Re: [Xen-devel] [PATCH] x86/PCI: Intercept Dom0 MMCFG from dom0s in HVM containers

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.12.15 at 20:34, <boris.ostrovsky@xxxxxxxxxx> wrote:
> On 12/16/2015 04:04 AM, Jan Beulich wrote:
>>
>>> --- a/xen/arch/x86/hvm/hvm.c
>>> +++ b/xen/arch/x86/hvm/hvm.c
>>> @@ -3116,6 +3116,21 @@ int hvm_hap_nested_page_fault(paddr_t gpa, unsigned 
>>> long gla,
>>>           goto out_put_gfn;
>>>       }
>>>   
>>> +    if ( (p2mt == p2m_mmio_direct) && is_hardware_domain(currd) )
>> The PV condition includes a PFEC_page_present check, and I think
>> an equivalent should be added here too.
> 
> Hmm.. So how would I determine that? I can see how this is available in 
> SVM (although it is not reflected in npfec) but in VMX I don't see 
> direct indication of whether the page was present.

That's what bits 3..5 of the exit qualification can be used for. Really
you could leverage the more fine grained reporting by EPT to make
the condition here "bit 1 must be set" (i.e. npfec.write_access) and
"bit 3 must be set" (readable, which implies present) and "bit 4 must
be clear" (and we might even demand bit 5 to be clear too).

Jan


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