Re: ARM fixes for my improved privcmd patch.

[Mats Petersson <mats.petersson@citrix.com>]

On 19/12/12 15:45, Ian Campbell wrote:
> On Wed, 2012-12-19 at 15:08 +0000, Mats Petersson wrote:
>> On 19/12/12 12:22, Ian Campbell wrote:
>>> On Wed, 2012-12-19 at 12:10 +0000, Mats Petersson wrote:
>>>
>>>>>> +                  only likely to return EFAULT or some other "things are very
>>>>>> +                  bad" error code, which the rest of the calling code won't
>>>>>> +                  be able to fix up. So we just exit with the error we got.
>>>>> It expect it is more important to accumulate the individual errors from
>>>>> remap_pte_fn into err_ptr.
>>>> Yes, but since that exits on error with EFAULT, the calling code won't
>>>> "accept" the errors, and thus the whole house of cards fall apart at
>>>> this point.
>>>>
>>>> There should probably be a task to fix this up properly, hence the
>>>> comment. But right now, any error besides ENOENT is "unacceptable" by
>>>> the callers of this code. If you want me to add this to the comment, I'm
>>>> happy to. But as long as remap_pte_fn returns EFAULT on error, nothing
>>>> will work after an error.
>>> Are you sure? privcmd.c has some special casing for ENOENT but it looks
>>> like it should just pass through other errors back to userspace.
>>>
>>> In any case surely this needs fixing?
>>>
>>> On the X86 side err_ptr is the result of the mmupdate hypercall which
>>> can already be other than ENOENT, including EFAULT, ESRCH etc.
>> Yes, but the ONLY error that is "acceptable" (as in, doesn't lead to the
>> calling code revoking the mapping and returning an error) is ENOENT.
> Hr, Probably the right thing is for map_foreign_page to propagate the
> result of XENMEM_add_to_physmap_range and for remap_pte_fn to store it
> in err_ptr. That -EFAULT thing just looks wrong to me.
Ok, so you want me to fix that up, I suppose? I mean, I just copied the 
behaviour that was already there - just massaged the code around a bit...

--
Mats
>
>> Or at least, that's how I believe it should SHOULD be - since only
>> ENOENT is a "success" error code, anything else pretty much means that
>> the operation requested didn't work properly. If you are aware of any
>> use-case where EFAULT, ESRCH or other error codes would still result in
>> a valid, usable memory mapping - I have a fair understanding of the xc_*
>> code, and although I may not know every piece of that code, I'm fairly
>> certainly that is the expected behaviour.
>>
>> --
>> Mats
>>> Ian.
>>>
>