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    Subject[PATCH 4.19 59/62] PCI: hv: Fix multi-MSI to allow more than one MSI vector
    Date
    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().

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

    Fixes: 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@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>
    ---
    drivers/pci/controller/pci-hyperv.c | 17 ++++++++++++++++-
    1 file changed, 16 insertions(+), 1 deletion(-)

    --- a/drivers/pci/controller/pci-hyperv.c
    +++ b/drivers/pci/controller/pci-hyperv.c
    @@ -893,6 +893,21 @@ 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.
    @@ -1240,7 +1255,7 @@ 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,
    };

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