This is a note to let you know that I've just added the patch titled
PCI: hv: Fix multi-MSI to allow more than one MSI vector
to the 5.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
pci-hv-fix-multi-msi-to-allow-more-than-one-msi-vect.patch
and it can be found in the queue-5.18 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 2729c65017327b32a169f274cf804a9dfe5d5240
Author: Jeffrey Hugo <quic_jhugo@xxxxxxxxxxx>
Date: Wed Apr 13 07:36:21 2022 -0600
PCI: hv: Fix multi-MSI to allow more than one MSI vector
[ Upstream commit 08e61e861a0e47e5e1a3fb78406afd6b0cea6b6d ]
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@xxxxxxxxxxx>
Reviewed-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/1649856981-14649-1-git-send-email-quic_jhugo@xxxxxxxxxxx
Signed-off-by: Wei Liu <wei.liu@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
index d270a204324e..1cbe24b92a38 100644
--- a/drivers/pci/controller/pci-hyperv.c
+++ b/drivers/pci/controller/pci-hyperv.c
@@ -614,7 +614,16 @@ static void hv_set_msi_entry_from_desc(union hv_msi_entry *msi_entry,
static int hv_msi_prepare(struct irq_domain *domain, struct device *dev,
int nvec, msi_alloc_info_t *info)
{
- return pci_msi_prepare(domain, dev, nvec, 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_PCI_MSI)
+ info->flags &= ~X86_IRQ_ALLOC_CONTIGUOUS_VECTORS;
+
+ return ret;
}
/**
