Re: [Xen-devel] [PATCH 1/2 v3] iommu/amd: Fix logic for clearing the IOMMU interrupt bits

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 10.06.13 at 12:56, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
> The IOMMU interrupt bits in the IOMMU status registers are
> "read-only, and write-1-to-clear (RW1C).  Therefore, the existing
> logic which reads the register, set the bit, and then writing back
> the values could accidentally clear certain bits if it has been set.
> 
> The correct logic would just be writing only the value which only
> set the interrupt bits, and leave the rest to zeros.
> 
> This patch also, clean up #define masks as Jan has suggested.
> 
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
> 
> With iommu_interrupt_handler() properly having got switched its readl()
> from status to control register, the subsequent writel() needed to be
> switched too (and the RW1C comment there was bogus).
> 
> Further, with iommu_interrupt_handler() now actually disabling the
> interrupt sources, they also need to get re-enabled by the tasklet once
> it finished processing the respective log.

Finally, guest write emulation to the status register needs to be done
with the RW1C (and RO for all other bits) semantics in mind too.

> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan


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