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

From: Sean Christopherson
Date: Tue Apr 26 2022 - 21:40:17 EST

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...

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


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
KVM: Drop unused @gpa param from gfn=>pfn cache's __release_gpc()
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