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: <cca972cc-8135-4037-9e4b-ac34dc600965@intel.com>
Date: Thu, 11 Apr 2024 08:43:29 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Xi Ruoyao <xry111@...111.site>, Dave Hansen
 <dave.hansen@...ux.intel.com>, Michael Kelley <mhklinux@...look.com>,
 Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc: 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,
 Sean Christopherson <seanjc@...gle.com>,
 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 4/11/24 08:18, Dave Hansen wrote:
> 
>> I'm not a native English speaker, so could you give some hint about how
>> to write this comment clearly?
> Something like this would be fine:
> 
> 	/* Only bare-metal is affected.  PCIDs in guests are OK. */

One more thing...  Instead if cluttering up the main PCID setup path
that everybody has to read, you can put this in the macro:

#define INTEL_MATCH(_model)		    \
	{				    \
	  .vendor  = X86_VENDOR_INTEL,      \
	  .feature = X86_FEATURE_HYPERVISOR \
          .family  = 6,                     \
	  .model   = _model,                \
	}

Then you can supplement the "INVLPG may not properly flush Global
entries..." comment.

/*
  * INVLPG may not properly flush Global entries. But
  * it only misbehaves when PCIDs are in use on bare
  * metal on specific CPU models. It is completely
  * fixed with updated microcode.
  */