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Tue, 15 Feb 2022 21:50:47 +0000 Received: from BY5PR12MB4130.namprd12.prod.outlook.com ([fe80::498:6469:148a:49c7]) by BY5PR12MB4130.namprd12.prod.outlook.com ([fe80::498:6469:148a:49c7%6]) with mapi id 15.20.4995.015; Tue, 15 Feb 2022 21:50:47 +0000 Message-ID: <487fdaad-0873-142a-cf3a-a065bc8acff6@nvidia.com> Date: Tue, 15 Feb 2022 13:50:44 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.0 Subject: Re: [PATCH v2 1/3] migrate.c: Remove vma check in migrate_vma_setup() Content-Language: en-US To: Alistair Popple , akpm@linux-foundation.org, linux-mm@kvack.org Cc: Felix.Kuehling@amd.com, rcampbell@nvidia.com, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, hch@lst.de, jgg@nvidia.com, jglisse@redhat.com, willy@infradead.org, alex.sierra@amd.com References: <6831bf69f7c7699be83b31c9c56212b5fb07f873.1644207242.git-series.apopple@nvidia.com> From: John Hubbard In-Reply-To: <6831bf69f7c7699be83b31c9c56212b5fb07f873.1644207242.git-series.apopple@nvidia.com> Content-Type: text/plain; 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dkim=pass header.d=Nvidia.com header.s=selector2 header.b=sH+AFfr5; spf=none (imf07.hostedemail.com: domain of jhubbard@nvidia.com has no SPF policy when checking 40.107.223.83) smtp.mailfrom=jhubbard@nvidia.com; dmarc=pass (policy=reject) header.from=nvidia.com X-HE-Tag: 1644961849-971872 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 2/6/22 20:26, Alistair Popple wrote: > migrate_vma_setup() checks that a valid vma is passed so that the page > tables can be walked to find the pfns associated with a given address > range. However in some cases the pfns are already known, such as when > migrating device coherent pages during pin_user_pages() meaning a valid > vma isn't required. > > Signed-off-by: Alistair Popple > Acked-by: Felix Kuehling > --- > > Changes for v2: > > - Added Felix's Acked-by > > mm/migrate.c | 34 +++++++++++++++++----------------- > 1 file changed, 17 insertions(+), 17 deletions(-) > Hi Alistair, Another late-breaking review question, below. :) > diff --git a/mm/migrate.c b/mm/migrate.c > index a9aed12..0d6570d 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -2602,24 +2602,24 @@ int migrate_vma_setup(struct migrate_vma *args) > > args->start &= PAGE_MASK; > args->end &= PAGE_MASK; > - if (!args->vma || is_vm_hugetlb_page(args->vma) || > - (args->vma->vm_flags & VM_SPECIAL) || vma_is_dax(args->vma)) > - return -EINVAL; > - if (nr_pages <= 0) > - return -EINVAL; Was the above check left out intentionally? If so, then it needs a commit description note. And maybe even a separate patch, because it changes the behavior. If you do want to change the behavior: * The kerneldoc comment above this function supports such a change: it requires returning 0 for the case of zero pages requested. So your change would bring the comments into alignment with the code. * I don't think memset deals properly with a zero length input arg, so it's probably better to return 0, before that point. thanks, -- John Hubbard NVIDIA > - if (args->start < args->vma->vm_start || > - args->start >= args->vma->vm_end) > - return -EINVAL; > - if (args->end <= args->vma->vm_start || args->end > args->vma->vm_end) > - return -EINVAL; > if (!args->src || !args->dst) > return -EINVAL; > - > - memset(args->src, 0, sizeof(*args->src) * nr_pages); > - args->cpages = 0; > - args->npages = 0; > - > - migrate_vma_collect(args); > + if (args->vma) { > + if (is_vm_hugetlb_page(args->vma) || > + (args->vma->vm_flags & VM_SPECIAL) || vma_is_dax(args->vma)) > + return -EINVAL; > + if (args->start < args->vma->vm_start || > + args->start >= args->vma->vm_end) > + return -EINVAL; > + if (args->end <= args->vma->vm_start || args->end > args->vma->vm_end) > + return -EINVAL; > + > + memset(args->src, 0, sizeof(*args->src) * nr_pages); > + args->cpages = 0; > + args->npages = 0; > + > + migrate_vma_collect(args); > + } > > if (args->cpages) > migrate_vma_unmap(args); > @@ -2804,7 +2804,7 @@ void migrate_vma_pages(struct migrate_vma *migrate) > continue; > } > > - if (!page) { > + if (!page && migrate->vma) { > if (!(migrate->src[i] & MIGRATE_PFN_MIGRATE)) > continue; > if (!notified) {