Messages in this thread Patch in this message | | | From | Robin Murphy <> | Subject | [PATCH] iommu: Fix def_domain_type interaction with untrusted devices | Date | Tue, 16 Apr 2024 14:00:43 +0100 |
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Previously, an untrusted device forcing IOMMU_DOMAIN_DMA always took precedence over whatever a driver's def_domain_type may have wanted to say. This was intentionally handled in core code since 3 years prior, to avoid drivers poking at the details of what is essentially a policy between the PCI core and the IOMMU core. Now, though, we go to the length of evaluating both constraints to check for any conflict, and if so throw our toys out of the pram and refuse to handle the device at all. Regardless of any intent, in practice this leaves the device, and potentially the rest of its group or even the whole IOMMU, in a largely undetermined state, which at worst may render the whole system unusable. Unfortunately it turns out that this is a realistic situation to run into by connecting a PASID-capable device (e.g. a GPU) to an AMD-based laptop via a Thunderbolt expansion box, since the AMD IOMMU driver needs an identity default domain for PASIDs to be usable, and thus sets a def_domain_type override based on PASID capability.
In general, restoring the old behaviour of forcing translation will not make that device's operation any more broken than leaving it potentially blocked or subject to the rest of a group's translations would, nor will it be any less safe than leaving it potentially bypassed or subject to the rest of a group's translations would, so do that, and let eGPUs work again.
Reported-by: Eric Wagner <ewagner12@gmail.com> Link: https://lore.kernel.org/linux-iommu/CAHudX3zLH6CsRmLE-yb+gRjhh-v4bU5_1jW_xCcxOo_oUUZKYg@mail.gmail.com Fixes: 59ddce4418da ("iommu: Reorganize iommu_get_default_domain_type() to respect def_domain_type()") Signed-off-by: Robin Murphy <robin.murphy@arm.com> --- drivers/iommu/iommu.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c index 996e79dc582d..90dbea14d4d6 100644 --- a/drivers/iommu/iommu.c +++ b/drivers/iommu/iommu.c @@ -1772,9 +1772,8 @@ static int iommu_get_default_domain_type(struct iommu_group *group, if (driver_type && driver_type != IOMMU_DOMAIN_DMA) { dev_err_ratelimited( untrusted, - "Device is not trusted, but driver is overriding group %u to %s, refusing to probe.\n", + "IOMMU_DOMAIN_DMA for untrusted device overrides driver request of %s for group %u, expect issues...\n", group->id, iommu_domain_type_str(driver_type)); - return -1; } driver_type = IOMMU_DOMAIN_DMA; } -- 2.39.2.101.g768bb238c484.dirty
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