linux-kernel - Re: [PATCH v4 4/7] mm/x86: Make pud

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Message-ID: <87bk240y8h.ffs@tglx>
Date: Thu, 08 Aug 2024 00:22:38 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Peter Xu <peterx@...hat.com>, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org
Cc: "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>, Michael Ellerman
 <mpe@...erman.id.au>, Oscar Salvador <osalvador@...e.de>, Dan Williams
 <dan.j.williams@...el.com>, James Houghton <jthoughton@...gle.com>,
 Matthew Wilcox <willy@...radead.org>, Nicholas Piggin <npiggin@...il.com>,
 Rik van Riel <riel@...riel.com>, Dave Jiang <dave.jiang@...el.com>, Andrew
 Morton <akpm@...ux-foundation.org>, x86@...nel.org, Ingo Molnar
 <mingo@...hat.com>, Rick P Edgecombe <rick.p.edgecombe@...el.com>, "Kirill
 A . Shutemov" <kirill@...temov.name>, peterx@...hat.com,
 linuxppc-dev@...ts.ozlabs.org, Mel Gorman <mgorman@...hsingularity.net>,
 Hugh Dickins <hughd@...gle.com>, Borislav Petkov <bp@...en8.de>, David
 Hildenbrand <david@...hat.com>, Vlastimil Babka <vbabka@...e.cz>, Dave
 Hansen <dave.hansen@...ux.intel.com>, Christophe Leroy
 <christophe.leroy@...roup.eu>, Huang Ying <ying.huang@...el.com>
Subject: Re: [PATCH v4 4/7] mm/x86: Make pud_leaf() only care about PSE bit

On Wed, Aug 07 2024 at 15:48, Peter Xu wrote:
> An entry should be reported as PUD leaf even if it's PROT_NONE, in which
> case PRESENT bit isn't there. I hit bad pud without this when testing dax
> 1G on zapping a PROT_NONE PUD.

That does not qualify as a change log. What you hit is irrelevant unless
you explain the actual underlying problem. See Documentation/process/
including the TIP documentation.

> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
> index e39311a89bf4..a2a3bd4c1bda 100644
> --- a/arch/x86/include/asm/pgtable.h
> +++ b/arch/x86/include/asm/pgtable.h
> @@ -1078,8 +1078,7 @@ static inline pmd_t *pud_pgtable(pud_t pud)
>  #define pud_leaf pud_leaf
>  static inline bool pud_leaf(pud_t pud)
>  {
> -	return (pud_val(pud) & (_PAGE_PSE | _PAGE_PRESENT)) ==
> -		(_PAGE_PSE | _PAGE_PRESENT);
> +	return pud_val(pud) & _PAGE_PSE;
>  }

And the changelog does not explain why this change is not affecting any
existing user of pud_leaf().

Thanks,

        tglx