TXT: Intel IOMMU PMR Disable

(re-posted with apologies for formatting and email addresses)

Disable Intel VT-d (IOMMU) Protected Memory Regions (PMRs) when DMA remapping is enabled.

Leaving the PMRs enabled may add more delay to the VT-d DMA request processing (as another lookup may be performed) but whether they are even used is not deterministic:
DMA requests that are subject to address remapping, and accessing the
protected memory regions may or may not be blocked by hardware. For
such requests, software must not depend on hardware protection of the
protected memory regions, and instead program the DMA-remapping
page-tables to block DMA to protected memory regions.
-- from the description field of the PMEN_REG register in the v1.2
(May '08) VT-d spec.

---

diff -r 29cfdc52a076 drivers/pci/intel-iommu.c
@@ -742,6 +742,22 @@ static void iommu_disable_protect_mem_re

	spin_unlock_irqrestore(&iommu->register_lock, flags);
}

+static void disable_pmr(struct intel_iommu *iommu) +{
+ u32 data;
+
+ data = readl(iommu->reg + DMAR_PMEN_REG);
+ if (!(data & DMA_PMEN_PRS))
+ return;
+
+ data = data & ~DMA_PMEN_EPM;
+ writel(data, iommu->reg + DMAR_PMEN_REG);
+
+ IOMMU_WAIT_OP(iommu, DMAR_PMEN_REG,
+ readl, !(data & DMA_PMEN_PRS), data);
+ return;
+}
+
static int iommu_enable_translation(struct intel_iommu *iommu)

{
	u32 sts;
@@ -755,6 +771,7 @@ static int iommu_enable_translation(stru
		readl, (sts & DMA_GSTS_TES), sts);

	iommu->gcmd |= DMA_GCMD_TE;
+	disable_pmr(iommu);
	spin_unlock_irqrestore(&iommu->register_lock, flags);
	return 0;
}

diff -r 29cfdc52a076 drivers/pci/intel-iommu.h
@@ -158,6 +158,10 @@ static inline void dmar_writeq(void __io

#define DMA_GSTS_FLS (((u32)1) << 29)
#define DMA_GSTS_AFLS (((u32)1) << 28)
#define DMA_GSTS_WBFS (((u32)1) << 27)
+
+/* PMEN_REG */
+#define DMA_PMEN_EPM (((u32)1) << 31)
+#define DMA_PMEN_PRS (((u32)1) << 0)

/* CCMD_REG */
#define DMA_CCMD_ICC (((u64)1) << 63)