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    Subject[PATCH 2/2] vfio/type1: Give hardware MSI regions precedence
    Date
    If the IOMMU driver advertises 'real' reserved regions for MSIs, but
    still includes the software-managed region as well, we are currently
    blind to the former and will configure the IOMMU domain to map MSIs into
    the latter, which is unlikely to work as expected.

    Since it would take a ridiculous hardware topology for both regions to
    be valid (which would be rather difficult to support in general), we
    should be safe to assume that the presence of any hardware regions makes
    the software region irrelevant. However, the IOMMU driver might still
    advertise the software region by default, particularly if the hardware
    regions are filled in elsewhere by generic code, so it might not be fair
    for VFIO to be super-strict about not mixing them. To that end, make
    vfio_iommu_has_sw_msi() robust against the presence of both region types
    at once, so that we end up doing what is almost certainly right, rather
    than what is almost certainly wrong.

    Signed-off-by: Robin Murphy <robin.murphy@arm.com>
    ---
    drivers/vfio/vfio_iommu_type1.c | 12 ++++++++++--
    1 file changed, 10 insertions(+), 2 deletions(-)

    diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
    index 2328be628f21..92155cce926d 100644
    --- a/drivers/vfio/vfio_iommu_type1.c
    +++ b/drivers/vfio/vfio_iommu_type1.c
    @@ -1169,13 +1169,21 @@ static bool vfio_iommu_has_sw_msi(struct iommu_group *group, phys_addr_t *base)
    INIT_LIST_HEAD(&group_resv_regions);
    iommu_get_group_resv_regions(group, &group_resv_regions);
    list_for_each_entry(region, &group_resv_regions, list) {
    + /*
    + * The presence of any 'real' MSI regions should take
    + * precedence over the software-managed one if the
    + * IOMMU driver happens to advertise both types.
    + */
    + if (region->type == IOMMU_RESV_MSI) {
    + ret = false;
    + break;
    + }
    +
    if (region->type == IOMMU_RESV_SW_MSI) {
    *base = region->start;
    ret = true;
    - goto out;
    }
    }
    -out:
    list_for_each_entry_safe(region, next, &group_resv_regions, list)
    kfree(region);
    return ret;
    --
    2.12.2.dirty
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