[PATCH 0/4] KVM: x86/mmu: MMIO caching bug fixes

Sean Christopherson
2022-07-28T22:18:12Z

Fix two bugs I introduced when adding the enable_mmio_caching module param.

Bug #1 is that KVM unintentionally makes disabling caching due to a config
incompatibility "sticky", e.g. disabling caching because there are no
reserved PA bits prevents KVM from enabling when "switching" to an EPT
config (doesn't rely on PA bits) or when SVM adjusts the MMIO masks to
account for C-bit shenanigans (even if MAXPHYADDR=52 and C-bit=51, there
can be reserved PA bits due to the "real" MAXPHYADDR being reduced).

Bug #2 is that KVM doesn't explicitly check that MMIO caching is enabled
when doing SEV-ES setup. Prior to the module param, MMIO caching was
guaranteed when SEV-ES could be enabled as SEV-ES-capable CPUs effectively
guarantee there will be at least one reserved PA bit (see above). With
the module param, userspace can explicitly disable MMIO caching, thus
silently breaking SEV-ES.

I believe I tested all combinations of things getting disabled and enabled
by hacking kvm_mmu_reset_all_pte_masks() to disable MMIO caching on a much
lower MAXPHYADDR, e.g. 43 instead of 52. That said, definitely wait for a
thumbs up from the AMD folks before queueing.

Sean Christopherson (4):
KVM: x86: Tag kvm_mmu_x86_module_init() with __init
KVM: x86/mmu: Fully re-evaluate MMIO caching when SPTE masks change
KVM: SVM: Adjust MMIO masks (for caching) before doing SEV(-ES) setup
KVM: SVM: Disable SEV-ES support if MMIO caching is disable

arch/x86/include/asm/kvm_host.h | 2 +-
arch/x86/kvm/mmu.h | 2 ++
arch/x86/kvm/mmu/mmu.c | 6 +++++-
arch/x86/kvm/mmu/spte.c | 20 ++++++++++++++++++++
arch/x86/kvm/mmu/spte.h | 3 +--
arch/x86/kvm/svm/sev.c | 10 ++++++++++
arch/x86/kvm/svm/svm.c | 9 ++++++---
7 files changed, 45 insertions(+), 7 deletions(-)

base-commit: 1a4d88a361af4f2e91861d632c6a1fe87a9665c2
--
2.37.1.455.g008518b4e5-goog