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: <7590c66d-96dd-4182-b99b-9a618a2a8f1c@citrix.com>
Date: Thu, 11 Apr 2024 16:00:06 +0100
From: Andrew Cooper <andrew.cooper3@...rix.com>
To: Xi Ruoyao <xry111@...111.site>, 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>
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 11/04/2024 3:48 pm, Xi Ruoyao wrote:
> On Thu, 2024-04-11 at 07:44 -0700, Dave Hansen wrote:
>> 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...
>

I have no inside knowledge here, but this isn't surprising to me.

VPID tags are unique to VMX operation.  At a guess, VMXON reconfigures
the tagging in the TLB to include VPID (and EPTP tags for that matter),
and works around the buggy selection for which PCIDs to drop.

~Andrew