Re: [Xen-devel] [PATCH RFC V4 4/5] xen, libxc: Request page fault injection via libxc

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 08/04/2014 06:22 PM, Razvan Cojocaru wrote:
> On 08/04/2014 06:21 PM, Jan Beulich wrote:
>>>>> On 04.08.14 at 17:11, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>>> On 08/04/2014 05:26 PM, Jan Beulich wrote:
>>>>>>> On 04.08.14 at 13:30, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>>>>> +static bool_t vmx_check_pf_injection(void)
>>>>> +{
>>>>> +    struct vcpu *curr = current;
>>>>> +    struct domain *d = curr->domain;
>>>>> +    struct segment_register seg;
>>>>> +    unsigned long ev;
>>>>> +    uint32_t pending_event = 0;
>>>>> +
>>>>> +    if ( likely(d->arch.hvm_domain.fault_info.virtual_address == 0 )
>>>>
>>>> Bad space before ). And my question stands: Why is VA zero
>>>> special?
>>>
>>> It's special because for our purposes (mostly Windows HVM guests, but I
>>> think the same applies to Linux), that page is reserved and it's never
>>> swapped out, so there would be no point in asking for a page fault
>>> injection there.
>>>
>>> If you think that a code comment is not enough here and that in the
>>> future somebody might legitimately want to use 0 as a proper value, I'll
>>> add a "valid" member and use that explicitly.
>>
>> Perhaps in another thread I said this earlier today already: In the
>> HVM code we should not be making assumptions about particular
>> guest behavior, except when it comes to optimization for certain
>> special cases.
> 

OK, I'll address that as well.


Thanks,
Razvan Cojocaru

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