On 2020-03-12 6:19 pm, Andre Przywara wrote:
When we try to get an MSI cookie for a VFIO device, that can fail if
CONFIG_IOMMU_DMA is not set. In this case iommu_get_msi_cookie() returns
-ENODEV, and that should not be fatal.
Ignore that case and proceed with the initialisation.
This fixes VFIO with a platform device on the Calxeda Midway (no MSIs).
Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
---
Hi,
not sure this is the right fix, or we should rather check if the
platform doesn't support MSIs at all (which doesn't seem to be easy
to do).
Or is this because arm-smmu.c always reserves an IOMMU_RESV_SW_MSI
region?
Both, really - ideally VFIO should be able to skip all MSI_related setup
if the system doesn't support MSIs, but equally the SMMU drivers would
also ideally not expose a pointless SW_MSI region in the same situation.
In lieu of a 'nice' way of acheiving that, I think this patch seems
reasonable - ENODEV doesn't clash with any real error that can occur
when iommu-dma is present, and carrying on without a cookie should be
fine since the MSI hooks that would otherwise dereference it will also
be no-ops.
Perhaps it might be worth a comment to clarify that this is specifically
to allow vfio-platform to work with iommu-dma disabled, but either way,
Acked-by: Robin Murphy <robin.murphy@xxxxxxx>
Also this seems to be long broken, actually since Eric introduced MSI
support in 4.10-rc3, but at least since the initialisation order was
fixed with f6810c15cf9.
I'm sure the entire Midway userbase have been up-in-arms the whole
time... :P
Robin.
Grateful for any insight.
Cheers,
Andre
drivers/vfio/vfio_iommu_type1.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index a177bf2c6683..467e217ef09a 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -1786,7 +1786,7 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
if (resv_msi) {
ret = iommu_get_msi_cookie(domain->domain, resv_msi_base);
- if (ret)
+ if (ret && ret != -ENODEV)
goto out_detach;
}
