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

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

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.


Thanks,
Razvan Cojocaru

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