Re: [Xen-ia64-devel] [Patch] Fix for re-enabling PV-on-HVM on IPF

[Doi.Tsunehisa@xxxxxxxxxxxxxx]

Hi Yamahata-san,

  Thank you for your comment.

You (yamahata) said:
> On Thu, Mar 08, 2007 at 01:06:04PM +0900, DOI Tsunehisa wrote:
> > diff -r 61eb6589e720 -r b602dd142385 xen/arch/ia64/xen/mm.c
> > --- a/xen/arch/ia64/xen/mm.c        Tue Mar 06 21:11:37 2007 +0900
> > +++ b/xen/arch/ia64/xen/mm.c        Thu Mar 08 11:57:46 2007 +0900
> > @@ -2110,12 +2125,31 @@ arch_memory_op(int op, XEN_GUEST_HANDLE(
> >  
> >          /* Unmap from old location, if any. */
> >          gpfn = get_gpfn_from_mfn(mfn);
> > -        if (gpfn != INVALID_M2P_ENTRY)
> > +        if (gpfn != INVALID_M2P_ENTRY) {
> > +            unsigned long x, nx;
> > +            /*
> > +             * guest_physmap_remove_page() (for IPF) descrements page
> > +             * counter and unset PGC_allocated flag,
> > +             * so pre-increment page counter and post-set flag inserte
d
> > +             */
> > +            /* pre-increment page counter */
> > +            get_page(mfn_to_page(mfn), d);
> 
> Please check the return value.

  I agree. I'll modify it.

>> +
>>              guest_physmap_remove_page(d, gpfn, mfn);
>> +
>> +            /* post-set PGC_allocated flag */
>> +            do {
>> +                x = mfn_to_page(mfn)->count_info;
>> +                if ((x & PGC_count_mask) == 0)
>> +                    goto out;
>> +                nx = x | PGC_allocated;
>> +            } while (cmpxchg_acq(&mfn_to_page(mfn)->count_info, x, nx)
>>  != x);
>> +        }
> 
> checking == 0 is non-sense because we incremented it.
> Probably you want to 
>    if (!test_and_set_bit(page->count_info, _PGC_allocated)) {
>       put_page(page);
>       goto out;
>    }

  guest_physmap_remove_page() unsets PGC_allocated flag, thus
this test_and_set_bit() returns zero allways, I think.

  In this code, I assumed that hypervisor might be destructing the
domain. In this case, the page counter might be zero.

Thanks,
- Tsunehisa Doi

_______________________________________________
Xen-ia64-devel mailing list
Xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-ia64-devel