linux-kernel - Re: [PATCH v13 06/14] x86/mm: use broadcast TLB flushing for page reclaim TLB flushing

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Message-ID: <9086371cfe69760780d67ec279f69e91f65086a7.camel@surriel.com>
Date: Wed, 26 Feb 2025 12:46:13 -0500
From: Rik van Riel <riel@...riel.com>
To: Tom Lendacky <thomas.lendacky@....com>, Borislav Petkov <bp@...en8.de>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, peterz@...radead.org, 
	dave.hansen@...ux.intel.com, zhengqi.arch@...edance.com,
 nadav.amit@...il.com, 	kernel-team@...a.com, linux-mm@...ck.org,
 akpm@...ux-foundation.org, 	jackmanb@...gle.com, jannh@...gle.com,
 mhklinux@...look.com, 	andrew.cooper3@...rix.com, Manali.Shukla@....com,
 mingo@...nel.org
Subject: Re: [PATCH v13 06/14] x86/mm: use broadcast TLB flushing for page
 reclaim TLB flushing

On Wed, 2025-02-26 at 11:36 -0600, Tom Lendacky wrote:
> 
> Right, but the ASID valid bit is not set, so the flushing may match
> more
> than just host/hypervisor TLB entries.
> 
Good point, when using SVM these flushes could result
in flushing more TLB entries than we really want.

On the flip side, when SVM is not initialized, the
invlpgb instruction will fail with a general protection
fault if we have anything at all in the ASID field.

I don't know whether setting the ASID valid bit in
rAX will cause a system to crash when SVM is not
enabled or initialized.

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