[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH for 4.6] x86/mm: make {set, clear}_identity_p2m_mapping() work for HVM guests as well



>>> On 14.09.15 at 16:24, <andrew.cooper3@xxxxxxxxxx> wrote:
> For Intel IGD passthrough, the guest driver programs the device to DMA
> to/from its RMRR.
> 
> c/s 619ecf8 "make {set,clear}_identity_p2m_mapping() work for PV guests"
> was incomplete for pre-Broadwell systems which did not support shared
> EPT.
> 
> The correct check to use is iommu_use_hap_pt() not
> paging_mode_translate() as IOMMU mappings also need to be created for
> HVM guests with separate EPT and IOMMU tables.

No, at least not without a very good explanation:

> --- a/xen/arch/x86/mm/p2m.c
> +++ b/xen/arch/x86/mm/p2m.c
> @@ -957,7 +957,7 @@ int set_identity_p2m_entry(struct domain *d, unsigned 
> long gfn,
>      struct p2m_domain *p2m = p2m_get_hostp2m(d);
>      int ret;
>  
> -    if ( !paging_mode_translate(p2m->domain) )
> +    if ( !iommu_use_hap_pt(d) )

Not only have these checks no reason to be in any way IOMMU
dependent (no other function around here does so), but also
both ept_set_entry() and p2m_pt_set_entry() take care to call
iommu_{,un}map_page() as needed (as I had already pointed
out back when we discussed the patch this one tries to complete).
If anything, it would be those low level functions that may need
tweaking (and which have a reason to consider IOMMU flags) if
for some reason they don't actually do the expected calls.

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel


 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.