RE: [PATCH v5 15/16] x86/hyperv: implement an MSI domain for root partition

[Michael Kelley]

From: Wei Liu <wei.liu@xxxxxxxxxx> Sent: Tuesday, February 2, 2021 9:32 AM
> 
> On Wed, Jan 27, 2021 at 05:47:04AM +0000, Michael Kelley wrote:
> > From: Wei Liu <wei.liu@xxxxxxxxxx> Sent: Wednesday, January 20, 2021 4:01 AM
> > >
> > > When Linux runs as the root partition on Microsoft Hypervisor, its
> > > interrupts are remapped.  Linux will need to explicitly map and unmap
> > > interrupts for hardware.
> > >
> > > Implement an MSI domain to issue the correct hypercalls. And initialize
> > > this irqdomain as the default MSI irq domain.
> > >
> > > Signed-off-by: Sunil Muthuswamy <sunilmut@xxxxxxxxxxxxx>
> > > Co-Developed-by: Sunil Muthuswamy <sunilmut@xxxxxxxxxxxxx>
> > > Signed-off-by: Wei Liu <wei.liu@xxxxxxxxxx>
> > > ---
> > > v4: Fix compilation issue when CONFIG_PCI_MSI is not set.
> > > v3: build irqdomain.o for 32bit as well.
> >
> > I'm not clear on the intent for 32-bit builds.  Given that hv_proc.c is built
> > only for 64-bit, I'm assuming running Linux in the root partition
> > is only functional for 64-bit builds.  So is the goal simply that 32-bit
> > builds will compile correctly?  Seems like maybe there should be
> > a CONFIG option for running Linux in the root partition, and that
> > option would force 64-bit.
> 
> To ensure 32 bit kernel builds and 32 bit guests still work.
> 
> The config option ROOT_API is to be introduced by Nuno's /dev/mshv
> series. We can use that option to gate some objects when that's
> available.
> 

But just so I'm 100% clear, is there intent to run 32-bit Linux in the root
partition?  I'm assuming not.

Michael