From: Dexuan Cui <decui@microsoft.com>
To: Jeffrey Hugo <quic_jhugo@quicinc.com>,
KY Srinivasan <kys@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
Stephen Hemminger <sthemmin@microsoft.com>,
"wei.liu@kernel.org" <wei.liu@kernel.org>,
"lorenzo.pieralisi@arm.com" <lorenzo.pieralisi@arm.com>,
"robh@kernel.org" <robh@kernel.org>,
"kw@linux.com" <kw@linux.com>,
"bhelgaas@google.com" <bhelgaas@google.com>,
Jake Oshins <jakeo@microsoft.com>
Cc: "bjorn.andersson@linaro.org" <bjorn.andersson@linaro.org>,
"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] PCI: hv: Fix multi-MSI to allow more than one MSI vector
Date: Tue, 12 Apr 2022 19:12:42 +0000 [thread overview]
Message-ID: <BYAPR21MB127006D30591602C4BEB6253BFED9@BYAPR21MB1270.namprd21.prod.outlook.com> (raw)
In-Reply-To: <1649772991-10285-1-git-send-email-quic_jhugo@quicinc.com>
> From: Jeffrey Hugo <quic_jhugo@quicinc.com>
> Sent: Tuesday, April 12, 2022 7:17 AM
> ...
> 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@quicinc.com>
Thanks for the fix! This looks good to me.
Reviewed-by: Dexuan Cui <decui@microsoft.com>
next prev parent reply other threads:[~2022-04-12 19:12 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-12 14:16 [PATCH] PCI: hv: Fix multi-MSI to allow more than one MSI vector Jeffrey Hugo
2022-04-12 19:12 ` Dexuan Cui [this message]
2022-04-12 19:32 ` Jeffrey Hugo
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