From: Paul Mackerras <pau...@ozlabs.org>
[ 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 <pau...@ozlabs.org>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
arch/powerpc/kvm/book3s_64_mmu_radix.c | 5 +++++
1 file changed, 5 insertions(+)
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);
}
--
2.25.1
