Re: [RFC PATCH v2 2/5] iommu/virtio-iommu: Add probe request

Hi Jean-Philippe,

On 19/01/18 17:21, Jean-Philippe Brucker wrote:

On 16/01/18 23:26, Auger Eric wrote:
[...]

quoted

quoted

+	switch (mem->subtype) {
+	case VIRTIO_IOMMU_RESV_MEM_T_MSI:
+		region = iommu_alloc_resv_region(addr, size, prot,
+						 IOMMU_RESV_MSI);

if (!region)
	return -ENOMEM;

quoted

+		break;
+	case VIRTIO_IOMMU_RESV_MEM_T_RESERVED:
+	default:
+		region = iommu_alloc_resv_region(addr, size, 0,
+						 IOMMU_RESV_RESERVED);

same.

I'll add them, thanks

quoted

There is another issue related to the exclusion of iovas belonging to
reserved regions. Typically on x86, when attempting to run
virtio-blk-pci with iommu I eventually saw the driver using iova
belonging to the IOAPIC regions to map phys addr and this stalled qemu
with a drown trace:

"virtio: bogus descriptor or out of resources"

those regions need to be excluded from the iova allocator. This was
resolved by adding
if (iommu_dma_init_domain(domain,
			  vdev->viommu->geometry.aperture_start,
			  vdev->viommu->geometry.aperture_end,
			  dev))
in viommu_attach_dev()

The most recent hack for x86 [1] does call iommu_dma_init_domain() in
attach_dev(). Is it buggy?

Oh OK. Actually I have never used that branch and in my version the last
arg of iommu_dma_init_domain was NULL hence the issue. But I was
thinking more generally that care must be taken to exclude all those
regions.

Thanks

Eric

We probably shouldn't call iommu_dma_init_domain() unconditionally
(outside of CONFIG_X86 that is), since it's normally done by the arch
(arch/arm64/mm/dma-mapping.c)

Thanks,
Jean

[1]
http://www.linux-arm.org/git?p=linux-jpb.git;a=commitdiff;h=e910e224b58712151dda06df595a53ff07edef63
on branch virtio-iommu/v0.5-x86