linux-kernel - Re: [PATCH -v2 1/2] mm: add spurious fault fixing support for huge pmd

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Message-ID: <2861a35d-4f8e-4ee1-bd11-b915580c9ce3@redhat.com>
Date: Tue, 14 Oct 2025 16:38:05 +0200
From: David Hildenbrand <david@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Huang Ying <ying.huang@...ux.alibaba.com>
Cc: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Andrew Morton <akpm@...ux-foundation.org>, Vlastimil Babka <vbabka@...e.cz>,
 Zi Yan <ziy@...dia.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Ryan Roberts <ryan.roberts@....com>, Yang Shi <yang@...amperecomputing.com>,
 "Christoph Lameter (Ampere)" <cl@...two.org>, Dev Jain <dev.jain@....com>,
 Barry Song <baohua@...nel.org>, Anshuman Khandual
 <anshuman.khandual@....com>, Yicong Yang <yangyicong@...ilicon.com>,
 Kefeng Wang <wangkefeng.wang@...wei.com>,
 Kevin Brodsky <kevin.brodsky@....com>,
 Yin Fengwei <fengwei_yin@...ux.alibaba.com>,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org
Subject: Re: [PATCH -v2 1/2] mm: add spurious fault fixing support for huge
 pmd


> 
> 		/* Skip spurious TLB flush for retried page fault */
> 		if (vmf->flags & FAULT_FLAG_TRIED)
> 			goto unlock;
> 		/*
> 		 * This is needed only for protection faults but the arch code
> 		 * is not yet telling us if this is a protection fault or not.
> 		 * This still avoids useless tlb flushes for .text page faults
> 		 * with threads.
> 		 */
> 		if (vmf->flags & FAULT_FLAG_WRITE)
> 			flush_tlb_fix_spurious_fault(vmf->vma, vmf->address,
> 						     vmf->pte);
> 
> 
> So I don't see why it's so egregious to have the equivalent here, or actually
> ideally to abstract the code entirely.

Let's definitely not duplicate such comments whereby one instance will 
end up bitrotting.

When talking about spurious faults I assume the educated reader will 
usually find the right comments -- like you easily did :P

However I agree that ...

> 
> In commit b22cc9a9c7ff ("mm/rmap: convert "enum rmap_level" to "enum
> pgtable_level"") David introduced:
> 
> 	enum pgtable_level {
> 		PGTABLE_LEVEL_PTE = 0,
> 		PGTABLE_LEVEL_PMD,
> 		PGTABLE_LEVEL_PUD,
> 		PGTABLE_LEVEL_P4D,
> 		PGTABLE_LEVEL_PGD,
> 	};
> 
> Which allows for sensible abstraction.

... if there is an easier way to just unify the code and have the 
comments at a central place, even better.

-- 
Cheers

David / dhildenb