Stable commit 23249dade2 ("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 fbc7e61195 ("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 9b19700e62 ("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: <stable@vger.kernel.org> # 5.15.y
Fixes: 23249dade2 ("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>
20fc1431bc