Re: [PATCH v3 2/3] vmcore: Convert __read_vmcore to use an iov_iter

Baoquan He
2021-12-21T06:52:35Z

On 12/13/21 at 02:39pm, Matthew Wilcox (Oracle) wrote:
> This gets rid of copy_to() and let us use proc_read_iter() instead
> of proc_read().
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Acked-by: Baoquan He <bhe@redhat.com>

> ---
> fs/proc/vmcore.c | 81 +++++++++++++++++-------------------------------
> 1 file changed, 29 insertions(+), 52 deletions(-)
>
> diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
> index 958cad6476e6..7b25f568d20d 100644
> --- a/fs/proc/vmcore.c
> +++ b/fs/proc/vmcore.c
> @@ -252,22 +252,8 @@ ssize_t __weak copy_oldmem_page_encrypted(struct iov_iter *iter,
> return copy_oldmem_page(iter, pfn, csize, offset);
> }
>
> -/*
> - * Copy to either kernel or user space
> - */
> -static int copy_to(void *target, void *src, size_t size, int userbuf)
> -{
> - if (userbuf) {
> - if (copy_to_user((char __user *) target, src, size))
> - return -EFAULT;
> - } else {
> - memcpy(target, src, size);
> - }
> - return 0;
> -}
> -
> #ifdef CONFIG_PROC_VMCORE_DEVICE_DUMP
> -static int vmcoredd_copy_dumps(void *dst, u64 start, size_t size, int userbuf)
> +static int vmcoredd_copy_dumps(struct iov_iter *iter, u64 start, size_t size)
> {
> struct vmcoredd_node *dump;
> u64 offset = 0;
> @@ -280,14 +266,13 @@ static int vmcoredd_copy_dumps(void *dst, u64 start, size_t size, int userbuf)
> if (start < offset + dump->size) {
> tsz = min(offset + (u64)dump->size - start, (u64)size);
> buf = dump->buf + start - offset;
> - if (copy_to(dst, buf, tsz, userbuf)) {
> + if (copy_to_iter(buf, tsz, iter) < tsz) {
> ret = -EFAULT;
> goto out_unlock;
> }
>
> size -= tsz;
> start += tsz;
> - dst += tsz;
>
> /* Leave now if buffer filled already */
> if (!size)
> @@ -343,33 +328,28 @@ static int vmcoredd_mmap_dumps(struct vm_area_struct *vma, unsigned long dst,
> /* Read from the ELF header and then the crash dump. On error, negative value is
> * returned otherwise number of bytes read are returned.
> */
> -static ssize_t __read_vmcore(char *buffer, size_t buflen, loff_t *fpos,
> - int userbuf)
> +static ssize_t __read_vmcore(struct iov_iter *iter, loff_t *fpos)
> {
> ssize_t acc = 0, tmp;
> size_t tsz;
> u64 start;
> struct vmcore *m = NULL;
>
> - if (buflen == 0 || *fpos >= vmcore_size)
> + if (iter->count == 0 || *fpos >= vmcore_size)
> return 0;
>
> - /* trim buflen to not go beyond EOF */
> - if (buflen > vmcore_size - *fpos)
> - buflen = vmcore_size - *fpos;
> + iov_iter_truncate(iter, vmcore_size - *fpos);
>
> /* Read ELF core header */
> if (*fpos < elfcorebuf_sz) {
> - tsz = min(elfcorebuf_sz - (size_t)*fpos, buflen);
> - if (copy_to(buffer, elfcorebuf + *fpos, tsz, userbuf))
> + tsz = min(elfcorebuf_sz - (size_t)*fpos, iter->count);
> + if (copy_to_iter(elfcorebuf + *fpos, tsz, iter) < tsz)
> return -EFAULT;
> - buflen -= tsz;
> *fpos += tsz;
> - buffer += tsz;
> acc += tsz;
>
> /* leave now if filled buffer already */
> - if (buflen == 0)
> + if (iter->count == 0)
> return acc;
> }
>
> @@ -390,35 +370,31 @@ static ssize_t __read_vmcore(char *buffer, size_t buflen, loff_t *fpos,
> /* Read device dumps */
> if (*fpos < elfcorebuf_sz + vmcoredd_orig_sz) {
> tsz = min(elfcorebuf_sz + vmcoredd_orig_sz -
> - (size_t)*fpos, buflen);
> + (size_t)*fpos, iter->count);
> start = *fpos - elfcorebuf_sz;
> - if (vmcoredd_copy_dumps(buffer, start, tsz, userbuf))
