Commit d6e41a92 authored Jul 25, 2022 by Jeffrey Hugo Committed by Greg Kroah-Hartman Jul 29, 2022

PCI: hv: Fix multi-MSI to allow more than one MSI vector



commit 08e61e861a0e47e5e1a3fb78406afd6b0cea6b6d upstream.

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().

4.19 backport - adds the hv_msi_prepare wrapper function.
X86_IRQ_ALLOC_TYPE_PCI_MSI changed to X86_IRQ_ALLOC_TYPE_MSI
(same value).

Fixes: 4daace0d ("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>
Link: https://lore.kernel.org/r/1649856981-14649-1-git-send-email-quic_jhugo@quicinc.com


Signed-off-by: Wei Liu <wei.liu@kernel.org>
Signed-off-by: Carl Vanderlip <quic_carlv@quicinc.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent c46cc629

drivers/pci/controller/pci-hyperv.c

+16 −1

Original line number	Diff line number	Diff line
		@@ -893,6 +893,21 @@ static void hv_irq_mask(struct irq_data *data)
		pci_msi_mask_irq(data);
		}

		static int hv_msi_prepare(struct irq_domain domain, struct device dev,
		int nvec, msi_alloc_info_t *info)
		{
		int ret = pci_msi_prepare(domain, dev, nvec, info);

		/*
		* By using the interrupt remapper in the hypervisor IOMMU, contiguous
		* CPU vectors is not needed for multi-MSI
		*/
		if (info->type == X86_IRQ_ALLOC_TYPE_MSI)
		info->flags &= ~X86_IRQ_ALLOC_CONTIGUOUS_VECTORS;

		return ret;
		}

		/**
		* hv_irq_unmask() - "Unmask" the IRQ by setting its current
		* affinity.
		@@ -1240,7 +1255,7 @@ static irq_hw_number_t hv_msi_domain_ops_get_hwirq(struct msi_domain_info *info,

		static struct msi_domain_ops hv_msi_ops = {
		.get_hwirq = hv_msi_domain_ops_get_hwirq,
		.msi_prepare = pci_msi_prepare,
		.msi_prepare = hv_msi_prepare,
		.set_desc = pci_msi_set_desc,
		.msi_free = hv_msi_free,
		};