From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
Michael Kelley <mhklinux@outlook.com>,
Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Xi Ruoyao <xry111@xry111.site>
Subject: Re: [RFC PATCH] KVM: x86: Advertise PCID based on hardware support (with an asterisk)
Date: Thu, 11 Apr 2024 12:11:46 -0700 [thread overview]
Message-ID: <Zhg18kSHFeWN1xJH@google.com> (raw)
In-Reply-To: <bd8e7f8b-532f-4372-a3fd-69893e359b42@redhat.com>
On Thu, Apr 11, 2024, Paolo Bonzini wrote:
> On 4/11/24 18:31, Sean Christopherson wrote:
> > Force set a synthetic feature, GUEST_PCID, if PCID can be safely used in
> > virtual machines, even if the kernel itself disables PCID support, and
> > advertise PCID support in KVM if GUEST_PCID is set.
> >
> > When running on a CPU that is affected by Intel's "Global INVLPG" erratum,
> > which does NOT affect VMX non-root mode, it is safe to virtualize PCID for
> > KVM guests, even though it is not safe for the kernel itself to enable PCID.
> > Ditto for if the kernel disables PCID because CR4.PGE isn't supported.
>
> But the guest would not use it if the f/m/s matches, right?
Maybe? There's another in-flight patch for dealing with the guest side of
things.
https://lore.kernel.org/all/20240411144322.14585-2-xry111@xry111.site
> If the advantage is basically not splitting the migration pool, is that a
> concern for the affected Alder Lake/Gracemont/Raptor Lake processors?
I have put _zero_ thought into what value this actually adds (another reason I
tagged it RFC). This was purely a "it's easy, so why not".
prev parent reply other threads:[~2024-04-11 19:11 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-11 16:31 [RFC PATCH] KVM: x86: Advertise PCID based on hardware support (with an asterisk) Sean Christopherson
2024-04-11 16:36 ` Paolo Bonzini
2024-04-11 19:11 ` Sean Christopherson [this message]
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