Currently, KVM's implementation of nested SVM treats the PAT MSR the same
way whether or not nested NPT is enabled: L1 and L2 share a single
PAT. However, the APM specifies that when nested NPT is enabled, the host
(L1) and the guest (L2) should have independent PATs: hPAT for L1 and gPAT
for L2. This patch series implements the architectural specification in
KVM.
The existing PAT MSR (vcpu->arch.pat) is used for hPAT, and the
vmcb02.save.g_pat field is used for gPAT. With nested NPT enabled, guest
accesses to the IA32_PAT MSR are redirected to gPAT, which is stored in
vmcb02->save.g_pat. All other accesses, including userspace accesses via
KVM_{GET,SET}_MSRS, continue to reference hPAT.
The special handling of userspace accesses ensures save/restore forward
compatibility (i.e. resuming a new checkpoint on an older kernel). When an
old kernel restores a checkpoint from a new kernel, the gPAT will be lost,
and L2 will simply use L1's PAT, which is the behavior of the old kernel
anyway.
v1 -> v2:
Adhere to the architectural specification
Drop the preservation of vmcb01->g_pat across virtual SMM
Store the gPAT rather than the hPAT in the nested state (save.g_pat)
Fix forward compatibility
Handle backward compatibility when MSRs are restored after nested state
(setq-default fill-column 75) [Sean]
Or the KVM_STATE_SVM_VALID_GPAT bit into flags [Sean]
Jim Mattson (8):
KVM: x86: nSVM: Redirect IA32_PAT accesses to either hPAT or gPAT
KVM: x86: nSVM: Cache g_pat in vmcb_save_area_cached
KVM: x86: nSVM: Add validity check for vmcb12 g_pat
KVM: x86: nSVM: Set vmcb02.g_pat correctly for nested NPT
KVM: x86: nSVM: Save gPAT to vmcb12.g_pat on VMEXIT
KVM: x86: nSVM: Save/restore gPAT with KVM_{GET,SET}_NESTED_STATE
KVM: x86: nSVM: Handle restore of legacy nested state
KVM: selftests: nSVM: Add svm_nested_pat test
arch/x86/include/uapi/asm/kvm.h | 3 +
arch/x86/kvm/svm/nested.c | 49 ++-
arch/x86/kvm/svm/svm.c | 39 +-
arch/x86/kvm/svm/svm.h | 7 +
tools/testing/selftests/kvm/Makefile.kvm | 1 +
.../selftests/kvm/x86/svm_nested_pat_test.c | 357 ++++++++++++++++++
6 files changed, 442 insertions(+), 14 deletions(-)
create mode 100644 tools/testing/selftests/kvm/x86/svm_nested_pat_test.c
base-commit: f62b64b970570c92fe22503b0cdc65be7ce7fc7c
--
2.52.0.457.g6b5491de43-goog
