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[99.254.144.39]) by smtp.gmail.com with ESMTPSA id s24-20020a05620a16b800b007743446efd1sm3252625qkj.35.2023.09.28.11.43.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 28 Sep 2023 11:43:54 -0700 (PDT) Date: Thu, 28 Sep 2023 14:43:51 -0400 From: Peter Xu To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, viro@zeniv.linux.org.uk, brauner@kernel.org, shuah@kernel.org, aarcange@redhat.com, lokeshgidra@google.com, david@redhat.com, hughd@google.com, mhocko@suse.com, axelrasmussen@google.com, rppt@kernel.org, willy@infradead.org, Liam.Howlett@oracle.com, jannh@google.com, zhangpeng362@huawei.com, bgeffon@google.com, kaleshsingh@google.com, ngeoffray@google.com, jdduke@google.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v2 2/3] userfaultfd: UFFDIO_REMAP uABI Message-ID: References: <20230923013148.1390521-1-surenb@google.com> <20230923013148.1390521-3-surenb@google.com> MIME-Version: 1.0 In-Reply-To: <20230923013148.1390521-3-surenb@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 866A1140019 X-Stat-Signature: thtz1m79u8duaa9f18bankkbp7r95ko9 X-Rspam-User: X-HE-Tag: 1695926637-910709 X-HE-Meta: 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 iTjg1O2l 5+KrEDfwKnBPCErW75Ol8ZCqirM5mFozRUhwotRw7//SyUeRJI/IXE/VIAhsaTB0DC6XeYQzMkRzb2Rpk5Hb6w1GhtvoWzJIYGgzsW8k5Mqbub7hdOiVLH18Q70UdkCUaSvHjm01uWsEyx4NyFDar/MWrGG97bjo7Iv6r5WhIfOq3TzGu1NAiBc0NZmhODLEIbMBN0C0SyvVI6cMv2IVoEI6W8xoJXS23z2QG9/jonw+j+qBRE+mZG40I12dk98L3ydkAEECjk2YkjBZyHrqZbosuUKRnrPcCPpbhOr8gGo4auHosEnl8ZJ2rilJJnRHsESAITMiooDj6bdZN7GmPAm7u1ewwg+MjmOMcvYgSKPqHZxfgIztcPoCi/2AgyUCz862fQRHA6UfRcU8NqCi2QmYqZw0mruaEJm1+ 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: One more thing.. On Fri, Sep 22, 2023 at 06:31:45PM -0700, Suren Baghdasaryan wrote: > +static int remap_pages_pte(struct mm_struct *dst_mm, [...] > +retry: > + dst_pte = pte_offset_map_nolock(dst_mm, dst_pmd, dst_addr, &dst_ptl); > + > + /* If an huge pmd materialized from under us fail */ > + if (unlikely(!dst_pte)) { > + err = -EFAULT; > + goto out; > + } > + > + src_pte = pte_offset_map_nolock(src_mm, src_pmd, src_addr, &src_ptl); > + > + /* > + * We held the mmap_lock for reading so MADV_DONTNEED > + * can zap transparent huge pages under us, or the > + * transparent huge page fault can establish new > + * transparent huge pages under us. > + */ > + if (unlikely(!src_pte)) { > + err = -EFAULT; > + goto out; > + } For these two places: I know that thp collapse with mmap read lock hasn't yet spread to anon (so I assume none of above could trigger yet on the failure paths), but shall we constantly return -EAGAIN here just in case we forget that in the future? For example, for UFFDIO_COPY over shmem which we can already hit similar case, mfill_atomic_install_pte() has: ret = -EAGAIN; dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl); if (!dst_pte) goto out; Thanks, -- Peter Xu