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[2003:cb:c703:d00:ca74:d9ea:11e0:dfb]) by smtp.gmail.com with ESMTPSA id f9-20020a05600c154900b003ede03e4369sm10954856wmg.33.2023.03.22.04.18.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 22 Mar 2023 04:18:09 -0700 (PDT) Message-ID: <8ba0360e-57eb-93b0-3ae6-612f6b371bff@redhat.com> Date: Wed, 22 Mar 2023 12:18:08 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.0 Subject: Re: [PATCH v4 4/4] mm: vmalloc: convert vread() to vread_iter() To: Lorenzo Stoakes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton Cc: Baoquan He , Uladzislau Rezki , Matthew Wilcox , Liu Shixin , Jiri Olsa , Jens Axboe , Alexander Viro References: <6b3899bbbf1f4bd6b7133c8b6f27b3a8791607b0.1679431886.git.lstoakes@gmail.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <6b3899bbbf1f4bd6b7133c8b6f27b3a8791607b0.1679431886.git.lstoakes@gmail.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 7ABB516000D X-Stat-Signature: mn8t9wetiafhy7o8i67hzmq3tfaggdy4 X-HE-Tag: 1679483895-660472 X-HE-Meta: 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 HJPeP8co BQhVjPlsfWN/l+kYtVeyyZkDKLgYsM+tcXcalJTMT7trt1wOn9sJiC/LAjR3N13VgrnnzsGPFFyLvU72jwZjWlnRTqQYzE2oJWUu+dYqlWjj0xdKblzhdAT1l+IWZYczAZukcyHzkX598m0jvv31t5X89xPTFZNhBVC7pqI42kj6+xC2ap/+2Q2CQF3rRZj1iHO50NNEffkionXzXGjjxNlESts0ZbtW7EHZPSzCJCptyObf6IBc0Izv+/s17E4FJtmpH/IPSnnsdsMgs3C3+FtT05yUo/5evqZrMHrNnRSTvxaQWvYQUeXcZAJIVvBIx8ojZYmuq1q79WFELGLITutKJ08ZslrTIDpsbqmO9RHR5APC5n5H5fk+n52o2G5LrcyYp099osGR9TMnEhVg4sGcuFm/V9tTc+ZSe57BJh2Ddk7vuJb2sICtn6WdUH34tGxYIPY076zjJjX0ogTXDghwuvOszhwm8naGt 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 21.03.23 21:54, Lorenzo Stoakes wrote: > Having previously laid the foundation for converting vread() to an iterator > function, pull the trigger and do so. > > This patch attempts to provide minimal refactoring and to reflect the > existing logic as best we can, for example we continue to zero portions of > memory not read, as before. > > Overall, there should be no functional difference other than a performance > improvement in /proc/kcore access to vmalloc regions. > > Now we have eliminated the need for a bounce buffer in read_kcore_iter(), > we dispense with it. We need to ensure userland pages are faulted in before > proceeding, as we take spin locks. > > Additionally, we must account for the fact that at any point a copy may > fail if this happens, we exit indicating fewer bytes retrieved than > expected. > > Signed-off-by: Lorenzo Stoakes > --- > fs/proc/kcore.c | 26 ++--- > include/linux/vmalloc.h | 3 +- > mm/nommu.c | 10 +- > mm/vmalloc.c | 234 +++++++++++++++++++++++++--------------- > 4 files changed, 160 insertions(+), 113 deletions(-) > > diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c > index 25e0eeb8d498..221e16f75ba5 100644 > --- a/fs/proc/kcore.c > +++ b/fs/proc/kcore.c > @@ -307,13 +307,9 @@ static void append_kcore_note(char *notes, size_t *i, const char *name, > *i = ALIGN(*i + descsz, 4); > } > > -static ssize_t > -read_kcore_iter(struct kiocb *iocb, struct iov_iter *iter) > +static ssize_t read_kcore_iter(struct kiocb *iocb, struct iov_iter *iter) > { > - struct file *file = iocb->ki_filp; > - char *buf = file->private_data; > loff_t *ppos = &iocb->ki_pos; > - > size_t phdrs_offset, notes_offset, data_offset; > size_t page_offline_frozen = 1; > size_t phdrs_len, notes_len; > @@ -507,9 +503,12 @@ read_kcore_iter(struct kiocb *iocb, struct iov_iter *iter) > > switch (m->type) { > case KCORE_VMALLOC: > - vread(buf, (char *)start, tsz); > - /* we have to zero-fill user buffer even if no read */ > - if (copy_to_iter(buf, tsz, iter) != tsz) { > + /* > + * Make sure user pages are faulted in as we acquire > + * spinlocks in vread_iter(). > + */ > + if (fault_in_iov_iter_writeable(iter, tsz) || > + vread_iter(iter, (char *)start, tsz) != tsz) { > ret = -EFAULT; > goto out; > } What if we race with swapout after faulting the pages in? Or some other mechanism to write-protect the user space pages? Also, "This is primarily useful when we already know that some or all of the pages in @i aren't in memory". This order of events might slow down things quite a bit if I am not wrong. Wouldn't you want to have something like: while (vread_iter(iter, (char *)start, tsz) != tsz) { if (fault_in_iov_iter_writeable(iter, tsz)) { ret = -EFAULT; goto out; } } Or am I missing something? -- Thanks, David / dhildenb