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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.04.13 at 20:41, <suravee.suthikulpanit@xxxxxxx> wrote:
> The IOMMU interrupt bits in the IOMMU status registers are
> cleared when writing 1.  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.

So looking through the status register accesses, I would assume
that guest_iommu_mmio_write64() is broken too? In that it
clearly doesn't implement the RW1C behavior for the interrupt
and overflow bits?

Further (as indicated above), the overflow bits being RW1C too,
doesn't iommu_reset_log() need a similar fix
(iommu_set_bit(&entry, of_bit) instead of
iommu_clear_bit(&entry, of_bit))?

And, perhaps even more importantly, iommu_interrupt_handler()
also ought to use iommu_set_bit()? Or wait - isn't this touching
the wrong bits altogether? Logically I would expect interrupt
enable bits to be cleared here, i.e. IOMMU_CONTROL_* to be
used throughout this function instead of IOMMU_STATUS_*.

Jan


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