From: Yosry Ahmed <yosry@kernel.org>
To: Sean Christopherson <seanjc@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, Jim Mattson <jmattson@google.com>
Subject: Re: [PATCH v8 0/8] KVM: x86: nSVM: Improve PAT virtualization
Date: Thu, 21 May 2026 02:36:21 +0000 [thread overview]
Message-ID: <ag5vj3q2r7NdYFQY@google.com> (raw)
In-Reply-To: <ag4ZwD53B7a0ivgT@google.com>
On Wed, May 20, 2026 at 08:30:31PM +0000, Yosry Ahmed wrote:
> On Mon, May 18, 2026 at 05:41:06PM -0700, Sean Christopherson wrote:
> > 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.
>
> The result looks good to me. I also ran the selftest from v7 and it
> passes. I couldn't help myself from reworking it and cleaning it up, I
> will send a patch your way soon.
As promised, if you want something you can directly run against the
current kvm-x86 svm:
https://lore.kernel.org/kvm/20260521023448.3826878-1-yosry@kernel.org/
prev parent reply other threads:[~2026-05-21 2:36 UTC|newest]
Thread overview: 15+ 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
2026-04-07 20:51 ` Jim Mattson
2026-04-07 23:52 ` Sean Christopherson
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
2026-05-19 0:41 ` [PATCH v8 0/8] KVM: x86: nSVM: Improve PAT virtualization Sean Christopherson
2026-05-20 20:30 ` Yosry Ahmed
2026-05-21 2:36 ` Yosry Ahmed [this message]
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