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 17:15, <roger.pau@xxxxxxxxxx> wrote:
> On 08/04/14 16:12, Tim Deegan wrote:
>> At 09:30 +0100 on 08 Apr (1396945844), 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.
>>>
>>> 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,
>> 
>> Hmmm.  In that case it seems better; if we're absolutely sure that we
>> can't end up trying to do log-dirty for _migration_ while a guest has
>> a real device passed through, then yes, we can leave them as r/w to
>> the IOMMU. 
>> 
>> Maybe make sure at the same time that full log-dirty mode and
>> needs_iommu are mutually exclusive.
> 
> Would it suffice to add something like:
> 
> case p2m_ram_logdirty:
>     ASSERT(!paging_mode_log_dirty(p2m->domain));

Iirc that would also catch the VRAM dirty tracking, i.e. not be suitable.
I'll defer to Tim though to explain what he had in mind instead.

Jan


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