From 1b7fcd3263e5f12dba43d27b64e1578bec070c28 Mon Sep 17 00:00:00 2001 From: Avi Kivity Date: Thu, 15 May 2008 13:51:35 +0300 Subject: KVM: MMU: Fix false flooding when a pte points to page table The KVM MMU tries to detect when a speculative pte update is not actually used by demand fault, by checking the accessed bit of the shadow pte. If the shadow pte has not been accessed, we deem that page table flooded and remove the shadow page table, allowing further pte updates to proceed without emulation. However, if the pte itself points at a page table and only used for write operations, the accessed bit will never be set since all access will happen through the emulator. This is exactly what happens with kscand on old (2.4.x) HIGHMEM kernels. The kernel points a kmap_atomic() pte at a page table, and then proceeds with read-modify-write operations to look at the dirty and accessed bits. We get a false flood trigger on the kmap ptes, which results in the mmu spending all its time setting up and tearing down shadows. Fix by setting the shadow accessed bit on emulated accesses. Signed-off-by: Avi Kivity --- include/asm-x86/kvm_host.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include') diff --git a/include/asm-x86/kvm_host.h b/include/asm-x86/kvm_host.h index 844f2a89afb..c2d066e185f 100644 --- a/include/asm-x86/kvm_host.h +++ b/include/asm-x86/kvm_host.h @@ -243,6 +243,7 @@ struct kvm_vcpu_arch { gfn_t last_pt_write_gfn; int last_pt_write_count; u64 *last_pte_updated; + gfn_t last_pte_gfn; struct { gfn_t gfn; /* presumed gfn during guest pte update */ -- cgit v1.2.3