linux-kernel - Re: [PATCH -v3 1/2] mm: add spurious fault fixing support for huge pmd

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Message-ID: <ff869b97-22bb-48af-b109-ca096afed7b7@redhat.com>
Date: Fri, 24 Oct 2025 17:57:23 +0200
From: David Hildenbrand <david@...hat.com>
To: Huang Ying <ying.huang@...ux.alibaba.com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 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>, 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 -v3 1/2] mm: add spurious fault fixing support for huge
 pmd

On 23.10.25 03:35, Huang Ying wrote:
> The page faults may be spurious because of the racy access to the page
> table.  For example, a non-populated virtual page is accessed on 2
> CPUs simultaneously, thus the page faults are triggered on both CPUs.
> However, it's possible that one CPU (say CPU A) cannot find the reason
> for the page fault if the other CPU (say CPU B) has changed the page
> table before the PTE is checked on CPU A.  Most of the time, the
> spurious page faults can be ignored safely.  However, if the page
> fault is for the write access, it's possible that a stale read-only
> TLB entry exists in the local CPU and needs to be flushed on some
> architectures.  This is called the spurious page fault fixing.
> 
> In the current kernel, there is spurious fault fixing support for pte,
> but not for huge pmd because no architectures need it. But in the
> next patch in the series, we will change the write protection fault
> handling logic on arm64, so that some stale huge pmd entries may
> remain in the TLB. These entries need to be flushed via the huge pmd
> spurious fault fixing mechanism.
> 
> Signed-off-by: Huang Ying <ying.huang@...ux.alibaba.com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: Zi Yan <ziy@...dia.com>
> Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Cc: Ryan Roberts <ryan.roberts@....com>
> Cc: Yang Shi <yang@...amperecomputing.com>
> Cc: "Christoph Lameter (Ampere)" <cl@...two.org>
> Cc: Dev Jain <dev.jain@....com>
> Cc: Barry Song <baohua@...nel.org>
> Cc: Anshuman Khandual <anshuman.khandual@....com>
> Cc: Kefeng Wang <wangkefeng.wang@...wei.com>
> Cc: Kevin Brodsky <kevin.brodsky@....com>
> Cc: Yin Fengwei <fengwei_yin@...ux.alibaba.com>
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-mm@...ck.org
> ---

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers

David / dhildenb