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: <1f5d53596e2ac8948332570e3bda17c3877fd499.camel@xry111.site>
Date: Thu, 11 Apr 2024 22:48:07 +0800
From: Xi Ruoyao <xry111@...111.site>
To: Dave Hansen <dave.hansen@...el.com>, 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 Thu, 2024-04-11 at 07:44 -0700, Dave Hansen wrote:
> On 4/11/24 03:48, Xi Ruoyao wrote:
> > +	/*
> > +	 * The Intel errata claims: "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 we are safe if we are surely running in a hypervisor.
> > +	 */
> 
> When you revise this, could you please work to make this more succinct?
> The Intel language on these things tends to be a bit flowery and is not
> always well-suited for the kernel.

Oops, bad timing.  I just sent v7 before getting this reply.

I'm not a native English speaker, so could you give some hint about how
to write this comment clearly?

> Also, saying that the erratum "claims" this casts doubt on it.  That's
> counterproductive.  I believe the current documentation is correct.  My
> original ce0b15d11ad8 ("x86/mm: Avoid incomplete Global INVLPG flushes")
> should have considered virtualized systems immune to this issue.

Then do we need a "Fixes: ce0b15d11ad8" for the patch keeping PCID
enabled for guests?

> I agree that it sounds weird.  It _is_ weird that systems running under
> hypervisors aren't affected.  But that's all it is: a weird bug.  The
> documentation is correct.

Yes, these hardware issues are just weird to me...

-- 
Xi Ruoyao <xry111@...111.site>
School of Aerospace Science and Technology, Xidian University