linux-kernel - Re: [RFC PATCH v3 0/7] Intel RAR TLB invalidation

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Message-ID: <46d299f1-f358-4920-9528-4b3381cd065c@intel.com>
Date: Thu, 5 Jun 2025 09:58:14 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Sean Christopherson <seanjc@...gle.com>, Rik van Riel <riel@...riel.com>
Cc: linux-kernel@...r.kernel.org, kernel-team@...a.com,
 dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
 bp@...en8.de, x86@...nel.org, nadav.amit@...il.com, tglx@...utronix.de
Subject: Re: [RFC PATCH v3 0/7] Intel RAR TLB invalidation

On 6/5/25 09:50, Sean Christopherson wrote:
>> This patch series is based off a 2019 patch series created by Intel
> Do you have performance numbers?  IIRC, the reason that 2019 series never went
> anywhere is because RAR wasn't a win for bare metal.  Though I believe it _was_
> a win for KVM, due to the cost of an IPI being significantly higher (requires a
> VM-Exit => VM-Enter roundtrip).

I'd love to see some performance numbers too.

But the real problem with the 2019 series was that it didn't have a
global PCID space at all, only the per-cpu space. That greatly limited
how RAR could be used.

I suspect now that Rik added the global space for INVLPGB that we'll
have better luck with RAR.