linux-kernel - Re: [PATCH v4 05/12] x86/mm: add INVLPGB support code

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Message-ID: <7045d1666ac5722820a43fffa7f2e6fb3c2eb485.camel@surriel.com>
Date: Mon, 13 Jan 2025 16:10:41 -0500
From: Rik van Riel <riel@...riel.com>
To: Tom Lendacky <thomas.lendacky@....com>, x86@...nel.org
Cc: linux-kernel@...r.kernel.org, bp@...en8.de, peterz@...radead.org, 
	dave.hansen@...ux.intel.com, zhengqi.arch@...edance.com,
 nadav.amit@...il.com, 	kernel-team@...a.com, linux-mm@...ck.org,
 akpm@...ux-foundation.org, 	jannh@...gle.com
Subject: Re: [PATCH v4 05/12] x86/mm: add INVLPGB support code

On Mon, 2025-01-13 at 08:21 -0600, Tom Lendacky wrote:
> On 1/12/25 09:53, Rik van Riel wrote:
> > 
> > +static inline void __invlpgb(unsigned long asid, unsigned long
> > pcid, unsigned long addr,
> > +			    int extra_count, bool pmd_stride,
> > unsigned long flags)
> > +{
> > +	u32 edx = (pcid << 16) | asid;
> > +	u32 ecx = (pmd_stride << 31);
> > +	u64 rax = addr | flags;
> > +
> > +	/* Protect against negative numbers. */
> > +	extra_count = max(extra_count, 0);
> > +	ecx |= extra_count;
> 
> A bad ECX value (ECX[15:0] > invlpgb_count_max) will result in a #GP,
> is
> that ok?

The calling code ensures we do not call this code
with more than invlpgb_count_max pages at a time.

Given the choice between "a bug in the calling code
crashes the kernel" and "a bug in the calling code
results in a missed TLB flush", I'm guessing the
crash is probably better.

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