[PATCH v3 2/4] iommu: Add capability for pre-boot DMA protection

Robin Murphy
2022-04-05T20:28:52Z

VT-d's dmar_platform_optin() actually represents a combination of
properties fairly well standardised by Microsoft as "Pre-boot DMA
Protection" and "Kernel DMA Protection"[1]. As such, we can provide
interested consumers with an abstracted capability rather than
driver-specific interfaces that won't scale. We name it for the former
aspect since that's what external callers are most likely to be
interested in; the latter is for the IOMMU layer to handle itself.

[1] https://docs.microsoft.com/en-us/windows-hardware/design/device-experiences/oem-kernel-dma-protection

Suggested-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
drivers/iommu/intel/iommu.c | 2 ++
include/linux/iommu.h | 2 ++
2 files changed, 4 insertions(+)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 255304eb3b1f..49d552a96098 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -4550,6 +4550,8 @@ static bool intel_iommu_capable(struct device *dev, enum iommu_cap cap)
return domain_update_iommu_snooping(NULL);
if (cap == IOMMU_CAP_INTR_REMAP)
return irq_remapping_enabled == 1;
+ if (cap == IOMMU_CAP_PRE_BOOT_PROTECTION)
+ return dmar_platform_optin();

return false;
}
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 1fa927e6f1c6..64c02f472f7b 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -107,6 +107,8 @@ enum iommu_cap {
transactions */
IOMMU_CAP_INTR_REMAP, /* IOMMU supports interrupt isolation */
IOMMU_CAP_NOEXEC, /* IOMMU_NOEXEC flag */
+ IOMMU_CAP_PRE_BOOT_PROTECTION, /* Firmware says it used the IOMMU for
+ DMA protection and we should too */
};

/* These are the possible reserved region types */
--
2.28.0.dirty