Fix accessed bit tracking

The kvm mmu synchronizes shadow ptes using the mmu lock, however the cpu will happily ignore the lock when setting the accessed bit. This can cause the accessed bit to be lost. Luckily this only results in incorrect page selection for swap.

This patchset fixes the problem by atomically updating the spte when needed while taking care of the accessed bit.

v3: fix i386 pte exchange code in patch 3
add missing __set_spte() to drop_spte() in patch 2

v2: fix incorrect code transformations in first patch

Avi Kivity (4):
KVM: MMU: Introduce drop_spte()
KVM: MMU: Move accessed/dirty bit checks from rmap_remove() to

    drop_spte()

KVM: MMU: Atomically check for accessed bit when dropping an spte
KVM: MMU: Don't drop accessed bit while updating an spte

 arch/x86/kvm/mmu.c         |   88 +++++++++++++++++++++++++++++++------------
 arch/x86/kvm/paging_tmpl.h |   13 +++---
 2 files changed, 69 insertions(+), 32 deletions(-)