Re: [RFC PATCH 01/14] fs/proc/vmcore: Update read_from_oldmem() for user pointer

[Amit Kachhap]

On 12/6/21 7:34 PM, Christoph Hellwig wrote:
> On Fri, Dec 03, 2021 at 04:12:18PM +0530, Amit Daniel Kachhap wrote:
> > +	return read_from_oldmem_to_kernel(buf, count, ppos,
> > +					  cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT));
>
> Overly long line.
>
> > +ssize_t read_from_oldmem(char __user *ubuf, char *kbuf, size_t count,
> > +			 u64 *ppos, bool encrypted)
> >   {
> >   	unsigned long pfn, offset;
> >   	size_t nr_bytes;
> > @@ -156,19 +163,27 @@ ssize_t read_from_oldmem(char *buf, size_t count,
> >   		/* If pfn is not ram, return zeros for sparse dump files */
> >   		if (!pfn_is_ram(pfn)) {
> >   			tmp = 0;
> > -			if (!userbuf)
> > -				memset(buf, 0, nr_bytes);
> > -			else if (clear_user(buf, nr_bytes))
> > +			if (kbuf)
> > +				memset(kbuf, 0, nr_bytes);
> > +			else if (clear_user(ubuf, nr_bytes))
> >   				tmp = -EFAULT;
>
> This looks like a huge mess.  What speak against using an iov_iter
> here?

iov_iter seems to be a reasonable way. As a start I thought of adding
minimal changes.

>