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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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?

Jan


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