linux-kernel - Re: [PATCH v5 03/12] x86/mm: consolidate full flush threshold decision

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Message-ID: <bc7b621deaa75bd6d641fef272e5b045916515e5.camel@surriel.com>
Date: Fri, 17 Jan 2025 14:32:29 -0500
From: Rik van Riel <riel@...riel.com>
To: Michael Kelley <mhklinux@...look.com>, "x86@...nel.org" <x86@...nel.org>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
 "bp@...en8.de"	 <bp@...en8.de>, "peterz@...radead.org"
 <peterz@...radead.org>,  "dave.hansen@...ux.intel.com"	
 <dave.hansen@...ux.intel.com>, "zhengqi.arch@...edance.com"	
 <zhengqi.arch@...edance.com>, "nadav.amit@...il.com"
 <nadav.amit@...il.com>,  "thomas.lendacky@....com"	
 <thomas.lendacky@....com>, "kernel-team@...a.com" <kernel-team@...a.com>, 
 "linux-mm@...ck.org"	 <linux-mm@...ck.org>, "akpm@...ux-foundation.org"
 <akpm@...ux-foundation.org>,  "jannh@...gle.com"	 <jannh@...gle.com>,
 "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>,  Dave Hansen
 <dave.hansen@...el.com>
Subject: Re: [PATCH v5 03/12] x86/mm: consolidate full flush threshold
 decision

On Fri, 2025-01-17 at 19:23 +0000, Michael Kelley wrote:
> From: riel@...riel.com <riel@...riel.com> Sent: Wednesday, January
> 15, 2025 6:30 PM
> > 
> > -		info = get_flush_tlb_info(NULL, start, end, 0,
> > false,
> > -					  TLB_GENERATION_INVALID);
> > +	guard(preempt)();
> > +
> > +	info = get_flush_tlb_info(NULL, start, end, PAGE_SHIFT,
> > false,
> > +				  TLB_GENERATION_INVALID);
> > 
> > +	if (end == TLB_FLUSH_ALL)
> 
> This needs to test "info->end", not "end".
> 
> In my VM on Hyper-V *without* INVLPGB support, the bug causes
> boot to hang as it tries to individually flush each page in the
> [0, TLB_FLUSH_ALL] range. :-)

Ohhhh, good catch.

I guess on bare metal the automatic tests that run
on every kernel build didn't notice the slower
boot, because it's not as severe of an impact as
in a virtual machine.

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