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Date:   Thu, 7 Jul 2022 20:06:20 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     Alexander Gordeev <agordeev@linux.ibm.com>,
        Alexander Egorenkov <egorenar@linux.ibm.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>, Baoquan He <bhe@redhat.com>,
        Christoph Hellwig <hch@lst.de>, linux-kernel@vger.kernel.org,
        linux-s390@vger.kernel.org
Subject: Re: [PATCH v2 1/1] s390/crash: allow multi-segment iterators
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On Thu, Jul 07, 2022 at 02:31:44PM +0100, Al Viro wrote:
> > @@ -73,10 +73,9 @@ int memcpy_hsa_user(void __user *dest, unsigned long src, size_t count)
> >  		}
> >  		offset = src % PAGE_SIZE;
> >  		bytes = min(PAGE_SIZE - offset, count);
> > -		if (copy_to_user(dest, hsa_buf + offset, bytes))
> > +		if (copy_to_iter(hsa_buf + offset, bytes, iter) != bytes)
> >  			return -EFAULT;
> 
> Umm...  Then you want iov_iter_revert() on short copy...

... maybe better to change the calling convention to return the short
write and have the caller do it if they care?