2022-07-13 23:41:38

by Suthikulpanit, Suravee

Subject: [PATCH v4 8/9] iommu/amd: Do not support IOMMU_DOMAIN_IDENTITY after SNP is enabled

Once SNP is enabled (by executing SNP_INIT command), IOMMU can no longer
support the passthrough domain (i.e. IOMMU_DOMAIN_IDENTITY).

The SNP_INIT command is called early in the boot process, and would fail
if the kernel is configure to default to passthrough mode.

After the system is already booted, users can try to change IOMMU domain
type of a particular IOMMU group. In this case, the IOMMU driver needs to
check the SNP-enable status and return failure when requesting to change
domain type to identity.

Therefore, return failure when trying to allocate identity domain.

Reviewed-by: Robin Murphy <[email protected]>
Signed-off-by: Suravee Suthikulpanit <[email protected]>
---
drivers/iommu/amd/iommu.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index aedeff8af929..59f9607b34bc 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -2068,6 +2068,14 @@ static struct iommu_domain *amd_iommu_domain_alloc(unsigned type)
{
struct protection_domain *domain;

+ /*
+ * Since DTE[Mode]=0 is prohibited on SNP-enabled system,
+ * default to use IOMMU_DOMAIN_DMA[_FQ].
+ */
+ if (WARN_ONCE(amd_iommu_snp_en && (type == IOMMU_DOMAIN_IDENTITY),
+ "Cannot allocate identity domain due to SNP\n"))
+ return NULL;
+
domain = protection_domain_alloc(type);
if (!domain)
return NULL;
--
2.32.0

2022-07-15 09:22:16

by Joerg Roedel

Subject: Re: [PATCH v4 8/9] iommu/amd: Do not support IOMMU_DOMAIN_IDENTITY after SNP is enabled

On Wed, Jul 13, 2022 at 05:56:50PM -0500, Suravee Suthikulpanit wrote:
> + /*
> + * Since DTE[Mode]=0 is prohibited on SNP-enabled system,
> + * default to use IOMMU_DOMAIN_DMA[_FQ].
> + */
> + if (WARN_ONCE(amd_iommu_snp_en && (type == IOMMU_DOMAIN_IDENTITY),
> + "Cannot allocate identity domain due to SNP\n"))

I removed that WARN_ON_ONCE() here, this is really no condition someone
should worry about.

Regards,

Joerg