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

["Radim Krčmář" <rkrcmar@redhat.com>]

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.)