 ISA that allows msft, cdecl and other conventions)
-
-Q: can BPF programs access instruction pointer or return address?
-A: NO.
-
-Q: can BPF programs access stack pointer ?
-A: NO. Only frame pointer (register R10) is accessible.
- From compiler point of view it's necessary to have stack pointer.
- For example LLVM defines register R11 as stack pointer in its
- BPF backend, but it makes sure that generated code never uses it.
-
-Q: Does C-calling convention diminishes possible use cases?
-A: YES. BPF design forces addition of major functionality in the form
- of kernel helper functions and kernel objects like BPF maps with
- seamless interoperability between them. It lets kernel call into
- BPF programs and programs call kernel helpers with zero overhead.
- As all of them were native C code. That is particularly the case
- for JITed BPF programs that are indistinguishable from
- native kernel C code.
-
-Q: Does it mean that 'innovative' extensions to BPF code are disallowed?
-A: Soft yes. At least for now until BPF core has support for
- bpf-to-bpf calls, indirect calls, loops, global variables,
- jump tables, read only sections and all other normal constructs
- that C code can produce.
-
-Q: Can loops be supported in a safe way?
-A: It's not clear yet. BPF developers are trying to find a way to
- support bounded loops where the verifier can guarantee that
- the program terminates in less than 4096 instructions.
-
-Q: How come LD_ABS and LD_IND instruction are present in BPF whereas
- C code cannot express them and has to use builtin intrinsics?
-A: This is artifact of compatibility with classic BPF. Modern
- networking code in BPF performs better without them.
- See 'direct packet access'.
-
-Q: It seems not all BPF instructions are one-to-one to native CPU.
- For example why BPF_JNE and other compare and jumps are not cpu-like?
-A: This was necessary to avoid introducing flags into ISA which are
- impossible to make generic and efficient across CPU architectures.
-
-Q: why BPF_DIV instruction doesn't map to x64 div?
-A: Because if we picked one-to-one relationship to x64 it would have made
- it more complicated to support on arm64 and other archs. Also it
- needs div-by-zero runtime check.
-
-Q: why there is no BPF_SDIV for signed divide operation?
-A: Because it would be rarely used. llvm errors in such case and
- prints a suggestion to use unsigned divide instead
-
-Q: Why BPF has implicit prologue and epilogue?
-A: Because architectures like sparc have register windows and in general
- there are enough subtle differences between architectures, so naive
- store return address into stack won't work. Another reason is BPF has
- to be safe from division by zero (and legacy exception path
- of LD_ABS insn). Those instructions need to invoke epilogue and
- return implicitly.
-
-Q: Why BPF_JLT and BPF_JLE instructions were not introduced in the beginning?
-A: Because classic BPF didn't have them and BPF authors felt that compiler
- workaround would be acceptable. Turned out that programs lose performance
- due to lack of these compare instructions and they were added.
- These two instructions is a perfect example what kind of new BPF
- instructions are acceptable and can be added in the future.
- These two already had equivalent instructions in native CPUs.
- New instructions that don't have one-to-one mapping to HW instructions
- will not be accepted.
-
-Q: BPF 32-bit subregisters have a requirement to zero upper 32-bits of BPF
- registers which makes BPF inefficient virtual machine for 32-bit
- CPU architectures and 32-bit HW accelerators. Can true 32-bit registers
- be added to BPF in the future?
-A: NO. The first thing to improve performance on 32-bit archs is to teach
- LLVM to generate code that uses 32-bit subregisters. Then second step
- is to teach verifier to mark operations where zero-ing upper bits
- is unnecessary. Then JITs can take advantage of those markings and
- drastically reduce size of generated code and improve performance.
-
-Q: Does BPF have a stable ABI?
-A: YES. BPF instructions, arguments to BPF programs, set of helper
- functions and their arguments, recognized return codes are all part
- of ABI. However when tracing programs are using bpf_probe_read() helper
- to walk kernel internal datastructures and compile with kernel
- internal headers these accesses can and will break with newer
- kernels. The union bpf_attr -> kern_version is checked at load time
- to prevent accidentally loading kprobe-based bpf programs written
- for a different kernel. Networking programs don't do kern_version check.
-
-Q: How much stack space a BPF program uses?
-A: Currently all program types are limited to 512 bytes of stack
- space, but the verifier computes the actual amount of stack used
- and both interpreter and most JITed code consume necessary amount.
-
-Q: Can BPF be offloaded to HW?
-A: YES. BPF HW offload is supported by NFP driver.
-
-Q: Does classic BPF interpreter still exist?
-A: NO. Classic BPF programs are converted into extend BPF instructions.
