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[99.254.121.117]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6b7ac7f15d3sm50461336d6.67.2024.07.23.13.27.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 23 Jul 2024 13:27:48 -0700 (PDT) Date: Tue, 23 Jul 2024 16:27:44 -0400 From: Peter Xu To: David Hildenbrand Cc: Yan Zhao , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , Andrew Morton , Alex Williamson , Jason Gunthorpe , Al Viro , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "Kirill A . Shutemov" , "x86@kernel.org" , "Tian, Kevin" , Pei Li , David Wang <00107082@163.com>, Bert Karwatzki , Sergey Senozhatsky Subject: Re: [PATCH] mm/x86/pat: Only untrack the pfn range if unmap region Message-ID: References: <1a0884cb-39ed-455e-a505-7c1b2a0e5225@redhat.com> <56c982c4-9863-4134-b088-8dfb4b94c531@redhat.com> MIME-Version: 1.0 In-Reply-To: <56c982c4-9863-4134-b088-8dfb4b94c531@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 631082001A X-Stat-Signature: 49qxk7e3z7e7errt7cyxsb8z1w11pbkq X-Rspam-User: X-HE-Tag: 1721766474-534547 X-HE-Meta: U2FsdGVkX1/nqSfIClYreiR7Wjhb4E6QXs9EMAMsgMfFP3t8XRhryPFge5yO78BuUpjSBmrzQU8KnOcGmSuOHvavxsycYKudp/ThfClqawx/kQAo0z6HRgIVc/2CSesdPQIrqcENdFZ63gIKGStQyjacqyLQT11o5MVezRDuJGL5PV8e2/tAyScZorxLRbVHZPrBkuFIARHdu+ZRGxVeB3U3XmUv9lICZ/+wrUleuCeYHzeV+6BEEpJQhXEX6Yz2ae6bfarPFWqrTuOpCn6Dg6+wgbd04Y88YEH2AfTxIQ0xhUDuljsXy1NemHZSD0If6FTBBov41ftFqKYoR+L6q3XqhITJSdvhxDN6zQ8msVWKGpKDcBp/4dnzF5Pln5h05XGCLFk1JBVreXFZpP6R6L2yJndwO92kkr1mbtEy1ioyesSctKP7M/xwv+B5V+TAomzmXNjcYe1EJZ9XV5RGPy6owZufz+FnMxDh6dx4cOP+c5wNi7ywC9XNcZRiK0InawOtZoRiYvpOeToGjNkWsmlHdKWKAtO1PYtHTuGQEVjImFUuAQ8HTafkCxmtF7xJhNcVnWO3GwM1rsDcAfe67Xjq3HJGp+CJw+Qvn6RA1f0j+ot6Zkn6Ov/6ESJHXK1JQXQdXzEbpu203uU+NqN34VUkTFTgStTPSDU0zZ3K40Fbse+6I9Bsa6poSEztbZs+mKuPQT+OgjA6kbezWkzAuEmUvby3aXMSM3UJbZiLf4S1CpyLqWLAiT/oNyzElCDZzpu/rCgGFuQ8wM81s1bFd15jQw9q0R0OZs3OKcjhs806QZd4H9p7LLuPTPQnMVeS4XFyb4sBlZwXOM4Mz4HEbX1CmyhDuNndtlRe3xUGAb3FSFTykuRk85wObqvng5LtnmEvq220cC05rOfcHerzbk3bnN7mcESD9hDxwXMpALMoRnsUsPSz2rt7e9P7jVu2pRgJk4VkEfyNULe2rAI YX/SwLp+ FawrhrpIMjJIGtvuf/ZLEgxarNC3yjE/QxDOPd2804uNUprFiolwCShnkRW0BLAZz/XiMKx/P9pJEHyxeae6kTUaIZW11TxI2Zy25WPXThIn1vtZCg46udmlBQ/z9c8MnntT9WORvfwVosEEc6J/eUaH8K0NNqHZMeiaRr5uXZJjocaVn67qMHKu06nX+t36+fM+l8ETyjieAn2YLIr3UeymJXqehCsFQ1mTo8gsC1i6e/T1wQ8+YsznwPk2XRoNG5Hb7BNuLdnzqF+jjaiU/QWeZOOISFhKZg7uZVhq1HJX+3SXhq2037kzYjAJ3kVoANSy5FfCU6Zajg8aFjzXkIZDD98D5fe0oNy83fgkri2WRddbS7uW2/3auPuRrv+z7D/7fC+hdh04KJEFW5mEhpKNaugIsg24svXR7GNOUDQKYoU58b12AQpbg8p2FulCGYJorlucA6Fx0a0VlrqKdahhhZQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Jul 22, 2024 at 11:17:57AM +0200, David Hildenbrand wrote: > What we do have is a single VMA, whereby within that VMA we place various > different PFN ranges. (randomly looking at drivers/video/fbdev/smscufx.c) > > These wouldn't have triggered VM_PAT code. Right, it looks like VM_PAT is only applying to a whole-vma mapping, even though I don't know how that was designed.. I wished vma->vm_pgoff was for storing the base PFN for VM_SHARED too: now it only works like that for CoW mappings in remap_pfn_range_notrack(), then it looks like VM_SHARED users of remap_pfn_range() can reuse vm_pgoff, and I think VFIO does reuse it at least.. I am a bit confused on why Linux made that different for VM_SHARED, probably since b3b9c2932c32 ("mm, x86, pat: rework linear pfn-mmap tracking"). I wished vm_pgoff was always used for internal maintenance (even for VM_SHARED) so this issue should be easier to solve. Maybe we can still re-define vm_pgoff for VM_SHARED pfnmaps? The caller should always be able to encode information in vm_private_data anyway. But I think that might break OOT users.. -- Peter Xu