Re: [Xen-devel] [V10 PATCH 12/23] PVH xen: Support privileged op emulation for PVH

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Thu, Aug 8, 2013 at 8:35 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>>> On 08.08.13 at 03:59, Mukesh Rathor <mukesh.rathor@xxxxxxxxxx> wrote:
>> On Wed, 7 Aug 2013 14:49:50 +0100
>> George Dunlap <dunlapg@xxxxxxxxx> wrote:
>>> On Wed, Jul 24, 2013 at 2:59 AM, Mukesh Rathor <mukesh.rathor@xxxxxxxxxx> 
>>> wrote:
>>> > + * We need vcpu because during context switch, going from PV to
>>> > PVH,
>>> > + * in save_segments() current has been updated to next, and no
>>> > longer pointing
>>> > + * to the PV, but the intention is to get selector for the PV.
>>> > Checking
>>> > + * is_pvh_vcpu(current) will yield incorrect results in such a
>>> > case.
>>> > + */
>>> > +#define read_segment_register(vcpu, regs, name)                   \
>>> > +({  u16 __sel;                                                    \
>>> > +    struct cpu_user_regs *_regs = (regs);                         \
>>> > +                                                                  \
>>> > +    if ( is_pvh_vcpu(vcpu) && guest_mode(_regs) )                 \
>>> > +        __sel = pvh_get_selector(vcpu, x86_seg_##name);           \
>>> > +    else                                                          \
>>> > +        asm volatile ( "movw %%" #name ",%0" : "=r" (__sel) );    \
>>>
>>> Is there a reason you discarded the STR() macro here?
>>
>> Suggested by Jan to change it, not sure the reason. Jan do you recall?
>
> I think this is the result of multiple iterations of the patch, where
> intermediately the stringification had disappeared altogether.
> When I requested it to be restored, I used the simpler # operator
> in the outline.
>
> In any event I think STR() should go away altogether (where
> necessary replaced by __stringify()), and was needlessly used
> in the original code here: The intended use is when you need
> the argument macro expanded before stringification, which is
> not the case here.

OK -- I don't have strong opinions on STR, I just wanted to make sure
it wasn't an oversight.  (Might be worth mentioning this in the change
log.)

 -George

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