> + if (vmcoredd_copy_dumps(iter, start, tsz))
> return -EFAULT;
>
> - buflen -= tsz;
> *fpos += tsz;
> - buffer += tsz;
> acc += tsz;
>
> /* leave now if filled buffer already */
> - if (!buflen)
> + if (!iter->count)
> return acc;
> }
> #endif /* CONFIG_PROC_VMCORE_DEVICE_DUMP */
>
> /* Read remaining elf notes */
> - tsz = min(elfcorebuf_sz + elfnotes_sz - (size_t)*fpos, buflen);
> + tsz = min(elfcorebuf_sz + elfnotes_sz - (size_t)*fpos, iter->count);
> kaddr = elfnotes_buf + *fpos - elfcorebuf_sz - vmcoredd_orig_sz;
> - if (copy_to(buffer, kaddr, tsz, userbuf))
> + if (copy_to_iter(kaddr, tsz, iter) < tsz)
> return -EFAULT;
>
> - buflen -= tsz;
> *fpos += tsz;
> - buffer += tsz;
> acc += tsz;
>
> /* leave now if filled buffer already */
> - if (buflen == 0)
> + if (iter->count == 0)
> return acc;
> }
>
> @@ -426,19 +402,17 @@ static ssize_t __read_vmcore(char *buffer, size_t buflen, loff_t *fpos,
> if (*fpos < m->offset + m->size) {
> tsz = (size_t)min_t(unsigned long long,
> m->offset + m->size - *fpos,
> - buflen);
> + iter->count);
> start = m->paddr + *fpos - m->offset;
> - tmp = read_from_oldmem(buffer, tsz, &start,
> - userbuf, cc_platform_has(CC_ATTR_MEM_ENCRYPT));
> + tmp = read_from_oldmem_iter(iter, tsz, &start,
> + cc_platform_has(CC_ATTR_MEM_ENCRYPT));
> if (tmp < 0)
> return tmp;
> - buflen -= tsz;
> *fpos += tsz;
> - buffer += tsz;
> acc += tsz;
>
> /* leave now if filled buffer already */
> - if (buflen == 0)
> + if (iter->count == 0)
> return acc;
> }
> }
> @@ -446,15 +420,14 @@ static ssize_t __read_vmcore(char *buffer, size_t buflen, loff_t *fpos,
> return acc;
> }
>
> -static ssize_t read_vmcore(struct file *file, char __user *buffer,
> - size_t buflen, loff_t *fpos)
> +static ssize_t read_vmcore(struct kiocb *iocb, struct iov_iter *iter)
> {
> - return __read_vmcore((__force char *) buffer, buflen, fpos, 1);
> + return __read_vmcore(iter, &iocb->ki_pos);
> }
>
> /*
> * The vmcore fault handler uses the page cache and fills data using the
> - * standard __vmcore_read() function.
> + * standard __read_vmcore() function.
> *
> * On s390 the fault handler is used for memory regions that can't be mapped
> * directly with remap_pfn_range().
> @@ -464,9 +437,10 @@ static vm_fault_t mmap_vmcore_fault(struct vm_fault *vmf)
> #ifdef CONFIG_S390
> struct address_space *mapping = vmf->vma->vm_file->f_mapping;
> pgoff_t index = vmf->pgoff;
> + struct iov_iter iter;
> + struct kvec kvec;
> struct page *page;
> loff_t offset;
> - char *buf;
> int rc;
>
> page = find_or_create_page(mapping, index, GFP_KERNEL);
> @@ -474,8 +448,11 @@ static vm_fault_t mmap_vmcore_fault(struct vm_fault *vmf)
> return VM_FAULT_OOM;
> if (!PageUptodate(page)) {
> offset = (loff_t) index << PAGE_SHIFT;
> - buf = __va((page_to_pfn(page) << PAGE_SHIFT));
> - rc = __read_vmcore(buf, PAGE_SIZE, &offset, 0);
> + kvec.iov_base = page_address(page);
> + kvec.iov_len = PAGE_SIZE;
> + iov_iter_kvec(&iter, READ, &kvec, 1, PAGE_SIZE);
> +
> + rc = __read_vmcore(&iter, &offset);
> if (rc < 0) {
> unlock_page(page);
> put_page(page);
> @@ -725,7 +702,7 @@ static int mmap_vmcore(struct file *file, struct vm_area_struct *vma)
>
> static const struct proc_ops vmcore_proc_ops = {
> .proc_open = open_vmcore,
> - .proc_read = read_vmcore,
> + .proc_read_iter = read_vmcore,
> .proc_lseek = default_llseek,
> .proc_mmap = mmap_vmcore,
> };
> --
> 2.33.0
>