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

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Message-ID: <c6a38a1b6f27ae787dbfd99df225f464c274590e.camel@surriel.com>
Date: Thu, 27 Feb 2025 20:13:49 -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 12:12 -0600, Tom Lendacky wrote:
> 
> As long as you keep the ASID value in EDX[15:0] as 0, then you won't
> #GP. ASID 0 is the host/hypervisor. An ASID > 0 belongs to a guest.
> 
I've been spending some time reading the KVM code,
and I don't think invlpgb would be currently useful
with KVM.

>From reading pre_svm_run(), new_asid(), and svm_vcpu_run(),
it looks like the ASID number used might be different for
each VCPU, assigned on a per (physical host) CPU basis.

It would take some surgery to change that around.

Some googling around also suggests that the ASID address
space is even more limited than the PCID address space :(

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