Re: [Xen-devel] [PATCH 3/4] move XENMEM_add_to_physmap_range handling framework to common code

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.12.13 at 16:59, Tim Deegan <tim@xxxxxxx> wrote:
> At 14:35 +0000 on 18 Dec (1387373737), Jan Beulich wrote:
>> There's really nothing really architecture specific here; the
>> architecture specific handling is limited to
>> xenmem_add_to_physmap_one().
>> 
>> Note the restriction of XENMAPSPACE_gmfn_range only being supported
>> through XENMEM_add_to_physmap is being dropped as being pointless.
> 
> Hmmm.   With that restriction removed, this: 
> 
>> +        rc = xenmem_add_to_physmap_one(d, xatpr->space,
>> +                                       xatpr->foreign_domid,
>> +                                       idx, gpfn);
>> +
>> +        if ( unlikely(__copy_to_guest_offset(xatpr->errs, 0, &rc, 1)) )
>> +        {
>> +            rc = -EFAULT;
>> +            goto out;
>> +        }
>> +
>> +        guest_handle_add_offset(xatpr->idxs, 1);
>> +        guest_handle_add_offset(xatpr->gpfns, 1);
>> +        guest_handle_add_offset(xatpr->errs, 1);
>> +        xatpr->size--;
>> +
>> +        /* Check for continuation if it's not the last interation. */
>> +        if ( xatpr->size > 0 && hypercall_preempt_check() )
>> +        {
>> +            rc = -EAGAIN;
>> +            goto out;
>> +        }
> 
> will save the partial result of a preempted XENMAPSPACE_gmfn_range
> sub-op into the errors array, and then the whole operation may or may
> not return -EAGAIN.
> 
> I guess the caller now has enough information to figure out what
> happened and restart, but given that the rest of this interface nicely
> hides preemption from the caller, it's a bit of an ugly corner case.

I'm afraid I don't follow: XENMAPSPACE_gmfn_range and
XENMAPSPACE_gmfn will be treated equally now - there simply
is no range being specified for the individual
add_to_physmap_range elements. After all,
xenmem_add_to_physmap_one() - as its name says - really only
processes a single page.

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel