Re: [PATCH 0/2] Fix issues with untrusted devices and AMD IOMMU

[Christoph Hellwig <hch@infradead.org>]

On Mon, Apr 04, 2022 at 11:47:05AM -0500, Mario Limonciello wrote:
> The bounce buffers were originally set up, but torn down during
> the boot process.
> * This happens because as part of IOMMU initialization
>   `amd_iommu_init_dma_ops` gets called and resets the global swiotlb to 0.
> * When late_init gets called `pci_swiotlb_late_init` `swiotlb_exit` is
>   called and the buffers are torn down.

I think the proper thing is to do this:

diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index a1ada7bff44e6..079694f894b85 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -1838,17 +1838,10 @@ void amd_iommu_domain_update(struct protection_domain *domain)
 	amd_iommu_domain_flush_complete(domain);
 }
 
-static void __init amd_iommu_init_dma_ops(void)
-{
-	swiotlb = (iommu_default_passthrough() || sme_me_mask) ? 1 : 0;
-}
-
 int __init amd_iommu_init_api(void)
 {
 	int err;
 
-	amd_iommu_init_dma_ops();
-
 	err = bus_set_iommu(&pci_bus_type, &amd_iommu_ops);
 	if (err)
 		return err;