This is a note to let you know that I've just added the patch titled KVM: PPC: Book3S HV: Close race with page faults around memslot flushes to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: kvm-ppc-book3s-hv-close-race-with-page-faults-around.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit dc986d581356691417a7d69ea9ca8343ccfbca58 Author: Paul Mackerras <paulus@xxxxxxxxxx> Date: Thu May 28 10:56:42 2020 +1000 KVM: PPC: Book3S HV: Close race with page faults around memslot flushes [ Upstream commit 11362b1befeadaae4d159a8cddcdaf6b8afe08f9 ] There is a potential race condition between hypervisor page faults and flushing a memslot. It is possible for a page fault to read the memslot before a memslot is updated and then write a PTE to the partition-scoped page tables after kvmppc_radix_flush_memslot has completed. (Note that this race has never been explicitly observed.) To close this race, it is sufficient to increment the MMU sequence number while the kvm->mmu_lock is held. That will cause mmu_notifier_retry() to return true, and the page fault will then return to the guest without inserting a PTE. Signed-off-by: Paul Mackerras <paulus@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/arch/powerpc/kvm/book3s_64_mmu_radix.c b/arch/powerpc/kvm/book3s_64_mmu_radix.c index da8375437d161..9d73448354698 100644 --- a/arch/powerpc/kvm/book3s_64_mmu_radix.c +++ b/arch/powerpc/kvm/book3s_64_mmu_radix.c @@ -1104,6 +1104,11 @@ void kvmppc_radix_flush_memslot(struct kvm *kvm, kvm->arch.lpid); gpa += PAGE_SIZE; } + /* + * Increase the mmu notifier sequence number to prevent any page + * fault that read the memslot earlier from writing a PTE. + */ + kvm->mmu_notifier_seq++; spin_unlock(&kvm->mmu_lock); }