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    PCI: hv: Fix multi-MSI to allow more than one MSI vector · 08e61e86
    Jeffrey Hugo 提交于
    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: 4daace0d ("PCI: hv: Add paravirtual PCI front-end for Microsoft Hyper-V VMs")
    Signed-off-by: NJeffrey Hugo <quic_jhugo@quicinc.com>
    Reviewed-by: NDexuan Cui <decui@microsoft.com>
    Link: https://lore.kernel.org/r/1649856981-14649-1-git-send-email-quic_jhugo@quicinc.comSigned-off-by: NWei Liu <wei.liu@kernel.org>
    08e61e86
pci-hyperv.c 106.2 KB