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[2003:d8:2f18:f900:e0ae:65d5:8bf8:8cfd]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45e0153fbd5sm91804875e9.5.2025.09.15.04.08.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 15 Sep 2025 04:08:11 -0700 (PDT) Message-ID: <8c51da7a-7370-4678-96a3-7cd6eaf0db62@redhat.com> Date: Mon, 15 Sep 2025 13:08:09 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 1/2] mm: add spurious fault fixing support for huge pmd To: Huang Ying , Catalin Marinas , Will Deacon , Andrew Morton Cc: Lorenzo Stoakes , Vlastimil Babka , Zi Yan , Baolin Wang , Ryan Roberts , Yang Shi , "Christoph Lameter (Ampere)" , Dev Jain , Barry Song , Anshuman Khandual , Yicong Yang , Kefeng Wang , Kevin Brodsky , Yin Fengwei , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20250915032946.33203-1-ying.huang@linux.alibaba.com> <20250915032946.33203-2-ying.huang@linux.alibaba.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250915_040816_175686_EE5B70B5 X-CRM114-Status: GOOD ( 21.34 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 15.09.25 05:29, Huang Ying wrote: > 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 > Cc: Catalin Marinas > Cc: Will Deacon > Cc: Andrew Morton > Cc: David Hildenbrand > Cc: Lorenzo Stoakes > Cc: Vlastimil Babka > Cc: Zi Yan > Cc: Baolin Wang > Cc: Ryan Roberts > Cc: Yang Shi > Cc: "Christoph Lameter (Ampere)" > Cc: Dev Jain > Cc: Barry Song > Cc: Anshuman Khandual > Cc: Yicong Yang > Cc: Kefeng Wang > Cc: Kevin Brodsky > Cc: Yin Fengwei > Cc: linux-arm-kernel@lists.infradead.org > Cc: linux-kernel@vger.kernel.org > Cc: linux-mm@kvack.org > --- [...] > > int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm, > @@ -1857,7 +1861,20 @@ void huge_pmd_set_accessed(struct vm_fault *vmf) > if (unlikely(!pmd_same(*vmf->pmd, vmf->orig_pmd))) > goto unlock; > > - touch_pmd(vmf->vma, vmf->address, vmf->pmd, write); > + if (!touch_pmd(vmf->vma, vmf->address, vmf->pmd, write)) { > + /* 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. > + */ Can we instead just remove these comments and simplly say "see handle_pte_fault()" > + if (vmf->flags & FAULT_FLAG_WRITE) > + flush_tlb_fix_spurious_fault_pmd(vmf->vma, vmf->address, > + vmf->pmd); > + } Okay, In the PTE case, we call flush_tlb_fix_spurious_fault() during write faults if ptep_set_access_flags() returned "0". You are calling flush_tlb_fix_spurious_fault_pmd() during a write fault when pmdp_set_access_flags() returned "0" as well. In general, LGTM, but I would just let touch_pmd() return the value of pmdp_set_access_flags() instead and add a quick comment for touch_pmd() what the return value means. -- Cheers David / dhildenb