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| author | Sean Christopherson <seanjc@google.com> | 2021-10-08 19:11:56 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-01-27 12:02:38 +0100 |
| commit | 69bbdf32f04178cef945945439181296dd51d23a (patch) | |
| tree | de6be3212646ba375304b082d044f233fe46d0e3 /virt | |
| parent | aa59606d5b93cf0c4c4b86a40fffd32f4453c6ed (diff) | |
| download | linux-69bbdf32f04178cef945945439181296dd51d23a.tar.gz linux-69bbdf32f04178cef945945439181296dd51d23a.tar.bz2 linux-69bbdf32f04178cef945945439181296dd51d23a.zip | |
KVM: s390: Ensure kvm_arch_no_poll() is read once when blocking vCPU
[ Upstream commit 6f390916c4fb359507d9ac4bf1b28a4f8abee5c0 ]
Wrap s390's halt_poll_max_steal with READ_ONCE and snapshot the result of
kvm_arch_no_poll() in kvm_vcpu_block() to avoid a mostly-theoretical,
largely benign bug on s390 where the result of kvm_arch_no_poll() could
change due to userspace modifying halt_poll_max_steal while the vCPU is
blocking. The bug is largely benign as it will either cause KVM to skip
updating halt-polling times (no_poll toggles false=>true) or to update
halt-polling times with a slightly flawed block_ns.
Note, READ_ONCE is unnecessary in the current code, add it in case the
arch hook is ever inlined, and to provide a hint that userspace can
change the param at will.
Fixes: 8b905d28ee17 ("KVM: s390: provide kvm_arch_no_poll function")
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211009021236.4122790-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'virt')
| -rw-r--r-- | virt/kvm/kvm_main.c | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 72c4e6b39389..5bd62342c482 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -3153,6 +3153,7 @@ update_halt_poll_stats(struct kvm_vcpu *vcpu, u64 poll_ns, bool waited) */ void kvm_vcpu_block(struct kvm_vcpu *vcpu) { + bool halt_poll_allowed = !kvm_arch_no_poll(vcpu); ktime_t start, cur, poll_end; bool waited = false; u64 block_ns; @@ -3160,7 +3161,7 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) kvm_arch_vcpu_blocking(vcpu); start = cur = poll_end = ktime_get(); - if (vcpu->halt_poll_ns && !kvm_arch_no_poll(vcpu)) { + if (vcpu->halt_poll_ns && halt_poll_allowed) { ktime_t stop = ktime_add_ns(ktime_get(), vcpu->halt_poll_ns); ++vcpu->stat.generic.halt_attempted_poll; @@ -3215,7 +3216,7 @@ out: update_halt_poll_stats( vcpu, ktime_to_ns(ktime_sub(poll_end, start)), waited); - if (!kvm_arch_no_poll(vcpu)) { + if (halt_poll_allowed) { if (!vcpu_valid_wakeup(vcpu)) { shrink_halt_poll_ns(vcpu); } else if (vcpu->kvm->max_halt_poll_ns) { |