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Sat, 15 Apr 2023 04:48:01 -0700 (PDT) Date: Sat, 15 Apr 2023 12:48:00 +0100 From: Lorenzo Stoakes To: Tetsuo Handa Cc: Andrew Morton , linux-mm@kvack.org Subject: Re: [PATCH v2 3/7] mm/gup: remove vmas parameter from get_user_pages_remote() Message-ID: References: <631001ecc556c5e348ff4f47719334c31f7bd592.1681547405.git.lstoakes@gmail.com> <63d92734-2185-439c-bbc7-53a4720f5d4a@lucifer.local> <65e79cf8-8713-4d2d-7a50-76d7e2aa454a@I-love.SAKURA.ne.jp> <64ae6557-0e46-48a8-badd-af8993645330@lucifer.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 4BCDF40019 X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: qww1gjddydrc87nex5q6jeeau5wwruq6 X-HE-Tag: 1681559284-197765 X-HE-Meta: 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 pVLDqb7D 2kYSmEInSn85X5c0nbBv8d8gNMNUgBBt22WPxnMcGYcixtWsHgSvD7KWkmq0NQLRANyoKR6COLK5w4KMBxRtsxjXQ1r6ZEAmgHGWbg1RvCWi4ij2QmgAd8VQ1SfCh3e/nQlBfB0bZtxmMHQdMPJaGVSQCchjSNsAlvLzziAj0269msVZr7LAYtIn+u2WGrEe9PEMzz4prwmg18TrpUC10p26aCUnAeuP00E8VC9uS4J6mcIaVm1eVfwPs9xeVtBMrOxz/R/SKXVIk0xiXbPvNWDmBYHAvj3U/Zdc+lsA8OicjLabfQr4r8oYyOE4wXc9ARTe2A+9GKmwt500ylRUSBzVmK+EMYHmmBJ85+gzfcpsm/S/dwOYg44MhwfUcKGrTXMDawp/Qcz/mfmJm9SkLc/heDKU1huM2t6bjWjGocakL3xF4Rr1GCY2BrXcHNSjUOSC3+r1ePfi9GEU= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sat, Apr 15, 2023 at 08:40:44PM +0900, Tetsuo Handa wrote: > On 2023/04/15 20:27, Lorenzo Stoakes wrote: > >>> @@ -5617,11 +5618,11 @@ int __access_remote_vm(struct mm_struct *mm, unsigned long addr, void *buf, > >>> bytes = PAGE_SIZE-offset; > >>> > >>> maddr = kmap(page); > >>> - if (write) { > >>> + if (write && vma) { > >>> copy_to_user_page(vma, page, addr, > >>> maddr + offset, buf, bytes); > >>> set_page_dirty_lock(page); > >>> - } else { > >>> + } else if (vma) { > >>> copy_from_user_page(vma, page, addr, > >>> buf, maddr + offset, bytes); > >>> } > >> > >> not calling copy_{from,to}_user_page() if vma == NULL is not sufficient for > >> propagating an error to caller. > >> > > > > This is a product of wanting to avoid churn, again this condition is simply > > impossible. Also as a pedantic side note - the loop explicitly indicates no > > errors are propagated, so there is no need to do so. > > Since __access_remote_vm() implicitly indicates an error via "return buf - old_buf;", > "buf += bytes;" must not be executed if copy_{to,from}_user_page(bytes) was not called. > > Yes, indeed, perhaps I wasn't clear, ack that we shouldn't increment buf if !vma, I already fixed this in the respin and additionally have added a warning here and in every instance of unexpected !vma. Will spam everybody with v3 once the allmodconfig build is complete... :)