From: Jeffrey Hugo quic_jhugo@quicinc.com
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().
4.14 backport - file location change to host/pci-hyperv.c. adds the hv_msi_prepare wrapper function. X86_IRQ_ALLOC_TYPE_PCI_MSI changed to X86_IRQ_ALLOC_TYPE_MSI (same value).
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 Link: https://lore.kernel.org/r/1649856981-14649-1-git-send-email-quic_jhugo@quici... 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 --- drivers/pci/host/pci-hyperv.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-)
--- a/drivers/pci/host/pci-hyperv.c +++ b/drivers/pci/host/pci-hyperv.c @@ -908,6 +908,21 @@ static void hv_irq_mask(struct irq_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. @@ -1259,7 +1274,7 @@ static irq_hw_number_t hv_msi_domain_ops
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, };