The justification for dropping p2m_mmio_dm from p2m_is_valid() was wrong
for two of the shadow mode uses.
In _sh_propagate() we want to create special L1 entries for p2m_mmio_dm
pages. Hence we need to make sure we don't bail early for that type.
In _sh_page_fault() we want to handle p2m_mmio_dm by forwarding to
(internal or external) emulation. Pull the !p2m_is_mmio() check out of
the || expression (as otherwise it would need adding to the lhs as
well).
In both cases, p2m_is_valid() in combination with p2m_is_grant() still
doesn't cover foreign mappings. Hence use p2m_is_any_ram() plus (as
necessary) p2m_mmio_* instead.
Fixes: be59cceb2dbb ("x86/P2M: don't include MMIO_DM in p2m_is_valid()")
Reported-by: Luca Fancellu <luca.fance...@arm.com>
Signed-off-by: Jan Beulich <jbeul...@suse.com>
---
This still leaves the p2m_mmio_dm vs p2m_invalid unaddressed.
While propagating #PF to the guest based on P2M type isn't quite right,
not doing so in sh_page_fault() would lead to no forward progress in the
guest anymore: If we put in place a non-present shadow PTE, another #PF
will occur right after exiting to the guest. Doing so is only okay as a
transient measure, e.g. while paging back in a paged-out page (where the
respective type is included in P2M_RAM_TYPES).
There could likely be at least one more Fixes: tag (to cover the lack of
handling foreign mappings); the one supplied is merely to indicate the
connection to the recent regression.
--- a/xen/arch/x86/mm/shadow/multi.c
+++ b/xen/arch/x86/mm/shadow/multi.c
@@ -471,9 +471,7 @@ _sh_propagate(struct vcpu *v,
/* We don't shadow PAE l3s */
ASSERT(GUEST_PAGING_LEVELS > 3 || level != 3);
- /* Check there's something for the shadows to map to */
- if ( (!p2m_is_valid(p2mt) && !p2m_is_grant(p2mt))
- || !gfn_valid(d, target_gfn) )
+ if ( !gfn_valid(d, target_gfn) )
{
*sp = shadow_l1e_empty();
goto done;
@@ -503,6 +501,13 @@ _sh_propagate(struct vcpu *v,
goto done;
}
+ /* Check there's something for the shadows to map to */
+ if ( !p2m_is_any_ram(p2mt) && p2mt != p2m_mmio_direct )
+ {
+ *sp = shadow_l1e_empty();
+ goto done;
+ }
+
// Must have a valid target_mfn unless this is a prefetch or an l1
// pointing at MMIO space. In the case of a prefetch, an invalid
// mfn means that we can not usefully shadow anything, and so we
@@ -2366,8 +2371,8 @@ static int cf_check sh_page_fault(
gmfn = get_gfn(d, gfn, &p2mt);
if ( shadow_mode_refcounts(d) &&
- ((!p2m_is_valid(p2mt) && !p2m_is_grant(p2mt)) ||
- (!p2m_is_mmio(p2mt) && !mfn_valid(gmfn))) )
+ !p2m_is_mmio(p2mt) &&
+ (!p2m_is_any_ram(p2mt) || !mfn_valid(gmfn)) )
{
perfc_incr(shadow_fault_bail_bad_gfn);
SHADOW_PRINTK("BAD gfn=%"SH_PRI_gfn" gmfn=%"PRI_mfn"\n",
