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

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Message-ID: <aFpxvQxgUEdO9jd/@li-008a6a4c-3549-11b2-a85c-c5cc2836eea2.ibm.com>
Date: Tue, 24 Jun 2025 11:37:01 +0200
From: Alexander Gordeev <agordeev@...ux.ibm.com>
To: David Hildenbrand <david@...hat.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 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.

> -- 
> Cheers,
> 
> David / dhildenb

Thanks!