Re: [Patch v4] x86: irq_comm: Add check for RH bit in kvm_set_msi_irq

[James Sullivan <sullivan.james.f@gmail.com>]

Perfect, thanks for the feedback. I'll get v5 out shortly.

On 03/13/2015 09:08 AM, Radim Krčmář wrote:
> 2015-03-13 08:47-0600, James Sullivan:
>> On 03/13/2015 08:39 AM, Radim Krčmář wrote:
>> ...
>>> The warning message is very clever:
>>> - it contains the magical "may" qualifier and being protected only by
>>>   RH=1 creates weird-looking code structure, but it is technically right
>>>   1) lowest-priority delivery may be set in msi.data, which avoids our
>>>      otherwise incorrect behavior with RH=1/DM=1
>>>   2) RH=1/DM=0 can't deliver to multiple APICs (broadcast is forbidden),
>>>      but real hardware may overwrite delivery mode from msi.data
>>> - being two lines apart adds to suspicion, yet it can be hint to those
>>>   possible problems
>>>
>>> I only fear it is too clever :)
>>>
>>
>> For the error message, how does:
>>
>> 	kvm: MSI RH=1 unsupported, use low-priority delivery mode
>>
>> Sit with you?
> 
> I actually liked the former.
> 
> New one doesn't say what is the impact of the error and the advice is
> not easy follow -- people usually have no idea what low-priority
> delivery mode is and nothing can be done outside of the guest.
> 
> (I put the rant mainly for future reviewers;  the alternative I had in
>  was to warn only when DM=1.)
>