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([2a02:6b6a:b5c7:0:237f:509f:1c65:1d08]) by smtp.gmail.com with ESMTPSA id s5-20020adfdb05000000b0032d8eecf901sm11756403wri.3.2023.11.20.07.49.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 20 Nov 2023 07:49:37 -0800 (PST) Message-ID: Date: Mon, 20 Nov 2023 15:49:36 +0000 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.2 Subject: Re: 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> <454dbfa1-2120-1e40-2582-d661203decca@bytedance.com> In-Reply-To: <454dbfa1-2120-1e40-2582-d661203decca@bytedance.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: D18FB120019 X-Stat-Signature: tsamhfou819ood17gbr644daukoctgxb X-HE-Tag: 1700495381-149030 X-HE-Meta: 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 WfcPbXTG 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.022365, 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 06/11/2023 18:15, Usama Arif wrote: > 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/ > Hi, Just wanted to check if there were any comments on this? Thanks > Regards, > Usama