Re: [PATCH v13 02/35] KVM: Assert that mmu_invalidate_in_progress *never* goes negative
From: Fuad Tabba <hidden>
Date: 2023-11-01 12:47:04
Also in:
kvm, kvm-riscv, kvmarm, linux-fsdevel, linux-mips, linux-mm, linux-riscv, linuxppc-dev, lkml
On Fri, Oct 27, 2023 at 7:22 PM Sean Christopherson [off-list ref] wrote:
Move the assertion on the in-progress invalidation count from the primary MMU's notifier path to KVM's common notification path, i.e. assert that the count doesn't go negative even when the invalidation is coming from KVM itself. Opportunistically convert the assertion to a KVM_BUG_ON(), i.e. kill only the affected VM, not the entire kernel. A corrupted count is fatal to the VM, e.g. the non-zero (negative) count will cause mmu_invalidate_retry() to block any and all attempts to install new mappings. But it's far from guaranteed that an end() without a start() is fatal or even problematic to anything other than the target VM, e.g. the underlying bug could simply be a duplicate call to end(). And it's much more likely that a missed invalidation, i.e. a potential use-after-free, would manifest as no notification whatsoever, not an end() without a start(). Signed-off-by: Sean Christopherson <seanjc@google.com> ---
Reviewed-by: Fuad Tabba <redacted> Tested-by: Fuad Tabba <redacted> Cheers, /fuad
quoted hunk ↗ jump to hunk
virt/kvm/kvm_main.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 0524933856d4..5a97e6c7d9c2 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c@@ -833,6 +833,7 @@ void kvm_mmu_invalidate_end(struct kvm *kvm, unsigned long start, * in conjunction with the smp_rmb in mmu_invalidate_retry(). */ kvm->mmu_invalidate_in_progress--; + KVM_BUG_ON(kvm->mmu_invalidate_in_progress < 0, kvm); } static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,@@ -863,8 +864,6 @@ static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn, */ if (wake) rcuwait_wake_up(&kvm->mn_memslots_update_rcuwait); - - BUG_ON(kvm->mmu_invalidate_in_progress < 0); } static int kvm_mmu_notifier_clear_flush_young(struct mmu_notifier *mn, --2.42.0.820.g83a721a137-goog
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