[v2,0/8] KVM: Fix mmu_notifier vs. pfncache vs. pfncache races

Message

Sean Christopherson April 27, 2022, 1:39 a.m. UTC

Fix races between mmu_notifier invalidation and pfncache refresh, and
within the pfncache itself.

The first two patches are reverts of the patches sitting in kvm/queue,
trying to separate and fix the races independently is nigh impossible.
I assume/hope they can be ignored and the original patches dropped.

I verified internal races using the attached hack-a-test.  Running the
test against the current implementation fails due to KVM writing the
current GPA into the wrong page.

I don't think the race with the mmu_notifier is technically proven, e.g. I
never encountered a use-after-free even running with KASAN.

Ran with PROVE_LOCKING and DEBUG_ATOMIC_SLEEP, so in theory there shouldn't
be any lurking locking goofs this time...

v2:
  - Map the pfn=>khva outside of gpc->lock. [Maxim]
  - Fix a page leak.
  - Fix more races.

v1:
  https://lore.kernel.org/all/[e-mail]

Sean Christopherson (8):
  Revert "KVM: Do not speculatively mark pfn cache valid to "fix" race"
  Revert "KVM: Fix race between mmu_notifier invalidation and pfncache
    refresh"
  KVM: Drop unused @gpa param from gfn=>pfn cache's __release_gpc()
    helper
  KVM: Put the extra pfn reference when reusing a pfn in the gpc cache
  KVM: Do not incorporate page offset into gfn=>pfn cache user address
  KVM: Fix multiple races in gfn=>pfn cache refresh
  KVM: Do not pin pages tracked by gfn=>pfn caches
  DO NOT MERGE: Hack-a-test to verify gpc invalidation+refresh

 arch/x86/kvm/x86.c                     |  30 ++++
 include/linux/kvm_host.h               |   2 +
 include/linux/kvm_types.h              |   1 +
 tools/testing/selftests/kvm/.gitignore |   1 +
 tools/testing/selftests/kvm/Makefile   |   2 +
 tools/testing/selftests/kvm/gpc_test.c | 217 +++++++++++++++++++++++++
 virt/kvm/pfncache.c                    | 188 +++++++++++++--------
 7 files changed, 372 insertions(+), 69 deletions(-)
 create mode 100644 tools/testing/selftests/kvm/gpc_test.c


base-commit: 2a39d8b39bffdaf1a4223d0d22f07baee154c8f3