linux-kernel - RE: [PATCH] iommu/hyper-v: Allow hyperv irq remapping without x2apic

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Message-ID: <BYAPR21MB1688FA95BE87E9D1B607B050D7059@BYAPR21MB1688.namprd21.prod.outlook.com>
Date:   Mon, 14 Nov 2022 19:09:24 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Wei Liu <wei.liu@...nel.org>,
        Nuno Das Neves <nunodasneves@...ux.microsoft.com>
CC:     Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        Sunil Muthuswamy <sunilmut@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Dexuan Cui <decui@...rosoft.com>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "joro@...tes.org" <joro@...tes.org>,
        "will@...nel.org" <will@...nel.org>
Subject: RE: [PATCH] iommu/hyper-v: Allow hyperv irq remapping without x2apic

From: Wei Liu <wei.liu@...nel.org> Sent: Monday, November 14, 2022 5:59 AM
> 
> 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@...nel.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.
> >
> 
> Okay. I think your tests are good.
> 
> Michael, do you have any further concern?
> 

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