linux-kernel - Re: [PATCH v2] PCI: hv: Fix multi-MSI to allow more than one MSI vector

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Message-ID: <2100eed4-8081-6070-beaf-7c6ba65ad9be@quicinc.com>
Date:   Wed, 20 Apr 2022 08:13:22 -0600
From:   Jeffrey Hugo <quic_jhugo@...cinc.com>
To:     <kys@...rosoft.com>, <haiyangz@...rosoft.com>,
        <sthemmin@...rosoft.com>, <wei.liu@...nel.org>,
        <decui@...rosoft.com>, <lorenzo.pieralisi@....com>,
        <robh@...nel.org>, <kw@...ux.com>, <bhelgaas@...gle.com>,
        <jakeo@...rosoft.com>
CC:     <bjorn.andersson@...aro.org>, <linux-hyperv@...r.kernel.org>,
        <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] PCI: hv: Fix multi-MSI to allow more than one MSI
 vector

On 4/13/2022 7:36 AM, Jeffrey Hugo wrote:
> If the allocation of multiple MSI vectors for multi-MSI fails in the core
> PCI framework, the framework will retry the allocation as a single MSI
> vector, assuming that meets the min_vecs specified by the requesting
> driver.
> 
> Hyper-V advertises that multi-MSI is supported, but reuses the VECTOR
> domain to implement that for x86.  The VECTOR domain does not support
> multi-MSI, so the alloc will always fail and fallback to a single MSI
> allocation.
> 
> In short, Hyper-V advertises a capability it does not implement.
> 
> Hyper-V can support multi-MSI because it coordinates with the hypervisor
> to map the MSIs in the IOMMU's interrupt remapper, which is something the
> VECTOR domain does not have.  Therefore the fix is simple - copy what the
> x86 IOMMU drivers (AMD/Intel-IR) do by removing
> X86_IRQ_ALLOC_CONTIGUOUS_VECTORS after calling the VECTOR domain's
> pci_msi_prepare().
> 
> Fixes: 4daace0d8ce8 ("PCI: hv: Add paravirtual PCI front-end for Microsoft Hyper-V VMs")
> Signed-off-by: Jeffrey Hugo <quic_jhugo@...cinc.com>
> Reviewed-by: Dexuan Cui <decui@...rosoft.com>
> ---

Ping?

I don't see this in -next, nor have I seen any replies.  It is possible 
I have missed some kind of update, but currently I'm wondering if this 
change is progressing or not.  If there is some kind of process used in 
this area, I'm not familiar with it, so I would appreciate an introduction.

Thanks

-Jeff