linux-kernel - Re: [PATCH 09/12] x86/mm: enable broadcast TLB invalidation for multi-threaded processes

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Message-ID: <20250101161556.lniuomixy75vmj5g@ed.ac.uk>
Date: Wed, 1 Jan 2025 16:15:56 +0000
From: Karim Manaouil <kmanaouil.dev@...il.com>
To: Nadav Amit <nadav.amit@...il.com>
Cc: Rik van Riel <riel@...riel.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	kernel-team@...a.com, Dave Hansen <dave.hansen@...ux.intel.com>,
	luto@...nel.org, peterz@...radead.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	zhengqi.arch@...edance.com,
	"open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>
Subject: Re: [PATCH 09/12] x86/mm: enable broadcast TLB invalidation for
 multi-threaded processes

On Wed, Jan 01, 2025 at 05:20:01PM +0200, Nadav Amit wrote:
> 
> 
> On 01/01/2025 6:42, Rik van Riel wrote:
> > Fixed for the next version.
> 
> Thanks Rik,
> 
> Admittedly, I don't feel great about my overall last review - it mostly
> focused on style and common BKMs.
> 
> I still don't quite get the entire logic. To name one thing that I don't
> understand: why do we need broadcast_asid_list and the complicated games of
> syncing it with broadcast_asid_used. Why wouldn't broadcast_asid_used
> suffice?

If I uderstand correctly from Rik's patch, I think the list is needed to
save the flush for only when we run out of the ASID space (wrap around).
Without the list, whenever the ASID bit is cleared, you also have to flush
the TLBs.

> 
> 
> 

-- 
Best,
Karim
Edinburgh University