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Re: [Xen-devel] Shared page tables between ETP and IOMMU issue

El 26/02/15 a les 16.57, Jan Beulich ha escrit:
>>>> On 26.02.15 at 16:45, <roger.pau@xxxxxxxxxx> wrote:
>> While testing PVH Dom0 support on a newer Core i3-5010U I've found that 
>> sharing the page tables between EPT and the IOMMUs don't work. Booting 
>> with iommu=no-sharept solves the problem, but I'm unsure what causes 
>> this issue.
> Is FreeBSD fiddling with its own memory map in some way? It's rather
> surprising to see not just an occasional fault, but many of them, and
> with L2 or even L3 entries not present.

No, FreeBSD doesn't touch the physical memory map at all. No ballooning
or anything like that.

> I.e. if it's not the OS
> requesting re-arrangements, I would suppose table setup itself is
> screwed up in some way. In the end - knowing the valid GFN range
> for the guest - you may want to monitor/log how tables get created
> and whether (and if so by whom) later some of the entries get
> zapped.

OK, I will try to take a look. All those faults come from physical
memory ranges that are supposed to be usable, and in fact the CPU seems
to be able to read/write from them without problems, or else the guest
would have crashed much more early. Regarding sharing the page tables
between EPT and the IOMMU, is there some bit that needs to be set in the
ept entry in order to mark a page as available by the IOMMU?


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