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([2a02:6b6a:b5c7:0:cc4:fc61:ba1d:d46c]) by smtp.gmail.com with ESMTPSA id v6-20020a05600c444600b0040651505684sm13125607wmn.29.2023.11.06.10.15.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 06 Nov 2023 10:15:40 -0800 (PST) Message-ID: <454dbfa1-2120-1e40-2582-d661203decca@bytedance.com> Date: Mon, 6 Nov 2023 18:15:39 +0000 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.2 Subject: Conditions for FOLL_LONGTERM mapping in fsdax Content-Language: en-US From: Usama Arif To: dan.j.williams@intel.com, vishal.l.verma@intel.com, dave.jiang@intel.com, nvdimm@lists.linux.dev Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Fam Zheng , "liangma@liangbit.com" References: <172ab047-0dc7-1704-5f30-ec7cd3632e09@bytedance.com> In-Reply-To: <172ab047-0dc7-1704-5f30-ec7cd3632e09@bytedance.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: wckgf6ozokxeuu4s1zkh16xr58wr99j3 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: EB84540015 X-Rspam-User: X-HE-Tag: 1699294542-130406 X-HE-Meta: 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 MNNb+vZs 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000008, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi, We wanted to run a VM with a vfio device assigned to it and with its memory-backend-file residing in a persistent memory using fsdax (mounted as ext4). It doesnt currently work with the kernel as vfio_pin_pages_remote ends up requesting pages with FOLL_LONGTERM which is currently not supported. From reading the mailing list, what I understood was that this is to do with not having DMA supported on fsdax due to issues that come up during truncate/hole-punching. But it was solved with [1] by deferring fallocate(), truncate() on a dax mode file while any page/block in the file is under active DMA. If I remove the check which fails the gup opertion with the below diff, the VM boots and the vfio device works without any issues. If I try to truncate the mem file in fsdax, I can see that the truncate command gets deferred (waits in ext4_break_layouts) and the vfio device keeps working and sending packets without any issues. Just wanted to check what is missing to allow FOLL_LONGTERM gup operations with fsdax? Is it just enough to remove the check? Thanks! diff --git a/mm/gup.c b/mm/gup.c index eb8d7baf9e4d..f77bb428cf9b 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1055,9 +1055,6 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags) if (gup_flags & FOLL_ANON && !vma_is_anonymous(vma)) return -EFAULT; - if ((gup_flags & FOLL_LONGTERM) && vma_is_fsdax(vma)) - return -EOPNOTSUPP; - if (vma_is_secretmem(vma)) return -EFAULT; [1] https://lore.kernel.org/all/152669371377.34337.10697370528066177062.stgit@dwillia2-desk3.amr.corp.intel.com/ Regards, Usama