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

["Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>]

Xu, Quan wrote on 2015-09-25:
> Signed-off-by: Quan Xu <quan.xu@xxxxxxxxx>

Though the patch is simple, the necessary description still is required, like:
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.

Other part:

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;
>  }


Best regards,
Yang



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