linux-kernel - Re: [PATCH v5 10/12] x86,tlb: do targeted broadcast flushing from tlbbatch code

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Message-ID: <11fcbbbb545576a1bfa54839cf87a72faf5603ab.camel@surriel.com>
Date: Mon, 20 Jan 2025 12:56:45 -0500
From: Rik van Riel <riel@...riel.com>
To: Nadav Amit <nadav.amit@...il.com>
Cc: the arch/x86 maintainers <x86@...nel.org>, Linux Kernel Mailing List
	 <linux-kernel@...r.kernel.org>, Borislav Petkov <bp@...en8.de>, 
	peterz@...radead.org, Dave Hansen <dave.hansen@...ux.intel.com>, 
	zhengqi.arch@...edance.com, thomas.lendacky@....com, kernel-team@...a.com, 
 "open list:MEMORY MANAGEMENT"
	 <linux-mm@...ck.org>, Andrew Morton <akpm@...ux-foundation.org>, 
	jannh@...gle.com, mhklinux@...look.com, andrew.cooper3@...rix.com
Subject: Re: [PATCH v5 10/12] x86,tlb: do targeted broadcast flushing from
 tlbbatch code

On Mon, 2025-01-20 at 19:50 +0200, Nadav Amit wrote:
> [ Thanks for your patience. ]
> 
> > On 20 Jan 2025, at 19:11, Rik van Riel <riel@...riel.com> wrote:
> > 
> > On Mon, 2025-01-20 at 19:09 +0200, Nadav Amit wrote:
> > 
> > This is the page reclaim code.
> > 
> > The process that has those other pages mapped might be
> > running on other CPUs simultaneously with the page
> > reclaim code.
> > 
> > Even if we were invalidating one of our own pages this
> > way, there could be other threads in the same process,
> > running while we are in the page reclaim code.
> 
> 
> 
> Of course, but there is nothing new here. Let me see where we lose
> each other by first stating the goal, what you propose, and what I
> suggest.
> 
> We are issuing invlpgb and we need to ensure tlbsync on the same core
> that initiated invlpgb before arch_tlbbatch_flush() finishes. That’s
> all that matters for our discussion (correct me if I miss something).
> 
> You solved it by disabling migration and running tlbsync at the end.
> 
> I suggest *not* to disable migration, to keep running tlbsync at the
> arch_tlbbatch_flush() as you do, and if context-switch happens after
> arch_tlbbatch_add_pending() and before arch_tlbbatch_flush(), to run
> tlbsync during the context switch.
> 
How would you keep track of CPUs where the tlbsync
has NOT happened before arch_tlbbatch_flush()?

That part seems to be missing still.

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