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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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <56c982c4-9863-4134-b088-8dfb4b94c531@redhat.com> 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