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[86.146.209.214]) by smtp.gmail.com with ESMTPSA id p11-20020a05600c1d8b00b003daffc2ecdesm21600525wms.13.2023.03.21.23.19.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Mar 2023 23:19:35 -0700 (PDT) Date: Wed, 22 Mar 2023 06:17:24 +0000 From: Lorenzo Stoakes To: Baoquan He Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton , Uladzislau Rezki , Matthew Wilcox , David Hildenbrand , Liu Shixin , Jiri Olsa , Jens Axboe , Alexander Viro Subject: Re: [PATCH v4 2/4] fs/proc/kcore: convert read_kcore() to read_kcore_iter() Message-ID: <070237be-48a2-4a04-bc19-7217b68c8bcf@lucifer.local> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: ADEFDA000B X-Rspam-User: X-Stat-Signature: 87k6itj8cbo487mexajtsqo87neepj1y X-HE-Tag: 1679465977-976906 X-HE-Meta: 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 6Hj3mamA Yhj9ZOA/kg1rzufi2regxYB22NllSDskXV2/IBgfi1XvDtXhndCeqXFmz4rJPRF78kxkkeZn41ziN5SDrEIWFBYm66TaPsRG08Hvz2Vl9pPr9a/jQNmLyV6MCznnqkHmHybkrCNCk5I4RMW1FcSIjsuBbK27PrJAvTqwXTD82SaUvsAMN+OoE9v2mMVki1GmvY+yfbQTxrjvV9sMeObcF6w41x8SfyeZCoMFuqdiGkA5zCL9qh/D9aKPHW6h0EvWYqP8JNAZLP9VFHkXmwtFYGy8K+D/xOUoHxgYqESaShQK6FJO2tmWAcBYMwjVOG3FGCzSngtTAggHLqcd6FS0eLnJzFMuLwDv+31Q57AAafHgtcfBuZgT26SsDwXzLmgp/rsMC7M2+Es5Z0O8= 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 Wed, Mar 22, 2023 at 09:15:48AM +0800, Baoquan He wrote: > Hi Lorenzo, > > On 03/21/23 at 08:54pm, Lorenzo Stoakes wrote: > > Now we have eliminated spinlocks from the vread() case, convert > > read_kcore() to read_kcore_iter(). > > Sorry for late comment. > > Here I could miss something important, I don't get where we have > eliminated spinlocks from the vread() case. Do I misunderstand this > sentence? > Apologies, I didn't update the commit message after the latest revision! We can just drop this sentence altogether. Andrew - could you change the commit message to simply read:- For the time being we still use a bounce buffer for vread(), however in the next patch we will convert this to interact directly with the iterator and eliminate the bounce buffer altogether. Thanks! > > > > For the time being we still use a bounce buffer for vread(), however in the > > next patch we will convert this to interact directly with the iterator and > > eliminate the bounce buffer altogether. > > > > Signed-off-by: Lorenzo Stoakes > > --- > > fs/proc/kcore.c | 58 ++++++++++++++++++++++++------------------------- > > 1 file changed, 29 insertions(+), 29 deletions(-) > > > > diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c > > index 556f310d6aa4..25e0eeb8d498 100644 > > --- a/fs/proc/kcore.c > > +++ b/fs/proc/kcore.c > > @@ -24,7 +24,7 @@ > > #include > > #include > > #include > > -#include > > +#include > > #include > > #include > > #include > > @@ -308,9 +308,12 @@ static void append_kcore_note(char *notes, size_t *i, const char *name, > > } > > > > static ssize_t > > -read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos) > > +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; > > @@ -318,6 +321,7 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos) > > size_t tsz; > > int nphdr; > > unsigned long start; > > + size_t buflen = iov_iter_count(iter); > > size_t orig_buflen = buflen; > > int ret = 0; > > > > @@ -333,7 +337,7 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos) > > notes_offset = phdrs_offset + phdrs_len; > > > > /* ELF file header. */ > > - if (buflen && *fpos < sizeof(struct elfhdr)) { > > + if (buflen && *ppos < sizeof(struct elfhdr)) { > > struct elfhdr ehdr = { > > .e_ident = { > > [EI_MAG0] = ELFMAG0, > > @@ -355,19 +359,18 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos) > > .e_phnum = nphdr, > > }; > > > > - tsz = min_t(size_t, buflen, sizeof(struct elfhdr) - *fpos); > > - if (copy_to_user(buffer, (char *)&ehdr + *fpos, tsz)) { > > + tsz = min_t(size_t, buflen, sizeof(struct elfhdr) - *ppos); > > + if (copy_to_iter((char *)&ehdr + *ppos, tsz, iter) != tsz) { > > ret = -EFAULT; > > goto out; > > } > > > > - buffer += tsz; > > buflen -= tsz; > > - *fpos += tsz; > > + *ppos += tsz; > > } > > > > /* ELF program headers. */ > > - if (buflen && *fpos < phdrs_offset + phdrs_len) { > > + if (buflen && *ppos < phdrs_offset + phdrs_len) { > > struct elf_phdr *phdrs, *phdr; > > > > phdrs = kzalloc(phdrs_len, GFP_KERNEL); > > @@ -397,22 +400,21 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos) > > phdr++; > > } > > > > - tsz = min_t(size_t, buflen, phdrs_offset + phdrs_len - *fpos); > > - if (copy_to_user(buffer, (char *)phdrs + *fpos - phdrs_offset, > > - tsz)) { > > + tsz = min_t(size_t, buflen, phdrs_offset + phdrs_len - *ppos); > > + if (copy_to_iter((char *)phdrs + *ppos - phdrs_offset, tsz, > > + iter) != tsz) { > > kfree(phdrs); > > ret = -EFAULT; > > goto out; > > } > > kfree(phdrs); > > > > - buffer += tsz; > > buflen -= tsz; > > - *fpos += tsz; > > + *ppos += tsz; > > } > > > > /* ELF note segment. */ > > - if (buflen && *fpos < notes_offset + notes_len) { > > + if (buflen && *ppos < notes_offset + notes_len) { > > struct elf_prstatus prstatus = {}; > > struct elf_prpsinfo prpsinfo = { > > .pr_sname = 'R', > > @@ -447,24 +449,23 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos) > > vmcoreinfo_data, > > min(vmcoreinfo_size, notes_len - i)); > > > > - tsz = min_t(size_t, buflen, notes_offset + notes_len - *fpos); > > - if (copy_to_user(buffer, notes + *fpos - notes_offset, tsz)) { > > + tsz = min_t(size_t, buflen, notes_offset + notes_len - *ppos); > > + if (copy_to_iter(notes + *ppos - notes_offset, tsz, iter) != tsz) { > > kfree(notes); > > ret = -EFAULT; > > goto out; > > } > > kfree(notes); > > > > - buffer += tsz; > > buflen -= tsz; > > - *fpos += tsz; > > + *ppos += tsz; > > } > > > > /* > > * Check to see if our file offset matches with any of > > * the addresses in the elf_phdr on our list. > > */ > > - start = kc_offset_to_vaddr(*fpos - data_offset); > > + start = kc_offset_to_vaddr(*ppos - data_offset); > > if ((tsz = (PAGE_SIZE - (start & ~PAGE_MASK))) > buflen) > > tsz = buflen; > > > > @@ -497,7 +498,7 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos) > > } > > > > if (!m) { > > - if (clear_user(buffer, tsz)) { > > + if (iov_iter_zero(tsz, iter) != tsz) { > > ret = -EFAULT; > > goto out; > > } > > @@ -508,14 +509,14 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos) > > case KCORE_VMALLOC: > > vread(buf, (char *)start, tsz); > > /* we have to zero-fill user buffer even if no read */ > > - if (copy_to_user(buffer, buf, tsz)) { > > + if (copy_to_iter(buf, tsz, iter) != tsz) { > > ret = -EFAULT; > > goto out; > > } > > break; > > case KCORE_USER: > > /* User page is handled prior to normal kernel page: */ > > - if (copy_to_user(buffer, (char *)start, tsz)) { > > + if (copy_to_iter((char *)start, tsz, iter) != tsz) { > > ret = -EFAULT; > > goto out; > > } > > @@ -531,7 +532,7 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos) > > */ > > if (!page || PageOffline(page) || > > is_page_hwpoison(page) || !pfn_is_ram(pfn)) { > > - if (clear_user(buffer, tsz)) { > > + if (iov_iter_zero(tsz, iter) != tsz) { > > ret = -EFAULT; > > goto out; > > } > > @@ -541,25 +542,24 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos) > > case KCORE_VMEMMAP: > > case KCORE_TEXT: > > /* > > - * We use _copy_to_user() to bypass usermode hardening > > + * We use _copy_to_iter() to bypass usermode hardening > > * which would otherwise prevent this operation. > > */ > > - if (_copy_to_user(buffer, (char *)start, tsz)) { > > + if (_copy_to_iter((char *)start, tsz, iter) != tsz) { > > ret = -EFAULT; > > goto out; > > } > > break; > > default: > > pr_warn_once("Unhandled KCORE type: %d\n", m->type); > > - if (clear_user(buffer, tsz)) { > > + if (iov_iter_zero(tsz, iter) != tsz) { > > ret = -EFAULT; > > goto out; > > } > > } > > skip: > > buflen -= tsz; > > - *fpos += tsz; > > - buffer += tsz; > > + *ppos += tsz; > > start += tsz; > > tsz = (buflen > PAGE_SIZE ? PAGE_SIZE : buflen); > > } > > @@ -603,7 +603,7 @@ static int release_kcore(struct inode *inode, struct file *file) > > } > > > > static const struct proc_ops kcore_proc_ops = { > > - .proc_read = read_kcore, > > + .proc_read_iter = read_kcore_iter, > > .proc_open = open_kcore, > > .proc_release = release_kcore, > > .proc_lseek = default_llseek, > > -- > > 2.39.2 > > >