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Hallyn" , Paolo Bonzini , Jens Axboe , Pavel Begunkov , Jason Gunthorpe , John Hubbard Subject: Re: [PATCH v5 3/6] mm/gup: remove vmas parameter from get_user_pages_remote() Message-Id: <20230516150218.477c5e9d0a2d9ef8b057069c@linux-foundation.org> In-Reply-To: <20230516094919.GA411@mutt> References: <20230516094919.GA411@mutt> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: B679B80011 X-Stat-Signature: bnnmkw1yb6zdf9g6xf5uazt8eopg6tc3 X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1684274541-377934 X-HE-Meta: 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 f3YpMoGJ 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 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 Tue, 16 May 2023 11:49:19 +0200 Anders Roxell wrote: > On 2023-05-14 22:26, Lorenzo Stoakes wrote: > > The only instances of get_user_pages_remote() invocations which used the > > vmas parameter were for a single page which can instead simply look up the > > VMA directly. In particular:- > > > > - __update_ref_ctr() looked up the VMA but did nothing with it so we simply > > remove it. > > > > - __access_remote_vm() was already using vma_lookup() when the original > > lookup failed so by doing the lookup directly this also de-duplicates the > > code. > > > > We are able to perform these VMA operations as we already hold the > > mmap_lock in order to be able to call get_user_pages_remote(). > > > > As part of this work we add get_user_page_vma_remote() which abstracts the > > VMA lookup, error handling and decrementing the page reference count should > > the VMA lookup fail. > > > > This forms part of a broader set of patches intended to eliminate the vmas > > parameter altogether. > > > > - int bytes, ret, offset; > > + int bytes, offset; > > void *maddr; > > - struct page *page = NULL; > > + struct vm_area_struct *vma; > > + struct page *page = get_user_page_vma_remote(mm, addr, > > + gup_flags, &vma); > > + > > + if (IS_ERR_OR_NULL(page)) { > > + int ret = 0; > > I see the warning below when building without CONFIG_HAVE_IOREMAP_PROT set. > > make --silent --keep-going --jobs=32 \ > O=/home/anders/.cache/tuxmake/builds/1244/build ARCH=arm \ > CROSS_COMPILE=arm-linux-gnueabihf- /home/anders/src/kernel/next/mm/memory.c: In function '__access_remote_vm': > /home/anders/src/kernel/next/mm/memory.c:5608:29: warning: unused variable 'ret' [-Wunused-variable] > 5608 | int ret = 0; > | ^~~ Thanks, I did the obvious. Also s/ret/res/, as `ret' is kinda reserved for "this is what this function will return". --- a/mm/memory.c~mm-gup-remove-vmas-parameter-from-get_user_pages_remote-fix +++ a/mm/memory.c @@ -5605,11 +5605,11 @@ int __access_remote_vm(struct mm_struct gup_flags, &vma); if (IS_ERR_OR_NULL(page)) { - int ret = 0; - #ifndef CONFIG_HAVE_IOREMAP_PROT break; #else + int res = 0; + /* * Check if this is a VM_IO | VM_PFNMAP VMA, which * we can access using slightly different code. @@ -5617,11 +5617,11 @@ int __access_remote_vm(struct mm_struct if (!vma) break; if (vma->vm_ops && vma->vm_ops->access) - ret = vma->vm_ops->access(vma, addr, buf, + res = vma->vm_ops->access(vma, addr, buf, len, write); - if (ret <= 0) + if (res <= 0) break; - bytes = ret; + bytes = res; #endif } else { bytes = len; _