linux-kernel - Re: [PATCH v5 00/12] AMD broadcast TLB invalidation

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Message-ID: <da35b3a2-6b48-4cf9-a6f8-39e28a3b022f@citrix.com>
Date: Fri, 17 Jan 2025 00:00:33 +0000
From: Andrew Cooper <andrew.cooper3@...rix.com>
To: Peter Zijlstra <peterz@...radead.org>,
 Michael Kelley <mhklinux@...look.com>
Cc: "riel@...riel.com" <riel@...riel.com>, "x86@...nel.org" <x86@...nel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "bp@...en8.de" <bp@...en8.de>,
 "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
 "zhengqi.arch@...edance.com" <zhengqi.arch@...edance.com>,
 "nadav.amit@...il.com" <nadav.amit@...il.com>,
 "thomas.lendacky@....com" <thomas.lendacky@....com>,
 "kernel-team@...a.com" <kernel-team@...a.com>,
 "linux-mm@...ck.org" <linux-mm@...ck.org>,
 "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
 "jannh@...gle.com" <jannh@...gle.com>
Subject: Re: [PATCH v5 00/12] AMD broadcast TLB invalidation

On 16/01/2025 10:37 pm, Peter Zijlstra wrote:
> On Thu, Jan 16, 2025 at 06:14:00PM +0000, Michael Kelley wrote:
>> So CoCo
>> VMs may still use the paravirtualization that makes hypercalls to do
>> TLB flushes. It's future work to *always* use INVLPGB (if available)
>> in a CoCo VM.
> That would place a limit on the number of CPUs, to be no larger than the
> number of available ASIDs.

Can you please be specific between PCID (the x86 architectural thing
commonly called ASID) or ASID (the thing named by the AMD architecture).

INVLPGB instruction under virt can use PCIDs to its hearts content, but
ASIDs are rewritten behind the scenes because VM does not usually know
the ASID the VMM assigned to it.

~Andrew