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SubjectRe: [PATCH] NOMMU: use copy_*_user_page() in access_process_vm()
On 12/08/2009 06:57 PM, David Howells wrote:
> Mike Frysinger<vapier@gentoo.org> wrote:
>
>> + copy_to_user_page(vma, NULL, NULL,
>> + (void *) addr, buf, len);
>> ...
>> + copy_from_user_page(vma, NULL, NULL,
>> + buf, (void *) addr, len);
>
> I think this is not correct. The third parameter in both cases (vaddr) is of
> unsigned long type (so should be 0 not NULL), and should not be left zero in
> any case. I think it should be passed addr. In fact, we should really pass
> the second parameter too (page), though for now, I'm happy to leave that NULL.
>
> See attached revision of the patch.
>
I agree on using 0 instead of NULL. But for !MMU, I think, vaddr is
always as same as addr. So we don't need to pass it?


Jie


> David
> ---
> From: Jie Zhang<jie.zhang@analog.com>
> Subject: [PATCH] NOMMU: Use copy_*_user_page() in access_process_vm()
>
> The MMU code uses the copy_*_user_page() variants in access_process_vm()
> rather than copy_*_user() as the former includes an icache flush. This is
> important when doing things like setting software breakpoints with gdb.
> So switch the NOMMU code over to do the same.
>
> This patch makes the reasonable assumption that copy_from_user_page() won't
> fail - which is probably fine, as we've checked the VMA from which we're
> copying is usable, and the copy is not allowed to cross VMAs. The one case
> where it might go wrong is if the VMA is a device rather than RAM, and that
> device returns an error which - in which case rubbish will be returned rather
> than EIO.
>
> Signed-off-by: Jie Zhang<jie.zhang@analog.com>
> Signed-off-by: Mike Frysinger<vapier@gentoo.org>
> Signed-off-by: David Howells<dhowells@redhat.com>
> ---
>
> mm/nommu.c | 6 ++++--
> 1 files changed, 4 insertions(+), 2 deletions(-)
>
>
> diff --git a/mm/nommu.c b/mm/nommu.c
> index af12270..953800f 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -1896,9 +1896,11 @@ int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, in
>
> /* only read or write mappings where it is permitted */
> if (write&& vma->vm_flags& VM_MAYWRITE)
> - len -= copy_to_user((void *) addr, buf, len);
> + copy_to_user_page(vma, NULL, addr,
> + (void *) addr, buf, len);
> else if (!write&& vma->vm_flags& VM_MAYREAD)
> - len -= copy_from_user(buf, (void *) addr, len);
> + copy_from_user_page(vma, NULL, addr,
> + buf, (void *) addr, len);
> else
> len = 0;
> } else {



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