Re: [Xen-devel] PCI Pass-through in Xen ARM: Draft 4

[Manish Jaggi <mjaggi@xxxxxxxxxxxxxxxxxx>]

On Tuesday 01 September 2015 01:02 PM, Jan Beulich wrote:
> > > > On 31.08.15 at 14:36, <mjaggi@xxxxxxxxxxxxxxxxxx> wrote:
> > On Thursday 13 August 2015 03:12 PM, Manish Jaggi wrote:
> > >   4.2.1 Mapping BAR regions in guest address space
> > >   -----------------------------------------------------------------------------
> > >
> > >   When a PCI-EP device is assigned to a domU the toolstack will read
> > > the pci
> > >   configuration space BAR registers. Toolstack allocates a virtual BAR
> > >   region for each BAR region, from the area reserved in guest address
> > > space for
> > >   mapping BARs referred to as Guest BAR area. This area is defined in
> > >   public/arch-arm.h
> > >
> > >   /* For 32bit BARs*/
> > >   #define GUEST_BAR_BASE_32 <<>>
> > >   #define GUEST_BAR_SIZE_32 <<>>
> > >
> > >   /* For 64bit BARs*/
> > >   #define GUEST_BAR_BASE_64 <<>>
> > >   #define GUEST_BAR_SIZE_64 <<>>
> > >
> > >   Toolstack then invokes domctl xc_domain_memory_mapping to map in stage2
> > >   translation. If a BAR region address is 32b BASE_32 area would be used,
> > >   otherwise 64b. If a combination of both is required the support is TODO.
> > >
> > >   Toolstack manages these areas and allocate from these area. The
> > > allocation
> > >   and deallocation is done using APIs similar to malloc and free.
> > To implement this feature in xl tools there is required to have a malloc
> > and free from the reserved area.
> > Can we have the XEN_DOMCTL_memory_mapping extended with a flag say
> > ALLOCATE/FREE_FROM_BAR_AREA.
> > When this flag is passed xen would add or remove the stage2 mapping for
> > the domain.
> > This will make use of the code already present in xen.
> Above it was said that the tool stack manages this area (including
> allocations from it). Why would this require a new hypercall?
As a rule xl tools should manage the guest memory map. Now if it does by 
itself or initiates it is another thing.
Allocating an area for PCI BAR and freeing it reserved area  would 
require adding  allocator code in xl tools.
Since xen already knows about the area (as it is defined in public 
header file) and there exists code in xen,
i believe it make sense to use that rather than adding the same in xl tools.


> Jan
>
>
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