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From:   Michael Kelley <mikelley@microsoft.com>
To:     Wei Liu <wei.liu@kernel.org>
CC:     Linux on Hyper-V List <linux-hyperv@vger.kernel.org>,
        "virtualization@lists.linux-foundation.org" 
        <virtualization@lists.linux-foundation.org>,
        Linux Kernel List <linux-kernel@vger.kernel.org>,
        Vineeth Pillai <viremana@linux.microsoft.com>,
        Sunil Muthuswamy <sunilmut@microsoft.com>,
        Nuno Das Neves <nunodasneves@linux.microsoft.com>,
        "pasha.tatashin@soleen.com" <pasha.tatashin@soleen.com>,
        KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>
Subject: RE: [PATCH v5 15/16] x86/hyperv: implement an MSI domain for root
 partition
Thread-Topic: [PATCH v5 15/16] x86/hyperv: implement an MSI domain for root
 partition
Thread-Index: AQHW7yP6HaVdmem27E2jxVVgXGHGnKo6+DxggAo8E4CAAAsYcA==
Date:   Tue, 2 Feb 2021 18:15:23 +0000
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From: Wei Liu <wei.liu@kernel.org> Sent: Tuesday, February 2, 2021 9:32 AM
>=20
> On Wed, Jan 27, 2021 at 05:47:04AM +0000, Michael Kelley wrote:
> > From: Wei Liu <wei.liu@kernel.org> 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 initiali=
ze
> > > this irqdomain as the default MSI irq domain.
> > >
> > > Signed-off-by: Sunil Muthuswamy <sunilmut@microsoft.com>
> > > Co-Developed-by: Sunil Muthuswamy <sunilmut@microsoft.com>
> > > 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-bi=
t
> > 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.
>=20
> To ensure 32 bit kernel builds and 32 bit guests still work.
>=20
> 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.
>=20

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

Michael