linux-kernel - Re: [PATCh 0/3] x86,tlb: context switch optimizations

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20241114144007.GB39245@noisy.programming.kicks-ass.net>
Date: Thu, 14 Nov 2024 15:40:07 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Rik van Riel <riel@...riel.com>
Cc: Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
	linux-kernel@...r.kernel.org, dave.hansen@...ux.intel.com,
	luto@...nel.org, tglx@...utronix.de, mingo@...hat.com,
	x86@...nel.org, kernel-team@...a.com, hpa@...or.com,
	bigeasy@...utronix.de
Subject: Re: [PATCh 0/3] x86,tlb: context switch optimizations

On Thu, Nov 14, 2024 at 09:27:25AM -0500, Rik van Riel wrote:

> 1) Move the interrupt re-enabling up (probably not this one?)

Correct, that one is wrong for it results in IPIs that we don't want or
need.

> 2) Explicitly clear the mm_cpumask bit in unuse_temporary_mm()
> 
> 3) Have unuse_temporary_mm increment the mm's tlb_gen, since that
>    is the only thing flush_tlb_mm_range really does for an MM
>    without any bits set in the mm_cpumask.

So flush_tlb_mm_range() has an 'mm == loaded_mm' case, which does a
local flush. I *think* we're not hitting that because switch_mm() does a
write to loaded_mm() just before this.

But I don't think we want to proliferate the logic contained in
flush_tlb_mm_range() further than we have to.

So my preference goes to 2, as that seems to be the safest option.
Notably text_poke() it not concerned with performance much.