linux-kernel - Re: [PATCH] mm: move mask update out of the atomic context

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Message-ID: <75717e4e-51d0-41a2-8463-45097fc3875b@redhat.com>
Date: Tue, 24 Jun 2025 11:40:05 +0200
From: David Hildenbrand <david@...hat.com>
To: Alexander Gordeev <agordeev@...ux.ibm.com>
Cc: Dev Jain <dev.jain@....com>, Andrew Morton <akpm@...ux-foundation.org>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: move mask update out of the atomic context

On 24.06.25 11:37, Alexander Gordeev wrote:
> On Mon, Jun 23, 2025 at 09:45:34PM +0200, David Hildenbrand wrote:
> ...
>> Let's ask the real questions: who checks PGTBL_PTE_MODIFIED?
>>
>> I see
>>
>> if (mask & ARCH_PAGE_TABLE_SYNC_MASK)
>> 	arch_sync_kernel_mappings(start, start + size);
>>
>> And then
>>
>> arch/arm/include/asm/page.h:#define ARCH_PAGE_TABLE_SYNC_MASK   PGTBL_PMD_MODIFIED
>> arch/x86/include/asm/pgtable-2level_types.h:#define ARCH_PAGE_TABLE_SYNC_MASK   PGTBL_PMD_MODIFIED
>> arch/x86/include/asm/pgtable-3level_types.h:#define ARCH_PAGE_TABLE_SYNC_MASK   PGTBL_PMD_MODIFIED
>>
>>
>> Which makes me wonder why we need PGTBL_PTE_MODIFIED at all? Is there some other check I am missing?
>>
>> (same question regarding everything excepy PGTBL_PMD_MODIFIED, because that actually seems to be used)
> 
> AFAICT it was thought as architecture-specific:
> 
> /*
>   * Architectures can set this mask to a combination of PGTBL_P?D_MODIFIED values
>   * and let generic vmalloc and ioremap code know when arch_sync_kernel_mappings()
>   * needs to be called.
>   */
> #ifndef ARCH_PAGE_TABLE_SYNC_MASK
> #define ARCH_PAGE_TABLE_SYNC_MASK 0
> #endif
> 
> Not sure if that needs to be addressed at all.

Okay, if there are no users of PGTBL_PTE_MODIFIED we could just ... 
remove it. Dead code.

-- 
Cheers,

David / dhildenb