On Thu, 2007-11-01 at 11:34 +0000, Tim Deegan wrote:
> At 11:18 +0000 on 01 Nov (1193915902), Kieran Mansley wrote:
> > I'm a bit concerned about this one in _sh_propogate(). It seems it's
> > checking that the mfn is valid for a good reason, and so letting it
> > carry on in the case of MMIO frames will lead to a rather ungraceful
> > failure. If I modify the above if to be:
> >
> > if ( !mfn_valid(target_mfn) && (p2mt != p2m_mmio_direct)
> > && !iomem_access_permitted(d, target_mfn, target_mfn))
> >
> > so that PV iomem frames can continue rather than giving up at this
> > point, it gets a fatal page fault (see below).
>
> Oh dear. Yes, you'll need to protect all the stuff further down that
> tries to mark the frame dirty. Probably making sh_mfn_is_dirty test for
> !mfn_valid(mfn) and return 0 will be enough.
See attached patch.
I opted instead to surround the section that calls sh_mfn_is_dirty()
with
if ( mfn_valid(target_mfn) ||
!iomem_access_permitted(d, target_mfn, target_mfn) )
because if sh_mfn_is_dirty() returned zero on a bad mfn, it would remove
the _PAGE_RW flag.
I'm not 100% sure this patch is complete or correct or doesn't have side
effects, but it works for me. I'd appreciate it if you could give it a
once over to make sure it makes sense. If it does, and isn't too big a
risk for 3.2.0, applying it to that would be great.
One question in my mind is whether the tests of iomem_access_permitted()
in _sh_propogate() would be better replaced with the more general
shadow_mode_translate(). The former seemed less risky to me as
otherwise any invalid mfn could drop through when !shadow_mode_translate
(), and this test was originally designed to filter them out.
Signed-off-by Kieran Mansley <kmansley@xxxxxxxxxxxxxx>
Thanks
Kieran
fix iomem frame shadow propogation to allow live migration
diff -r b28fa67d3940 xen/arch/x86/mm/shadow/multi.c
--- a/xen/arch/x86/mm/shadow/multi.c Thu Nov 01 11:52:34 2007 +0000
+++ b/xen/arch/x86/mm/shadow/multi.c Thu Nov 01 16:02:36 2007 +0000
@@ -28,6 +28,7 @@
#include <xen/sched.h>
#include <xen/perfc.h>
#include <xen/domain_page.h>
+#include <xen/iocap.h>
#include <asm/page.h>
#include <asm/current.h>
#include <asm/shadow.h>
@@ -696,7 +697,8 @@ _sh_propagate(struct vcpu *v,
/* N.B. For pass-through MMIO, either this test needs to be
relaxed,
* and shadow_set_l1e() trained to handle non-valid MFNs (ugh), or
the
* MMIO areas need to be added to the frame-table to make them
"valid". */
- if ( !mfn_valid(target_mfn) && (p2mt != p2m_mmio_direct) )
+ if ( !mfn_valid(target_mfn) && (p2mt != p2m_mmio_direct) &&
+ !iomem_access_permitted(d, target_mfn, target_mfn) )
{
ASSERT((ft == ft_prefetch));
*sp = shadow_l1e_empty();
@@ -709,9 +711,12 @@ _sh_propagate(struct vcpu *v,
// SHADOW_PRESENT bit.
//
pass_thru_flags = (_PAGE_DIRTY | _PAGE_ACCESSED | _PAGE_USER |
- _PAGE_RW | _PAGE_PRESENT);
+ _PAGE_RW | _PAGE_PRESENT );
if ( guest_supports_nx(v) )
pass_thru_flags |= _PAGE_NX_BIT;
+ if ( !mfn_valid(target_mfn) &&
+ iomem_access_permitted(d, target_mfn, target_mfn) )
+ pass_thru_flags |= _PAGE_PCD | _PAGE_PWT;
sflags = gflags & pass_thru_flags;
/* Only change memory caching type for pass-through domain */
@@ -758,10 +763,13 @@ _sh_propagate(struct vcpu *v,
// p2m_ram_logdirty p2m type: only HAP uses that.)
if ( unlikely((level == 1) && shadow_mode_log_dirty(d)) )
{
- if ( ft & FETCH_TYPE_WRITE )
- paging_mark_dirty(d, mfn_x(target_mfn));
- else if ( !sh_mfn_is_dirty(d, target_mfn) )
- sflags &= ~_PAGE_RW;
+ if ( mfn_valid(target_mfn) ||
+ !iomem_access_permitted(d, target_mfn, target_mfn) ) {
+ if ( ft & FETCH_TYPE_WRITE )
+ paging_mark_dirty(d, mfn_x(target_mfn));
+ else if ( !sh_mfn_is_dirty(d, target_mfn) )
+ sflags &= ~_PAGE_RW;
+ }
}
/* Read-only memory */
@@ -2836,7 +2844,8 @@ static int sh_page_fault(struct vcpu *v,
gfn = guest_l1e_get_gfn(gw.eff_l1e);
gmfn = gfn_to_mfn(d, gfn, &p2mt);
- if ( !p2m_is_valid(p2mt) || (!p2m_is_mmio(p2mt) && !mfn_valid
(gmfn)) )
+ if ( !shadow_mode_translate(d) &&
+ (!p2m_is_valid(p2mt) || (!p2m_is_mmio(p2mt) && !mfn_valid
(gmfn))) )
{
perfc_incr(shadow_fault_bail_bad_gfn);
SHADOW_PRINTK("BAD gfn=%"SH_PRI_gfn" gmfn=%"PRI_mfn"\n",
iomem_shadow
Description: Text document
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