From: Sean Christopherson <seanjc@google.com>
To: Jim Mattson <jmattson@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Jonathan Corbet <corbet@lwn.net>,
Shuah Khan <skhan@linuxfoundation.org>,
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>,
kvm@vger.kernel.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, Yosry Ahmed <yosry@kernel.org>
Subject: Re: [PATCH] KVM: x86: nSVM: Redirect IA32_PAT accesses to either hPAT or gPAT
Date: Tue, 7 Apr 2026 12:24:31 -0700 [thread overview]
Message-ID: <adVZ7-EiekghvDMD@google.com> (raw)
In-Reply-To: <20260407190343.325299-6-jmattson@google.com>
On Tue, Apr 07, 2026, Jim Mattson wrote:
> When KVM_X86_QUIRK_NESTED_SVM_SHARED_PAT is disabled and the vCPU is in
> guest mode with nested NPT enabled, guest accesses to IA32_PAT are
> redirected to the gPAT register, which is stored in VMCB02's g_pat field.
>
> Non-guest accesses (e.g. from userspace) to IA32_PAT are always redirected
> to hPAT, which is stored in vcpu->arch.pat.
>
> Directing host-initiated accesses to hPAT ensures that KVM_GET/SET_MSRS and
> KVM_GET/SET_NESTED_STATE are independent of each other and can be ordered
> arbitrarily during save and restore. gPAT is saved and restored separately
> via KVM_GET/SET_NESTED_STATE.
>
> Use WARN_ON_ONCE to flag any host-initiated accesses originating from KVM
> itself rather than userspace.
>
> Use pr_warn_once to flag any use of the common MSR-handling code (now
> shared by VMX and TDX) for IA32_PAT by a vCPU that is SVM-capable.
Changelog is stale, but otherwise this LGTM. I'll fixup the changelog when
applying (in a few weeks).
next prev parent reply other threads:[~2026-04-07 19:24 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-07 19:03 [PATCH v8 0/8] KVM: x86: nSVM: Improve PAT virtualization Jim Mattson
2026-04-07 19:03 ` [PATCH v8 1/8] KVM: x86: Define KVM_X86_QUIRK_NESTED_SVM_SHARED_PAT Jim Mattson
2026-04-07 19:03 ` [PATCH v8 2/8] KVM: x86: nSVM: Clear VMCB_NPT clean bit when updating hPAT from guest mode Jim Mattson
2026-04-07 19:03 ` [PATCH v8 3/8] KVM: x86: nSVM: Cache and validate vmcb12 g_pat Jim Mattson
2026-04-07 19:03 ` [PATCH v8 4/8] KVM: x86: nSVM: Set vmcb02.g_pat correctly for nested NPT Jim Mattson
2026-04-07 19:03 ` [PATCH] KVM: x86: nSVM: Redirect IA32_PAT accesses to either hPAT or gPAT Jim Mattson
2026-04-07 19:24 ` Sean Christopherson [this message]
2026-04-07 20:51 ` Jim Mattson
2026-04-07 19:03 ` [PATCH v8 6/8] KVM: x86: nSVM: Save gPAT to vmcb12.g_pat on VMEXIT Jim Mattson
2026-04-07 19:03 ` [PATCH v8 7/8] KVM: Documentation: document KVM_{GET,SET}_NESTED_STATE for SVM Jim Mattson
2026-04-07 19:03 ` [PATCH v8 8/8] KVM: x86: nSVM: Save/restore gPAT with KVM_{GET,SET}_NESTED_STATE Jim Mattson
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