From: Sean Christopherson <seanjc@google.com>
To: Jim Mattson <jmattson@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Thomas Gleixner <tglx@kernel.org>, Ingo Molnar <mingo@redhat.com>,
Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Shuah Khan <shuah@kernel.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-kselftest@vger.kernel.org,
Yosry Ahmed <yosry.ahmed@linux.dev>
Subject: Re: [PATCH v3 7/8] KVM: x86: nSVM: Handle restore of legacy nested state
Date: Fri, 6 Feb 2026 11:17:59 -0800 [thread overview]
Message-ID: <aYY-ZwjEnHbY5J-T@google.com> (raw)
In-Reply-To: <20260205214326.1029278-8-jmattson@google.com>
On Thu, Feb 05, 2026, Jim Mattson wrote:
> When nested NPT is enabled and KVM_SET_NESTED_STATE is used to restore an
> old checkpoint (without a valid gPAT), the current IA32_PAT value must be
> used as L2's gPAT.
>
> The current IA32_PAT value may be restored by KVM_SET_MSRS after
> KVM_SET_NESTED_STATE. Furthermore, there may be a KVM_GET_NESTED_STATE
> before the first KVM_RUN.
>
> Introduce a new boolean, svm->nested.legacy_gpat_semantics. When set, hPAT
> updates are also applied to gPAT, preserving the old behavior where L2
> shared L1's PAT. svm_vcpu_pre_run() clears this boolean at the first
> KVM_RUN.
State this last point as a command and explain why. E.g. I think this is why?
Clear legacy_gpat_semantics on KVM_RUN so that the legacy semantics are
scoped to a single restore (inasmuch as possible). E.g. to support
restoring a snapshot from an old KVM, and then later restoring a snapshot
from a new KVM.
next prev parent reply other threads:[~2026-02-06 19:18 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-05 21:43 [PATCH v3 0/8] KVM: x86: nSVM: Improve PAT virtualization Jim Mattson
2026-02-05 21:43 ` [PATCH v3 1/8] KVM: x86: nSVM: Clear VMCB_NPT clean bit when updating g_pat in L2 Jim Mattson
2026-02-09 16:05 ` Yosry Ahmed
2026-02-05 21:43 ` [PATCH v3 2/8] KVM: x86: nSVM: Cache and validate vmcb12 g_pat Jim Mattson
2026-02-06 18:19 ` Sean Christopherson
2026-02-06 18:23 ` Yosry Ahmed
2026-02-06 18:32 ` Jim Mattson
2026-02-06 19:12 ` Sean Christopherson
2026-02-06 19:15 ` Yosry Ahmed
2026-02-06 19:50 ` Sean Christopherson
2026-02-06 20:56 ` Jim Mattson
2026-02-06 23:07 ` Sean Christopherson
2026-02-05 21:43 ` [PATCH v3 3/8] KVM: x86: nSVM: Set vmcb02.g_pat correctly for nested NPT Jim Mattson
2026-02-06 18:23 ` Sean Christopherson
2026-02-06 18:29 ` Yosry Ahmed
2026-02-06 19:14 ` Sean Christopherson
2026-02-05 21:43 ` [PATCH v3 4/8] KVM: x86: nSVM: Redirect IA32_PAT accesses to either hPAT or gPAT Jim Mattson
2026-02-05 21:43 ` [PATCH v3 5/8] KVM: x86: nSVM: Save gPAT to vmcb12.g_pat on VMEXIT Jim Mattson
2026-02-05 21:43 ` [PATCH v3 6/8] KVM: x86: nSVM: Save/restore gPAT with KVM_{GET,SET}_NESTED_STATE Jim Mattson
2026-02-05 21:43 ` [PATCH v3 7/8] KVM: x86: nSVM: Handle restore of legacy nested state Jim Mattson
2026-02-06 19:17 ` Sean Christopherson [this message]
2026-02-06 22:38 ` Jim Mattson
2026-02-05 21:43 ` [PATCH v3 8/8] KVM: selftests: nSVM: Add svm_nested_pat test Jim Mattson
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