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Tue, 09 Jul 2024 21:07:16 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHVPYdr4bPLEq6M4tEtg9rbxzBv1IyFaW+LEhahGAul2R/CZttE0zE6k2ed4WL4HvkfL/CfIg== X-Received: by 2002:a17:902:ec8a:b0:1fb:9b91:d7db with SMTP id d9443c01a7336-1fbb6d3d3b6mr44601915ad.19.1720584435800; Tue, 09 Jul 2024 21:07:15 -0700 (PDT) Received: from [172.20.2.228] ([4.28.11.157]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-1fbb6ab7d38sm23489205ad.137.2024.07.09.21.07.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 09 Jul 2024 21:07:15 -0700 (PDT) Message-ID: Date: Wed, 10 Jul 2024 06:07:13 +0200 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: Fix PTE_AF handling in fault path on architectures with HW AF support To: Ram Tummala , akpm@linux-foundation.org, fengwei.yin@intel.com Cc: willy@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, apopple@nvidia.com, stable@vger.kernel.org References: <20240710000942.623704-1-rtummala@nvidia.com> Content-Language: en-US From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 10.07.24 02:09, Ram Tummala wrote: > Commit 3bd786f76de2 ("mm: convert do_set_pte() to set_pte_range()") > replaced do_set_pte() with set_pte_range() and that introduced a regression > in the following faulting path of non-anonymous vmas on CPUs with HW AF > support. > > handle_pte_fault() > do_pte_missing() > do_fault() > do_read_fault() || do_cow_fault() || do_shared_fault() > finish_fault() > set_pte_range() > > The polarity of prefault calculation is incorrect. This leads to prefault > being incorrectly set for the faulting address. The following if check will > incorrectly clear the PTE_AF bit instead of setting it and the access will > fault again on the same address due to the missing PTE_AF bit. > > if (prefault && arch_wants_old_prefaulted_pte()) > entry = pte_mkold(entry); > > On a subsequent fault on the same address, the faulting path will see a non > NULL vmf->pte and instead of reaching the do_pte_missing() path, PTE_AF > will be correctly set in handle_pte_fault() itself. > > Due to this bug, performance degradation in the fault handling path will be > observed due to unnecessary double faulting. > > Cc: stable@vger.kernel.org > Fixes: 3bd786f76de2 ("mm: convert do_set_pte() to set_pte_range()") > Signed-off-by: Ram Tummala > --- Acked-by: David Hildenbrand -- Cheers, David / dhildenb