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| author | Sean Christopherson <seanjc@google.com> | 2021-10-09 05:11:56 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-03-08 21:12:34 +0300 |
| commit | 32b758d12c24d7fc385e359d6a54ebbb29960485 (patch) | |
| tree | 245dcbbaf38a373d41336b2b8597852428cd7e8e | |
| parent | b63190d0203faf25491f83d28273facc7a333ecf (diff) | |
| download | linux-32b758d12c24d7fc385e359d6a54ebbb29960485.tar.xz | |
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>
| -rw-r--r-- | arch/s390/kvm/kvm-s390.c | 2 | ||||
| -rw-r--r-- | virt/kvm/kvm_main.c | 5 |
2 files changed, 4 insertions, 3 deletions
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index 9a8c086528f5..402597f9d050 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -3447,7 +3447,7 @@ bool kvm_arch_no_poll(struct kvm_vcpu *vcpu) { /* do not poll with more than halt_poll_max_steal percent of steal time */ if (S390_lowcore.avg_steal_timer * 100 / (TICK_USEC << 12) >= - halt_poll_max_steal) { + READ_ONCE(halt_poll_max_steal)) { vcpu->stat.halt_no_poll_steal++; return true; } diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 13aff136e6ee..f8b42e19bc77 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -3222,6 +3222,7 @@ 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; @@ -3229,7 +3230,7 @@ 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; @@ -3284,7 +3285,7 @@ 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) { |