From: Sean Christopherson <seanjc@google.com>
To: Christian Ludloff <ludloff@gmail.com>
Cc: Jim Mattson <jmattson@google.com>,
David Kaplan <David.Kaplan@amd.com>,
"pbonzini@redhat.com" <pbonzini@redhat.com>,
"tglx@kernel.org" <tglx@kernel.org>,
"mingo@redhat.com" <mingo@redhat.com>,
"bp@alien8.de" <bp@alien8.de>,
"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
"x86@kernel.org" <x86@kernel.org>,
"hpa@zytor.com" <hpa@zytor.com>,
"shuah@kernel.org" <shuah@kernel.org>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
linux-kselftest@vger.kernel.org,
"ctpence@google.com" <ctpence@google.com>
Subject: Re: [PATCH v3 3/4] KVM: x86: Virtualize AMD CPUID faulting
Date: Thu, 28 May 2026 17:00:12 -0700 [thread overview]
Message-ID: <ahjXDGrBcOGDq8kZ@google.com> (raw)
In-Reply-To: <CAKSQd8VrNC5F_7c8SCsuJHe1oFMJBCZc97Ez3ZAUfabUay8ZzA@mail.gmail.com>
On Thu, May 28, 2026, Christian Ludloff wrote:
> > It appears it was a deliberate decision, due in part to the fact that the
> > traditional flow of checking CPL exceptions before intercepts typically
> > applies to using instructions in an illegal way, but the user is not doing
> > anything illegal here by executing CPUID which is normally a legal
> > instruction at CPL3.
> >
> > That said, clearly the behavior is different now between the vendors,
> > however at this point the feedback I got is that our architects want to
> > stick with the existing behavior unless there is a strong reason that it is
> > a problem for SW.
>
> What is a HV expected to do for such a CPUID guest exit?
Emulate hardware behavior. The only question we had was whether the observed
hardware behavior (VM-Exit takes precedence over #GP) was AMD's architectural
behavior.
next prev parent reply other threads:[~2026-05-29 0:00 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-28 22:01 [PATCH v3 3/4] KVM: x86: Virtualize AMD CPUID faulting Christian Ludloff
2026-05-29 0:00 ` Sean Christopherson [this message]
-- strict thread matches above, loose matches on Subject: below --
2026-05-13 22:46 [PATCH v3 0/4] KVM: x86: Virtualize AMD's "disable CPUID in usermode" Jim Mattson
2026-05-13 22:46 ` [PATCH v3 3/4] KVM: x86: Virtualize AMD CPUID faulting Jim Mattson
2026-05-14 13:19 ` Jim Mattson
2026-05-14 14:28 ` Sean Christopherson
2026-05-14 14:45 ` Jim Mattson
2026-05-14 16:20 ` Sean Christopherson
2026-05-14 16:22 ` Jim Mattson
2026-05-14 16:35 ` Sean Christopherson
2026-05-14 18:01 ` Jim Mattson
2026-05-14 18:17 ` Kaplan, David
2026-05-26 18:38 ` Jim Mattson
[not found] ` <DS7PR12MB82011943131DF5415365E19E940B2@DS7PR12MB8201.namprd12.prod.outlook.com>
2026-05-27 13:25 ` Jim Mattson
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