From: Wei Liu <wei.liu@kernel.org>
To: Jeffrey Hugo <quic_jhugo@quicinc.com>
Cc: kys@microsoft.com, haiyangz@microsoft.com,
sthemmin@microsoft.com, wei.liu@kernel.org, decui@microsoft.com,
lorenzo.pieralisi@arm.com, robh@kernel.org, kw@linux.com,
bhelgaas@google.com, jakeo@microsoft.com,
bjorn.andersson@linaro.org, linux-hyperv@vger.kernel.org,
linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] PCI: hv: Fix multi-MSI to allow more than one MSI vector
Date: Mon, 25 Apr 2022 15:33:44 +0000 [thread overview]
Message-ID: <20220425153344.lgo3kdnrbef75jcq@liuwe-devbox-debian-v2> (raw)
In-Reply-To: <2100eed4-8081-6070-beaf-7c6ba65ad9be@quicinc.com>
On Wed, Apr 20, 2022 at 08:13:22AM -0600, Jeffrey Hugo wrote:
> 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@quicinc.com>
> > Reviewed-by: Dexuan Cui <decui@microsoft.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.
I expect the PCI maintainers to pick this up. If I don't see this picked
up in this week I will apply it to hyperv-next.
Thanks,
Wei.
>
> Thanks
>
> -Jeff
next prev parent reply other threads:[~2022-04-25 15:33 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-13 13:36 [PATCH v2] PCI: hv: Fix multi-MSI to allow more than one MSI vector Jeffrey Hugo
2022-04-20 14:13 ` Jeffrey Hugo
2022-04-25 15:33 ` Wei Liu [this message]
2022-04-25 15:49 ` Wei Liu
2022-04-25 16:52 ` Jeffrey Hugo
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