[RFC][PATCH 2/3] TXT: Intel IOMMU PMR Disable

[Joseph Cihula]

(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.

Signed-off-by:  Shane Wang <shane.wang@xxxxxxxxx>
Signed-off-by:  Joseph Cihula <joseph.cihula@xxxxxxxxx>

---

diff -r 29cfdc52a076 drivers/pci/intel-iommu.c
--- a/drivers/pci/intel-iommu.c	Mon Oct 06 12:50:47 2008 -0700
+++ b/drivers/pci/intel-iommu.c	Mon Oct 06 15:54:59 2008 -0700
@@ -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
--- a/drivers/pci/intel-iommu.h	Mon Oct 06 12:50:47 2008 -0700
+++ b/drivers/pci/intel-iommu.h	Mon Oct 06 15:54:59 2008 -0700
@@ -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)


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