linux-kernel - Re: [PATCH v6] x86/mm: Don't disable INVLPG if "incomplete Global INVLPG flushes" is fixed by microcode or the kernel is running in a hypervisor

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Message-ID: <Zhfzvv6_ZENQ1_7Z@google.com>
Date: Thu, 11 Apr 2024 07:29:18 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Xi Ruoyao <xry111@...111.site>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>, Michael Kelley <mhklinux@...look.com>, 
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, Andy Lutomirski <luto@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>, 
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org, 
	linux-kernel@...r.kernel.org, Andrew Cooper <andrew.cooper3@...rix.com>
Subject: Re: [PATCH v6] x86/mm: Don't disable INVLPG if "incomplete Global
 INVLPG flushes" is fixed by microcode or the kernel is running in a hypervisor

On Thu, Apr 11, 2024, Xi Ruoyao wrote:
> Per the "Processor Specification Update" documentations referred by the
> intel-microcode-20240312 release note, this microcode release has fixed
> the issue for all affected models.
> 
> So don't disable INVLPG if the microcode is new enough.  The precise
> minimum microcode revision fixing the issue is provided by engineer from
> Intel.
> 
> And the erratum says:
> 
>     This erratum does not apply in VMX non-root operation. It applies
>     only when PCIDs are enabled and either in VMX root operation or
>     outside VMX operation.
> 
> So if the kernel is running in a hypervisor, we are in VMX non-root
> operation and we should be safe.

This should be two separate patches, one to do the precise ucode update check,
and one to keep PCID enabled for guests.