[Xen-devel] [PATCH resend] vt-d: Fix IM bit mask and unmask of Fault Event Control Register.

[Quan Xu <quan.xu@xxxxxxxxx>]

Bit 0:29 in Fault Event Control Register are 'Reserved and Preserved',
software cannot write 0 to it unconditionally. Software must preserve
the value read for writes.

Signed-off-by: Quan Xu <quan.xu@xxxxxxxxx>
Acked-by: Yang Zhang <yang.z.zhang@xxxxxxxxx>
---
 xen/drivers/passthrough/vtd/iommu.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/xen/drivers/passthrough/vtd/iommu.c 
b/xen/drivers/passthrough/vtd/iommu.c
index 3d98fea..f31d41b 100644
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -992,10 +992,13 @@ static void dma_msi_unmask(struct irq_desc *desc)
 {
     struct iommu *iommu = desc->action->dev_id;
     unsigned long flags;
+    u32 sts;
 
     /* unmask it */
     spin_lock_irqsave(&iommu->register_lock, flags);
-    dmar_writel(iommu->reg, DMAR_FECTL_REG, 0);
+    sts = dmar_readl(iommu->reg, DMAR_FECTL_REG);
+    sts &= ~DMA_FECTL_IM;
+    dmar_writel(iommu->reg, DMAR_FECTL_REG, sts);
     spin_unlock_irqrestore(&iommu->register_lock, flags);
     iommu->msi.msi_attrib.host_masked = 0;
 }
@@ -1004,10 +1007,13 @@ static void dma_msi_mask(struct irq_desc *desc)
 {
     unsigned long flags;
     struct iommu *iommu = desc->action->dev_id;
+    u32 sts;
 
     /* mask it */
     spin_lock_irqsave(&iommu->register_lock, flags);
-    dmar_writel(iommu->reg, DMAR_FECTL_REG, DMA_FECTL_IM);
+    sts = dmar_readl(iommu->reg, DMAR_FECTL_REG);
+    sts |= DMA_FECTL_IM;
+    dmar_writel(iommu->reg, DMAR_FECTL_REG, sts);
     spin_unlock_irqrestore(&iommu->register_lock, flags);
     iommu->msi.msi_attrib.host_masked = 1;
 }
-- 
1.8.3.2


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