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

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

El 26/02/15 a les 19.02, Roger Pau Monné ha escrit:
> El 26/02/15 a les 17.43, Jan Beulich ha escrit:
>>>>> On 26.02.15 at 17:29, <roger.pau@xxxxxxxxxx> wrote:
>>> 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?
>>
>> Bits 0 and 1 (read and write) are shared between VT-d and EPT
>> (as is bit 7 - see struct dma_pte and ept_entry_t).
> 
> I've added some debug prints at the end of construct_dom0 to print the 
> MFN of a RAM page (using get_gfn_query_unlocked) and the VTd entry 
> (using print_vtd_entries):
> 
> (XEN) print_vtd_entries: iommu ffff8302197c3a40 dev 0000:00:1f.2 gmfn 43e0
> (XEN)     root_entry = ffff8302197c0000
> (XEN)     root_entry[0] = 140144001
> (XEN)     context = ffff830140144000
> (XEN)     context[fa] = 2_140148001
> (XEN)     l4 = ffff830140148000
> (XEN)     l4_index = 0
> (XEN)     l4[0] = 140147003
> (XEN)     l3 = ffff830140147000
> (XEN)     l3_index = 0
> (XEN)     l3[0] = 140146003
> (XEN)     l2 = ffff830140146000
> (XEN)     l2_index = 21
> (XEN)     l2[21] = 0
> (XEN)     l2[21] not present
> (XEN) GFN: 0x43e0 MFN: 0x1401e3 type: 0
> 
> This is before Dom0 has been started, so I think there's something 
> wrong in the way we build the page tables, because AFAICT the VTd 
> code is not able to resolve the GFN, but the EPT code is.

BTW, if I set no-sharept the output is as expected:

(XEN) print_vtd_entries: iommu ffff8302197c3a40 dev 0000:00:1f.2 gmfn 43e0
(XEN)     root_entry = ffff8302197c0000
(XEN)     root_entry[0] = 19793f001
(XEN)     context = ffff83019793f000
(XEN)     context[fa] = 2_140149001
(XEN)     l4 = ffff830140149000
(XEN)     l4_index = 0
(XEN)     l4[0] = 140148003
(XEN)     l3 = ffff830140148000
(XEN)     l3_index = 0
(XEN)     l3[0] = 140147003
(XEN)     l2 = ffff830140147000
(XEN)     l2_index = 21
(XEN)     l2[21] = 14012c003
(XEN)     l1 = ffff83014012c000
(XEN)     l1_index = 1e0
(XEN)     l1[1e0] = 1401e3003
(XEN) GFN: 0x43e0 MFN: 0x1401e3 type: 0


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