Re: [PATCH v3 4/8] s390/airq: use DMA memory for adapter interrupts

[Cornelia Huck <cohuck@redhat.com>]

On Tue, 4 Jun 2019 15:22:56 +0200
Halil Pasic <pasic@linux.ibm.com> wrote:

> On Mon, 3 Jun 2019 17:27:40 +0200
> Cornelia Huck <cohuck@redhat.com> wrote:

> > Apologies if that already has been answered (and I missed it in my mail
> > pile...), but two things had come to my mind previously:
> > 
> > - CHSC... does anything need to be done there? Last time I asked:
> >   "Anyway, css_bus_init() uses some chscs
> >    early (before cio_dma_pool_init), so we could not use the pools
> >    there, even if we wanted to. Do chsc commands either work, or else
> >    fail benignly on a protected virt guest?"  
> 
> Protected virt won't support all CHSC. The supported ones won't requre
> use of shared memory. So we are fine.

I suppose the supported ones are the sync chscs that use the chsc area
as a direct parameter (and therefore are handled similarly to the other
I/O instructions that supply a direct parameter)? I don't think we care
about async chscs in KVM/QEMU anyway, as we don't even emulate chsc
subchannels :) (And IIRC, you don't get chsc subchannels in z/VM
guests, either.)

> 
> > - PCI indicators... does this interact with any dma configuration on
> >   the pci device? (I know pci is not supported yet, and I don't really
> >   expect any problems.)
> >   
> 
> It does but, I'm pretty confident we don't have a problem with PCI. IMHO
> Sebastian is the guy who needs to be paranoid about this, and he r-b-ed
> the respective patches.

Just wanted to make sure that this was on the radar. You guys are
obviously in a better position than me to judge this :)

Anyway, I do not intend to annoy with those questions, it's just hard
to get a feel if there are areas that still need care if you don't have
access to the documentation for this... if you tell me that you are
aware of it and it should work, that's fine for me.