Re: [PATCH v3 3/3] xen: rework paging_log_dirty_op to work with hvm guests

["Roger Pau Monné" <roger.pau@citrix.com>]

El 06/05/15 a les 14.10, Jan Beulich ha escrit:
>>>> On 06.05.15 at 13:55, <roger.pau@citrix.com> wrote:
>> El 14/04/15 a les 14.14, Jan Beulich ha escrit:
>>>>>> On 10.04.15 at 19:29, <roger.pau@citrix.com> wrote:
>>>> +                    BUG_ON(((pages >> 3) % PAGE_SIZE) + bytes > PAGE_SIZE);
>>>
>>> I don't seem to be able to spot the original for this one. If there
>>> was none, please make this an ASSERT() instead.
>>
>> Yes, there's no previous BUG_ON because this was not a problem in the
>> past, since we could write to any position on dirty_bitmap, but that's
>> not the case any more. Since we only have one page mapped at a time we
>> need to make sure that what we are about to write doesn't cross a page
>> boundary.
>>
>> I understand this is not an ideal solution, but AFAICT there's no easy
>> way to deal with writes that expand over a page boundary.
> 
> I'm afraid I don't really see what you're asking for. Just to clarify -
> I didn't put anything under question, all I asked for was to use
> ASSERT() instead of BUG_ON() here. Yet what you wrote above
> doesn't seem to related to that request.

I don't think an ASSERT is appropriate here, because it means that on
non-debug versions we might write past the end of the mapped page
without noticing.

Roger.