linux-kernel - Re: [PATCH v9 03/12] x86/mm: consolidate full flush threshold decision

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Message-ID: <1edea8a714fd1df0734f7fe15bb690e4c3a556dc.camel@surriel.com>
Date: Fri, 07 Feb 2025 15:22:59 -0500
From: Rik van Riel <riel@...riel.com>
To: Brendan Jackman <jackmanb@...gle.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, bp@...en8.de, 
	peterz@...radead.org, dave.hansen@...ux.intel.com,
 zhengqi.arch@...edance.com, 	nadav.amit@...il.com, thomas.lendacky@....com,
 kernel-team@...a.com, 	linux-mm@...ck.org, akpm@...ux-foundation.org,
 jannh@...gle.com, 	mhklinux@...look.com, andrew.cooper3@...rix.com, Dave
 Hansen	 <dave.hansen@...el.com>
Subject: Re: [PATCH v9 03/12] x86/mm: consolidate full flush threshold
 decision

On Fri, 2025-02-07 at 15:50 +0100, Brendan Jackman wrote:
> On Thu, 6 Feb 2025 at 05:45, Rik van Riel <riel@...riel.com> wrote:
> > @@ -1276,7 +1282,7 @@ void arch_tlbbatch_flush(struct
> > arch_tlbflush_unmap_batch *batch)
> > 
> >         int cpu = get_cpu();
> > 
> > -       info = get_flush_tlb_info(NULL, 0, TLB_FLUSH_ALL, 0, false,
> > +       info = get_flush_tlb_info(NULL, 0, TLB_FLUSH_ALL,
> > PAGE_SHIFT, false,
> >                                   TLB_GENERATION_INVALID);
> 
> [Why] do we need this change? If it's necessary here, why isn't it
> needed everywhere else that does TLB_FLUSH_ALL too, like
> flush_tlb_mm()?
> 
flush_tlb_mm() calls flush_tlb_mm_range(), which
does also use get_flush_tlb_info().

We pass in PAGE_SHIFT here to ensure that the
stride shift is specified correctly to the
INVLPGB instruction later on.


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