Re: [PATCH v8 0/8] KVM: x86: nSVM: Improve PAT virtualization

[Sean Christopherson]

On Tue, 07 Apr 2026 12:03:23 -0700, Jim Mattson wrote:
> 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 AMD 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 independent PATs for L1 and L2 when nested NPT
> is enabled, but only when a new quirk, KVM_X86_QUIRK_NESTED_SVM_SHARED_PAT,
> is disabled. By default, the quirk is enabled, preserving KVM's legacy
> behavior. When the quirk is disabled, KVM correctly virtualizes a separate
> PAT register for L2, using the g_pat field in the VMCB.
> 
> [...]

Applied to kvm-x86 svm.  Yosry and/or Jim, please double check the result, the
goof with patch 5 was slightly more annoying than I was expecting.

Thanks!

[1/8] KVM: x86: Define KVM_X86_QUIRK_NESTED_SVM_SHARED_PAT
      https://github.com/kvm-x86/linux/commit/822790ab0149
[2/8] KVM: x86: nSVM: Clear VMCB_NPT clean bit when updating hPAT from guest mode
      https://github.com/kvm-x86/linux/commit/0a8aeb15848e
[3/8] KVM: x86: nSVM: Cache and validate vmcb12 g_pat
      https://github.com/kvm-x86/linux/commit/4b83e4ba836e
[4/8] KVM: x86: nSVM: Set vmcb02.g_pat correctly for nested NPT
      https://github.com/kvm-x86/linux/commit/02233c73f8ae
[6/8] KVM: x86: nSVM: Save gPAT to vmcb12.g_pat on VMEXIT
      https://github.com/kvm-x86/linux/commit/d65cf222b899
[7/8] KVM: Documentation: document KVM_{GET,SET}_NESTED_STATE for SVM
      https://github.com/kvm-x86/linux/commit/32ebdbce3b23
[8/8] KVM: x86: nSVM: Save/restore gPAT with KVM_{GET,SET}_NESTED_STATE
      https://github.com/kvm-x86/linux/commit/4f256d5770fe

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https://github.com/kvm-x86/linux/tree/next