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From:   "Michael Kelley (LINUX)" <mikelley@microsoft.com>
To:     Wei Liu <wei.liu@kernel.org>,
        Nuno Das Neves <nunodasneves@linux.microsoft.com>
CC:     Tianyu Lan <Tianyu.Lan@microsoft.com>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "iommu@lists.linux.dev" <iommu@lists.linux.dev>,
        Sunil Muthuswamy <sunilmut@microsoft.com>,
        KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Dexuan Cui <decui@microsoft.com>,
        "dwmw2@infradead.org" <dwmw2@infradead.org>,
        "joro@8bytes.org" <joro@8bytes.org>,
        "will@kernel.org" <will@kernel.org>
Subject: RE: [PATCH] iommu/hyper-v: Allow hyperv irq remapping without x2apic
Thread-Topic: [PATCH] iommu/hyper-v: Allow hyperv irq remapping without x2apic
Thread-Index: AQHY9G6MTvL64VjEeUSlJ0XIa/5zY6457YUAgAAElfCAAAq9AIAAB60AgABTl4CABCGJgIAAVIUw
Date:   Mon, 14 Nov 2022 19:09:24 +0000
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From: Wei Liu <wei.liu@kernel.org> Sent: Monday, November 14, 2022 5:59 AM
>=20
> On Fri, Nov 11, 2022 at 02:53:59PM -0800, Nuno Das Neves wrote:
> > On 11/11/2022 9:58 AM, Michael Kelley (LINUX) wrote:
> > > From: Wei Liu <wei.liu@kernel.org> Sent: Friday, November 11, 2022 9:=
27 AM
> [...]
> >
> > I've tested this patch on these Azure SKUs:
> > - Standard_D2S_v2 (intel xapic)
> > - Standard_D4ds_v4 (intel xapic)
> > - Standard_D4ds_v5 (intel x2apic)
> > - Standard_D4ads_v5 (amd xapic)
> >
> > I've tested with linux Dom0 (nested hyperv root partition) and as a
> > regular L1 guest.
> >
>=20
> Okay. I think your tests are good.
>=20
> Michael, do you have any further concern?
>=20

If ms_hyperv_msi_ext_dest_id() returns "true", then
hyperv_prepare_irq_remapping() will still return -ENODEV and you
won't get interrupt remapping because it isn't needed, at least not
for guest VMs.  Is that what we want for the root partition?  Or does
ms_hyperv_msi_ext_dest_id() only return true in a guest partition,
and not in the root partition?  See commit d981059e13ff.

Michael