On 5/16/2025 8:13 PM, Philippe Mathieu-Daudé wrote:
On 16/5/25 12:05, Sairaj Kodilkar wrote:
Commit c1f46999ef506 ("amd_iommu: Add support for pass though mode")
introduces the support for "pt" flag by enabling nodma memory when
"pt=off". This allowed VFIO devices to successfully register notifiers
by using nodma region.
But, This also broke things when guest is booted with the iommu=nopt
because, devices bypass the IOMMU and use untranslated addresses
(IOVA) to
perform DMA reads/writes to the nodma memory region, ultimately
resulting in
a failure to setup the devices in the guest.
Fix the above issue by always enabling the amdvi_dev_as->iommu memory
region.
But this will once again cause VFIO devices to fail while registering the
notifiers with AMD IOMMU memory region.
Fixes: c1f46999ef506 ("amd_iommu: Add support for pass though mode")
Signed-off-by: Sairaj Kodilkar <sarun...@amd.com>
Reviewed-by: Vasant Hegde <vasant.he...@amd.com>
---
hw/i386/amd_iommu.c | 12 ++----------
1 file changed, 2 insertions(+), 10 deletions(-)
diff --git a/hw/i386/amd_iommu.c b/hw/i386/amd_iommu.c
index 5f9b95279997..df8ba5d39ada 100644
--- a/hw/i386/amd_iommu.c
+++ b/hw/i386/amd_iommu.c
@@ -1426,7 +1426,6 @@ static AddressSpace *amdvi_host_dma_iommu(PCIBus
*bus, void *opaque, int devfn)
AMDVIState *s = opaque;
AMDVIAddressSpace **iommu_as, *amdvi_dev_as;
int bus_num = pci_bus_num(bus);
- X86IOMMUState *x86_iommu = X86_IOMMU_DEVICE(s);
iommu_as = s->address_spaces[bus_num];
@@ -1486,15 +1485,8 @@ static AddressSpace
*amdvi_host_dma_iommu(PCIBus *bus, void *opaque, int devfn)
AMDVI_INT_ADDR_FIRST,
&amdvi_dev_as->iommu_ir,
1);
- if (!x86_iommu->pt_supported) {
- memory_region_set_enabled(&amdvi_dev_as->iommu_nodma,
false);
- memory_region_set_enabled(MEMORY_REGION(&amdvi_dev_as-
>iommu),
- true);
- } else {
- memory_region_set_enabled(MEMORY_REGION(&amdvi_dev_as-
>iommu),
- false);
- memory_region_set_enabled(&amdvi_dev_as->iommu_nodma, true);
- }
+ memory_region_set_enabled(&amdvi_dev_as->iommu_nodma, false);
I have no clue about this device but wonder what is the usefulness of
iommu_nodma now, isn't it dead code?
Hi Philippe,
Indeed the iommu_nodma is dead. The reason I did not remove the
iommu_nodma region completely is that, Alejandro's DMA remapping patches
[1] uses this region to dynamically switch the address space.
[1]
https://lore.kernel.org/qemu-devel/20250502021605.1795985-1-alejandro.j.jime...@oracle.com/
Thanks
Sairaj
+ memory_region_set_enabled(MEMORY_REGION(&amdvi_dev_as-
>iommu), true);
}
return &iommu_as[devfn]->as;
}
