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

From: Wei Liu <wei.liu@kernel.org> Sent: Tuesday, February 2, 2021 9:32 AM

On Wed, Jan 27, 2021 at 05:47:04AM +0000, Michael Kelley wrote:

quoted

From: Wei Liu <wei.liu@kernel.org> Sent: Wednesday, January 20, 2021 4:01 AM

quoted

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 <redacted>
Co-Developed-by: Sunil Muthuswamy <redacted>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
---
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