-
-Q: Can BPF call arbitrary kernel functions?
-A: NO. BPF programs can only call a set of helper functions which
- is defined for every program type.
-
-Q: Can BPF overwrite arbitrary kernel memory?
-A: NO. Tracing bpf programs can _read_ arbitrary memory with bpf_probe_read()
- and bpf_probe_read_str() helpers. Networking programs cannot read
- arbitrary memory, since they don't have access to these helpers.
- Programs can never read or write arbitrary memory directly.
-
-Q: Can BPF overwrite arbitrary user memory?
-A: Sort-of. Tracing BPF programs can overwrite the user memory
- of the current task with bpf_probe_write_user(). Every time such
- program is loaded the kernel will print warning message, so
- this helper is only useful for experiments and prototypes.
- Tracing BPF programs are root only.
-
-Q: When bpf_trace_printk() helper is used the kernel prints nasty
- warning message. Why is that?
-A: This is done to nudge program authors into better interfaces when
- programs need to pass data to user space. Like bpf_perf_event_output()
- can be used to efficiently stream data via perf ring buffer.
- BPF maps can be used for asynchronous data sharing between kernel
- and user space. bpf_trace_printk() should only be used for debugging.
-
-Q: Can BPF functionality such as new program or map types, new
- helpers, etc be added out of kernel module code?
-A: NO.
diff --git a/Documentation/bpf/bpf_devel_QA.rst b/Documentation/bpf/bpf_devel_QA.rst
new file mode 100644
index 000000000000..0e7c1d946e83
--- /dev/null
+++ b/Documentation/bpf/bpf_devel_QA.rst
@@ -0,0 +1,640 @@
+=================================
+HOWTO interact with BPF subsystem
+=================================
+
+This document provides information for the BPF subsystem about various
+workflows related to reporting bugs, submitting patches, and queueing
+patches for stable kernels.
+
+For general information about submitting patches, please refer to
+`Documentation/process/`_. This document only describes additional specifics
+related to BPF.
+
+.. contents::
+ :local:
+ :depth: 2
+
+Reporting bugs
+==============
+
+Q: How do I report bugs for BPF kernel code?
+--------------------------------------------
+A: Since all BPF kernel development as well as bpftool and iproute2 BPF
+loader development happens through the netdev kernel mailing list,
+please report any found issues around BPF to the following mailing
+list:
+
+ netdev@vger.kernel.org
+
+This may also include issues related to XDP, BPF tracing, etc.
+
+Given netdev has a high volume of traffic, please also add the BPF
+maintainers to Cc (from kernel MAINTAINERS_ file):
+
+* Alexei Starovoitov <ast@kernel.org>
+* Daniel Borkmann <daniel@iogearbox.net>
+
+In case a buggy commit has already been identified, make sure to keep
+the actual commit authors in Cc as well for the report. They can
+typically be identified through the kernel's git tree.
+
+**Please do NOT report BPF issues to bugzilla.kernel.org since it
+is a guarantee that the reported issue will be overlooked.**
+
+Submitting patches
+==================
+
+Q: To which mailing list do I need to submit my BPF patches?
+------------------------------------------------------------
+A: Please submit your BPF patches to the netdev kernel mailing list:
+
+ netdev@vger.kernel.org
+
+Historically, BPF came out of networking and has always been maintained
+by the kernel networking community. Although these days BPF touches
+many other subsystems as well, the patches are still routed mainly
+through the networking community.
+
+In case your patch has changes in various different subsystems (e.g.
+tracing, security, etc), make sure to Cc the related kernel mailing
+lists and maintainers from there as well, so they are able to review
+the changes and provide their Acked-by's to the patches.
+
+Q: Where can I find patches currently under discussion for BPF subsystem?
+-------------------------------------------------------------------------
+A: All patches that are Cc'ed to netdev are queued for review under netdev
+patchwork project:
+
+ http://patchwork.ozlabs.org/project/netdev/list/
+
+Those patches which target BPF, are assigned to a 'bpf' delegate for
+further processing from BPF maintainers. The current queue with
+patches under review can be found at:
+
+ https://patchwork.ozlabs.org/project/netdev/list/?delegate=77147
+
+Once the patches have been reviewed by the BPF community as a whole
+and approved by the BPF maintainers, their status in patchwork will be
+changed to 'Accepted' and the submitter will be notified by mail. This
+means that the patches look good from a BPF perspective and have been
+applied to one of the two BPF kernel trees.
+
+In case feedback from the community requires a respin of the patches,
+their status in patchwork will be set to 'Changes Requested', and purged
+from the current revie