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| author | Will Deacon <will@kernel.org> | 2025-10-03 19:40:54 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2025-10-12 12:56:20 +0200 |
| commit | 250b6e009ff97f69411aa109116ac720d54f45ec (patch) | |
| tree | 2ce4a63ff9231e312f8ed6bf4c8e9f54eefcadd1 | |
| parent | e617101e562654c7d59ed5cfcd30f610f1f64411 (diff) | |
| download | linux-250b6e009ff97f69411aa109116ac720d54f45ec.tar.gz linux-250b6e009ff97f69411aa109116ac720d54f45ec.tar.bz2 linux-250b6e009ff97f69411aa109116ac720d54f45ec.zip | |
KVM: arm64: Fix softirq masking in FPSIMD register saving sequence
Stable commit 28b82be094e2 ("KVM: arm64: Fix kernel BUG() due to bad
backport of FPSIMD/SVE/SME fix") fixed a kernel BUG() caused by a bad
backport of upstream commit fbc7e61195e2 ("KVM: arm64: Unconditionally
save+flush host FPSIMD/SVE/SME state") by ensuring that softirqs are
disabled/enabled across the fpsimd register save operation.
Unfortunately, although this fixes the original issue, it can now lead
to deadlock when re-enabling softirqs causes pending softirqs to be
handled with locks already held:
| BUG: spinlock recursion on CPU#7, CPU 3/KVM/57616
| lock: 0xffff3045ef850240, .magic: dead4ead, .owner: CPU 3/KVM/57616, .owner_cpu: 7
| CPU: 7 PID: 57616 Comm: CPU 3/KVM Tainted: G O 6.1.152 #1
| Hardware name: SoftIron SoftIron Platform Mainboard/SoftIron Platform Mainboard, BIOS 1.31 May 11 2023
| Call trace:
| dump_backtrace+0xe4/0x110
| show_stack+0x20/0x30
| dump_stack_lvl+0x6c/0x88
| dump_stack+0x18/0x34
| spin_dump+0x98/0xac
| do_raw_spin_lock+0x70/0x128
| _raw_spin_lock+0x18/0x28
| raw_spin_rq_lock_nested+0x18/0x28
| update_blocked_averages+0x70/0x550
| run_rebalance_domains+0x50/0x70
| handle_softirqs+0x198/0x328
| __do_softirq+0x1c/0x28
| ____do_softirq+0x18/0x28
| call_on_irq_stack+0x30/0x48
| do_softirq_own_stack+0x24/0x30
| do_softirq+0x74/0x90
| __local_bh_enable_ip+0x64/0x80
| fpsimd_save_and_flush_cpu_state+0x5c/0x68
| kvm_arch_vcpu_put_fp+0x4c/0x88
| kvm_arch_vcpu_put+0x28/0x88
| kvm_sched_out+0x38/0x58
| __schedule+0x55c/0x6c8
| schedule+0x60/0xa8
Take a tiny step towards the upstream fix in 9b19700e623f ("arm64:
fpsimd: Drop unneeded 'busy' flag") by additionally disabling hardirqs
while saving the fpsimd registers.
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Lee Jones <lee@kernel.org>
Cc: Sasha Levin <sashal@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: <stable@vger.kernel.org> # 6.6.y
Fixes: 28b82be094e2 ("KVM: arm64: Fix kernel BUG() due to bad backport of FPSIMD/SVE/SME fix")
Reported-by: Kenneth Van Alstyne <kvanals@kvanals.org>
Link: https://lore.kernel.org/r/010001999bae0958-4d80d25d-8dda-4006-a6b9-798f3e774f6c-000000@email.amazonses.com
Signed-off-by: Will Deacon <will@kernel.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | arch/arm64/kernel/fpsimd.c | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c index d0d836448a76..83827384982e 100644 --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -1873,13 +1873,17 @@ static void fpsimd_flush_cpu_state(void) */ void fpsimd_save_and_flush_cpu_state(void) { + unsigned long flags; + if (!system_supports_fpsimd()) return; WARN_ON(preemptible()); - get_cpu_fpsimd_context(); + local_irq_save(flags); + __get_cpu_fpsimd_context(); fpsimd_save(); fpsimd_flush_cpu_state(); - put_cpu_fpsimd_context(); + __put_cpu_fpsimd_context(); + local_irq_restore(flags); } #ifdef CONFIG_KERNEL_MODE_NEON |