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(p200300cbc70737003eeaace65bde4478.dip0.t-ipconnect.de. [2003:cb:c707:3700:3eea:ace6:5bde:4478]) by smtp.gmail.com with ESMTPSA id 12-20020a05600c020c00b003f819faff24sm16034728wmi.40.2023.07.12.08.55.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 12 Jul 2023 08:55:48 -0700 (PDT) Message-ID: <331201b2-5f13-8e81-b5d4-b17f8784d498@redhat.com> Date: Wed, 12 Jul 2023 17:55:47 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Subject: Re: [bug report] mm: replace vma->vm_flags direct modifications with modifier calls To: Matthew Wilcox , Suren Baghdasaryan Cc: Dan Carpenter , linux-mm@kvack.org, Andrew Morton , "Liam R. Howlett" , Laurent Dufour , Michel Lespinasse , Jerome Glisse , Michal Hocko , Vlastimil Babka , Johannes Weiner , Peter Xu , Dimitri Sivanich , Mike Travis , Steve Wahl References: <9704a138-60e6-4ede-91f0-844e1df2ad84@moroto.mountain> From: David Hildenbrand Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 5479B100023 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: k41wwnurdqoc3mccaihmh37rwpq69933 X-HE-Tag: 1689177353-347986 X-HE-Meta: U2FsdGVkX19NeDwo1bKCxYaIDZoIXqmsJ2vNiwGnaHIsasNBweWaAbtmGPj61ZODy+nLRNlXIg2V43iOmfX5y4y12pf1eswE8gIuoAL+WSnxevJ3UiappZZFTC6XlYfDAhyVmzJvB8nxLvRBfRX6zLM+OXz0cqQ+o+Qy57QSZ53VVfY1zYXuWujNqAczke+d/Pri5zX17sQCA5Ee2eM9W9GosxfseHa4FdlahCYMg8Q1UqEEn8D6/fTxfvFExNW9VbH+rlkA2E+et3BuEPfpwWhFSLpsOYME30cF3Yco41ky7Mp1PhhGom7+ktbG6mLOdRYaiH/Did44lVFJrC1Yk8MMvZZLvGkmpJg5wdHX7jvi1xDLa2QtcHuJsaZcIjsFxGqfw5EtJ8TlAeNDjFhXUn2lOyacOtN3+cauEzHVF46+eorNDGCcIN/0MZXGvuPpcbjb/Y26EkgVHf9KoN+kRaB5LP4Da2pWF3EtwmppyezQBvfhgAEqZ7oxdFkJ4jEW7heANp27IOKzfkAt+ZCz4d8TR8Qpo/0AD/ZTy1BtQIMaVt6KP6OyQjH88FC66vgBPP6P5A8kdkwLiUWf1EZFScRD/x0WzGFebLp1dcdas1sEtvdHmkM+3cqhGFXOcHBbSK0qxItpuEK65uin+j6Z9dy2e8nSnW/V4U1QkdQGByHaSw1gReCapc6dlbXFepquIq0D8imcdHCeojNJRqMhr/hMqsC/DllDpPj8O3Q+a9XYzNjJ7z6UVHit0ljKcSa3JyZMTIjKSXZ8sVPK2gB1H53Qt2Xb7VG/vUnhJh8KQZhQhbW2WnTnSsVG+fsrH8Yr+Vw+BJPm7thWEpVhV/FgJaRYa/6NUPgIlnr7Ea80GFjr1QeoNf0RlRsIYlus6l8embKH3s+J9QqDZT8KLVyIxtK7mt6sTe8EpfiIKQkkvrG/6SKPQXhxrq76TYgG0Q+A4UhfzN106CpzyI1GtCr NhqfS7QB ibY4hgt0y4Os40A3GNX32bFwg5Xp1xOUdRDFpQb/B0GiEScP5y2V2BxmmH4Ajj1n5R4WCQq/lNwkM8pSt2PjuOrf535T34zS/OZpi+K+WANLXPQn2ILVo58oSq6THXLD5wgW4tjmJgQM+8DYpug9W0zYC+oAX5iRGzm5uDBMKgrvgPEEUjrHdi3zoYVxLTDXTXVk6rAZlt2ziFsgGXh8AuEQIjfYbfZcDu9LU7xYWxtzkgSqtufWsj132UrJrFzrCPmK5XI1GURcY0VEL69pPcimCTVwNovqvcfHk6+d0tkr+uNf7vpYfX93MAPYJarIkIQ6Sc9QVQVIdq89f9qSbjsVdK/HjLtkTrKDHM1J7p5UJpENekuJeykaFsKkbWb6rC2N0YI8Sm0TT0hEWPtCaz1BQUpk40el8ILRMpyTNM7yVLykhbX/Jbqsnnw== 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: On 12.07.23 17:52, Matthew Wilcox wrote: > On Wed, Jul 12, 2023 at 08:01:18AM -0700, Suren Baghdasaryan wrote: >> Are you suggesting to break remap_pfn_range() into two stages >> (remap_pfn_range_prepare() then remap_pfn_range())? >> If so, there are many places remap_pfn_range() is called and IIUC all >> of them would need to use that 2-stage approach (lots of code churn). >> In addition, this is an exported function, so many more drivers might >> expect the current behavior. > > You do not understand correctly. > > When somebody calls mmap, there are two reasonable implementations. > Here's one: > > .mmap = snd_dma_iram_mmap, > > static int snd_dma_iram_mmap(struct snd_dma_buffer *dmab, > struct vm_area_struct *area) > { > area->vm_page_prot = pgprot_writecombine(area->vm_page_prot); > return remap_pfn_range(area, area->vm_start, > dmab->addr >> PAGE_SHIFT, > area->vm_end - area->vm_start, > area->vm_page_prot); > } > > This is _fine_. It is not called from the fault path, it is called in > process context. Few locks are held (which ones aren't even > documented!) > > The other way is to set vma->vm_ops. The fault handler in vm_ops > should not be calling remap_pfn_range(). It should be calling > set_ptes(). I almost have this driver fixed up, but I have another > meeting to go to now. Just a note that we still have to make sure that the VMA flags will be set properly -- I guess at mmap time is the right time as I suggested above. -- Cheers, David / dhildenb