Re: [Xen-devel] [PATCH 1/3] xen: drop in_atomic()

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.05.19 at 12:19, <jgross@xxxxxxxx> wrote:
> On 22/05/2019 12:10, Jan Beulich wrote:
>>>>> On 22.05.19 at 11:45, <jgross@xxxxxxxx> wrote:
>>> --- a/xen/arch/x86/hvm/hvm.c
>>> +++ b/xen/arch/x86/hvm/hvm.c
>>> @@ -3185,22 +3185,6 @@ static enum hvm_translation_result __hvm_copy(
>>>  
>>>      ASSERT(is_hvm_vcpu(v));
>>>  
>>> -    /*
>>> -     * XXX Disable for 4.1.0: PV-on-HVM drivers will do grant-table ops
>>> -     * such as query_size. Grant-table code currently does 
> copy_to/from_guest
>>> -     * accesses under the big per-domain lock, which this test would 
> disallow.
>>> -     * The test is not needed until we implement sleeping-on-waitqueue when
>>> -     * we access a paged-out frame, and that's post 4.1.0 now.
>>> -     */
>>> -#if 0
>>> -    /*
>>> -     * If the required guest memory is paged out, this function may sleep.
>>> -     * Hence we bail immediately if called from atomic context.
>>> -     */
>>> -    if ( in_atomic() )
>>> -        return HVMTRANS_unhandleable;
>>> -#endif
>> 
>> Dealing with this TODO item is of course much appreciated, but
>> should it really be deleted altogether? The big-domain-lock issue
>> is gone afair, in which case dropping the #if 0 would seem
>> possible to me, even if it's not strictly needed without the sleep-
>> on-waitqueue behavior mentioned.
> 
> Question is whether it is worth to keep it resulting in the need to
> keep preempt_count() as well.

Well, personally I think keeping it is a small price to pay. But seeing
Andrew's R-b he clearly thinks different. And just to be clear - I
don't really want to veto this change, as at the same time it's also
easy enough to put back if need be. But I'd like this to be give a
2nd consideration at least.

Jan



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