Re: [Xen-devel] [PATCH 1/3] iommu: set correct IOMMU entries when iommu_hap_pt_share == 0

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.04.14 at 11:19, <roger.pau@xxxxxxxxxx> wrote:
> On 08/04/14 10:30, Jan Beulich wrote:
>>>>> On 07.04.14 at 18:02, <roger.pau@xxxxxxxxxx> wrote:
>>> If the memory map is not shared between HAP and IOMMU we fails to set
>>> correct IOMMU mappings for memory types different than p2m_ram_rw.
>>>
>>> This patchs adds IOMMU support for the following memory types:
>>> p2m_grant_map_rw, p2m_map_foreign, p2m_ram_ro and p2m_grant_map_ro.
>> 
>> I'm curious about the justification for p2m_map_foreign; the others
>> I agree with.
> 
> Thanks for the review, I didn't see a reason to not allow DMA transfers
> to/from foreign pages, although there's no user of foreign pages that
> use DMA.

They're rather special (tool stack maps of guest pages), and DMAing
into/out of them shouldn't normally be done. I'd clearly suggest
leaving them unmapped for now.

>> I also wonder whether p2m_ram_logdirty shouldn't be treated
>> equally to p2m_ram_rw: It's clearly better to have some video
>> corruption than to kill the guest due to excessive IOMMU faults,
>> should its kernel choose to DMA into the frame buffer. But at the
>> very minimum this needs to be included alongside p2m_ram_ro.
> 
> Ack. I wasn't sure about p2m_ram_logdirty, so I just decided to not
> include it. I will add it to my next revision as a RW zone if that's fine.

Yes please, subject to Tim saying otherwise.

Jan


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