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

[Baoquan He <bhe@redhat.com>]

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
>