Re: [Xen-devel] [PATCH 1/2] x86/PoD: prevent guest from being destroyed upon early access to its memory

[Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>]

Am 15.08.2012 15:50, schrieb George Dunlap:
> On Tue, Aug 14, 2012 at 9:45 AM, Jan Beulich<JBeulich@xxxxxxxx>  wrote:
> > x86/PoD: prevent guest from being destroyed upon early access to its memory
> >
> > When an external agent (e.g. a monitoring daemon) happens to access the
> > memory of a PoD guest prior to setting the PoD target, that access must
> > fail for there not being any page in the PoD cache, and only the space
> > above the low 2Mb gets scanned for victim pages (while only the low 2Mb
> > got real pages populated so far).
> >
> > To accomodate for this
> > - set the PoD target first
> > - do all physmap population in PoD mode (i.e. not just large [2Mb or
> >    1Gb] pages)
> > - slightly lift the restrictions enforced by p2m_pod_set_mem_target()
> >    to accomodate for the changed tools behavior
> >
> > Tested-by: Jürgen Groß<juergen.gross@xxxxxxxxxxxxxx>
> >             (in a 4.0.x based incarnation)
> > Signed-off-by: Jan Beulich<jbeulich@xxxxxxxx>
> Acked-by: George Dunlap<george.dunlap@xxxxxxxxxxxxx>
>
> However, my "hg qpush" chokes on the German characters in Juergen's name...
:-)

Feel free to change it to "Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>".


Juergen

>   -George
>
> > --- a/tools/libxc/xc_hvm_build_x86.c
> > +++ b/tools/libxc/xc_hvm_build_x86.c
> > @@ -160,7 +160,7 @@ static int setup_guest(xc_interface *xch
> >       int pod_mode = 0;
> >
> >       if ( nr_pages>  target_pages )
> > -        pod_mode = 1;
> > +        pod_mode = XENMEMF_populate_on_demand;
> >
> >       memset(&elf, 0, sizeof(elf));
> >       if ( elf_init(&elf, image, image_size) != 0 )
> > @@ -197,6 +197,22 @@ static int setup_guest(xc_interface *xch
> >       for ( i = mmio_start>>  PAGE_SHIFT; i<  nr_pages; i++ )
> >           page_array[i] += mmio_size>>  PAGE_SHIFT;
> >
> > +    if ( pod_mode )
> > +    {
> > +        /*
> > +         * Subtract 0x20 from target_pages for the VGA "hole".  Xen will
> > +         * adjust the PoD cache size so that domain tot_pages will be
> > +         * target_pages - 0x20 after this call.
> > +         */
> > +        rc = xc_domain_set_pod_target(xch, dom, target_pages - 0x20,
> > +                                      NULL, NULL, NULL);
> > +        if ( rc != 0 )
> > +        {
> > +            PERROR("Could not set PoD target for HVM guest.\n");
> > +            goto error_out;
> > +        }
> > +    }
> > +
> >       /*
> >        * Allocate memory for HVM guest, skipping VGA hole 0xA0000-0xC0000.
> >        *
> > @@ -208,7 +224,7 @@ static int setup_guest(xc_interface *xch
> >        * ensure that we can be preempted and hence dom0 remains responsive.
> >        */
> >       rc = xc_domain_populate_physmap_exact(
> > -        xch, dom, 0xa0, 0, 0,&page_array[0x00]);
> > +        xch, dom, 0xa0, 0, pod_mode,&page_array[0x00]);
> >       cur_pages = 0xc0;
> >       stat_normal_pages = 0xc0;
> >       while ( (rc == 0)&&  (nr_pages>  cur_pages) )
> > @@ -247,8 +263,7 @@ static int setup_guest(xc_interface *xch
> >                   sp_extents[i] = 
> > page_array[cur_pages+(i<<SUPERPAGE_1GB_SHIFT)];
> >
> >               done = xc_domain_populate_physmap(xch, dom, nr_extents, 
> > SUPERPAGE_1GB_SHIFT,
> > -                                              pod_mode ? 
> > XENMEMF_populate_on_demand : 0,
> > -                                              sp_extents);
> > +                                              pod_mode, sp_extents);
> >
> >               if ( done>  0 )
> >               {
> > @@ -285,8 +300,7 @@ static int setup_guest(xc_interface *xch
> >                       sp_extents[i] = 
> > page_array[cur_pages+(i<<SUPERPAGE_2MB_SHIFT)];
> >
> >                   done = xc_domain_populate_physmap(xch, dom, nr_extents, 
> > SUPERPAGE_2MB_SHIFT,
> > -                                                  pod_mode ? 
> > XENMEMF_populate_on_demand : 0,
> > -                                                  sp_extents);
> > +                                                  pod_mode, sp_extents);
> >
> >                   if ( done>  0 )
> >                   {
> > @@ -302,19 +316,12 @@ static int setup_guest(xc_interface *xch
> >           if ( count != 0 )
> >           {
> >               rc = xc_domain_populate_physmap_exact(
> > -                xch, dom, count, 0, 0,&page_array[cur_pages]);
> > +                xch, dom, count, 0, pod_mode,&page_array[cur_pages]);
> >               cur_pages += count;
> >               stat_normal_pages += count;
> >           }
> >       }
> >
> > -    /* Subtract 0x20 from target_pages for the VGA "hole".  Xen will
> > -     * adjust the PoD cache size so that domain tot_pages will be
> > -     * target_pages - 0x20 after this call. */
> > -    if ( pod_mode )
> > -        rc = xc_domain_set_pod_target(xch, dom, target_pages - 0x20,
> > -                                      NULL, NULL, NULL);
> > -
> >       if ( rc != 0 )
> >       {
> >           PERROR("Could not allocate memory for HVM guest.");
> > --- a/xen/arch/x86/mm/p2m-pod.c
> > +++ b/xen/arch/x86/mm/p2m-pod.c
> > @@ -344,8 +344,9 @@ p2m_pod_set_mem_target(struct domain *d,
> >
> >       pod_lock(p2m);
> >
> > -    /* P == B: Nothing to do. */
> > -    if ( p2m->pod.entry_count == 0 )
> > +    /* P == B: Nothing to do (unless the guest is being created). */
> > +    populated = d->tot_pages - p2m->pod.count;
> > +    if ( populated>  0&&  p2m->pod.entry_count == 0 )
> >           goto out;
> >
> >       /* Don't do anything if the domain is being torn down */
> > @@ -357,13 +358,11 @@ p2m_pod_set_mem_target(struct domain *d,
> >       if ( target<  d->tot_pages )
> >           goto out;
> >
> > -    populated  = d->tot_pages - p2m->pod.count;
> > -
> >       pod_target = target - populated;
> >
> >       /* B<  T': Set the cache size equal to # of outstanding entries,
> >        * let the balloon driver fill in the rest. */
> > -    if ( pod_target>  p2m->pod.entry_count )
> > +    if ( populated>  0&&  pod_target>  p2m->pod.entry_count )
> >           pod_target = p2m->pod.entry_count;
> >
> >       ASSERT( pod_target>= p2m->pod.count );
> >
> >
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxx
> > http://lists.xen.org/xen-devel
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxx
> http://lists.xen.org/xen-devel

--
Juergen Gross                 Principal Developer Operating Systems
PDG ES&S SWE OS6                       Telephone: +49 (0) 89 3222 2967
Fujitsu Technology Solutions              e-mail: juergen.gross@xxxxxxxxxxxxxx
Domagkstr. 28                           Internet: ts.fujitsu.com
D-80807 Muenchen                 Company details: ts.fujitsu.com/imprint.html

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