Re: [PATCH v3 2/4] libxc: support of linear p2m list for migration of pv-domains

[Wei Liu <wei.liu2@citrix.com>]

On Thu, Jan 07, 2016 at 11:21:04AM +0100, Juergen Gross wrote:
> On 06/01/16 16:40, Wei Liu wrote:
> > On Wed, Dec 16, 2015 at 10:24:18AM +0100, Juergen Gross wrote:
> > [...]
> >> @@ -698,21 +868,19 @@ static int normalise_pagetable(struct xc_sr_context *ctx, const uint64_t *src,
> >>              /* 32bit guests can only use the first 4 entries of their L3 tables.
> >>               * All other are potentially used by Xen. */
> >>              xen_first = 4;
> >> -            xen_last = 512;
> >> +            xen_last = 511;
> > 
> > Is this a bug fix in its own right?
> 
> Hmm, bug fix is too much. It is a harmonization with the change below
> using macros to set xen_last to 511 at maximum. In fact it doesn't
> matter, because xen_last is used in:
> 
>    if ( i >= xen_first && i <= xen_last )
> 
> with i being in the range from 0 to 511.
> 

Yes, that's what I was thinking. There seemed to be an off-by-one error
in the code. But as you said, i is within [0,511] so the code is fine.

Could you add a words or two about this hunk in commit message please.

With that:

Reviewed-by: Wei Liu <wei.liu2@citrix.com>

Wei.

> 
> Juergen
> 
> > 
> > Wei.
> > 
> >>              break;
> >>  
> >>          case XEN_DOMCTL_PFINFO_L2TAB:
> >>              /* It is hard to spot Xen mappings in a 32bit guest's L2.  Most
> >>               * are normal but only a few will have Xen mappings.
> >> -             *
> >> -             * 428 = (HYPERVISOR_VIRT_START_PAE >> L2_PAGETABLE_SHIFT_PAE)&0x1ff
> >> -             *
> >> -             * ...which is conveniently unavailable to us in a 64bit build.
> >>               */
> >> -            if ( pte_to_frame(src[428]) == ctx->x86_pv.compat_m2p_mfn0 )
> >> +            i = (HYPERVISOR_VIRT_START_X86_32 >> L2_PAGETABLE_SHIFT_PAE) & 511;
> >> +            if ( pte_to_frame(src[i]) == ctx->x86_pv.compat_m2p_mfn0 )
> >>              {
> >> -                xen_first = 428;
> >> -                xen_last = 512;
> >> +                xen_first = i;
> >> +                xen_last = (HYPERVISOR_VIRT_END_X86_32 >>
> >> +                            L2_PAGETABLE_SHIFT_PAE) & 511;
> >>              }
> >>              break;
> >>          }
> >> -- 
> >> 2.6.2
> >>
> > 
> > _______________________________________________
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> > Xen-devel@lists.xen.org
> > http://lists.xen.org/xen-devel
> > 
>