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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH v2 8/9] x86/pagewalk: Improve the logic behind setting access and dirty bits
The boolean pse2M is misnamed, because it might refer to a 4M superpage.
Switch the logic to be in terms of the level of the leaf entry, and rearrange
the calls to set_ad_bits() to be a fallthrough switch statement, to make it
easier to follow.
Alter set_ad_bits() to use properly use bool rather than integers. Introduce
properly typed pointers rather than repeatedly casting away from void. Use
ACCESS_ONCE() to ensure that *walk_p is only read once.
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Tim Deegan <tim@xxxxxxx>
CC: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
v2:
* New
---
xen/arch/x86/mm/guest_walk.c | 81 +++++++++++++++++++++++++-------------------
1 file changed, 47 insertions(+), 34 deletions(-)
diff --git a/xen/arch/x86/mm/guest_walk.c b/xen/arch/x86/mm/guest_walk.c
index bdb52d9..4ba7602 100644
--- a/xen/arch/x86/mm/guest_walk.c
+++ b/xen/arch/x86/mm/guest_walk.c
@@ -32,24 +32,28 @@ asm(".file \"" __OBJECT_FILE__ "\"");
#include <asm/page.h>
#include <asm/guest_pt.h>
-/* Modify a guest pagetable entry to set the Accessed and Dirty bits.
- * Returns non-zero if it actually writes to guest memory. */
-static uint32_t set_ad_bits(void *guest_p, void *walk_p, int set_dirty)
+/*
+ * Modify a guest pagetable entry to set the Accessed and Dirty bits.
+ * Returns non-zero if it actually writes to guest memory.
+ */
+static bool set_ad_bits(void *_guest_p, void *_walk_p, bool set_dirty)
{
- guest_intpte_t old, new;
+ guest_intpte_t *guest_p = _guest_p, *walk_p = _walk_p;
+ guest_intpte_t new, old = ACCESS_ONCE(*walk_p);
- old = *(guest_intpte_t *)walk_p;
new = old | _PAGE_ACCESSED | (set_dirty ? _PAGE_DIRTY : 0);
- if ( old != new )
+ if ( old != new )
{
- /* Write the new entry into the walk, and try to write it back
+ /*
+ * Write the new entry into the walk, and try to write it back
* into the guest table as well. If the guest table has changed
- * under out feet then leave it alone. */
- *(guest_intpte_t *)walk_p = new;
- if ( cmpxchg(((guest_intpte_t *)guest_p), old, new) == old )
- return 1;
+ * under out feet then leave it alone.
+ */
+ *walk_p = new;
+ if ( cmpxchg(guest_p, old, new) == old )
+ return true;
}
- return 0;
+ return false;
}
/*
@@ -89,7 +93,7 @@ guest_walk_tables(struct vcpu *v, struct p2m_domain *p2m,
guest_l4e_t *l4p;
#endif
uint32_t gflags, rc;
- bool_t pse1G = 0, pse2M = 0;
+ unsigned int leaf_level;
p2m_query_t qt = P2M_ALLOC | P2M_UNSHARE;
#define AR_ACCUM_AND (_PAGE_USER | _PAGE_RW)
@@ -179,9 +183,7 @@ guest_walk_tables(struct vcpu *v, struct p2m_domain *p2m,
ar_and &= gflags;
ar_or |= gflags;
- pse1G = !!(gflags & _PAGE_PSE);
-
- if ( pse1G )
+ if ( gflags & _PAGE_PSE )
{
/* Generate a fake l1 table entry so callers don't all
* have to understand superpages. */
@@ -204,6 +206,7 @@ guest_walk_tables(struct vcpu *v, struct p2m_domain *p2m,
((va >> PAGE_SHIFT) & GUEST_L3_GFN_MASK));
gw->l1e = guest_l1e_from_gfn(start, flags);
gw->l2mfn = gw->l1mfn = INVALID_MFN;
+ leaf_level = 3;
goto leaf;
}
@@ -273,9 +276,7 @@ guest_walk_tables(struct vcpu *v, struct p2m_domain *p2m,
ar_and &= gflags;
ar_or |= gflags;
- pse2M = !!(gflags & _PAGE_PSE);
-
- if ( pse2M )
+ if ( gflags & _PAGE_PSE )
{
/* Special case: this guest VA is in a PSE superpage, so there's
* no guest l1e. We make one up so that the propagation code
@@ -309,6 +310,7 @@ guest_walk_tables(struct vcpu *v, struct p2m_domain *p2m,
gw->l1e = guest_l1e_from_gfn(start, flags);
#endif
gw->l1mfn = INVALID_MFN;
+ leaf_level = 2;
goto leaf;
}
@@ -340,6 +342,8 @@ guest_walk_tables(struct vcpu *v, struct p2m_domain *p2m,
ar_and &= gflags;
ar_or |= gflags;
+ leaf_level = 1;
+
leaf:
gw->pfec |= PFEC_page_present;
@@ -413,24 +417,33 @@ guest_walk_tables(struct vcpu *v, struct p2m_domain *p2m,
* success. Although the PRMs say higher-level _PAGE_ACCESSED bits
* get set whenever a lower-level PT is used, at least some hardware
* walkers behave this way. */
-#if GUEST_PAGING_LEVELS == 4 /* 64-bit only... */
- if ( set_ad_bits(l4p + guest_l4_table_offset(va), &gw->l4e, 0) )
- paging_mark_dirty(d, gw->l4mfn);
- if ( set_ad_bits(l3p + guest_l3_table_offset(va), &gw->l3e,
- (pse1G && (walk & PFEC_write_access))) )
- paging_mark_dirty(d, gw->l3mfn);
-#endif
- if ( !pse1G )
+ switch ( leaf_level )
{
+ default:
+ ASSERT_UNREACHABLE();
+ break;
+
+ case 1:
+ if ( set_ad_bits(l1p + guest_l1_table_offset(va), &gw->l1e,
+ (walk & PFEC_write_access) && leaf_level == 1) )
+ paging_mark_dirty(d, gw->l1mfn);
+ /* Fallthrough */
+
+ case 2:
if ( set_ad_bits(l2p + guest_l2_table_offset(va), &gw->l2e,
- (pse2M && (walk & PFEC_write_access))) )
+ (walk & PFEC_write_access) && leaf_level == 2) )
paging_mark_dirty(d, gw->l2mfn);
- if ( !pse2M )
- {
- if ( set_ad_bits(l1p + guest_l1_table_offset(va), &gw->l1e,
- (walk & PFEC_write_access)) )
- paging_mark_dirty(d, gw->l1mfn);
- }
+ /* Fallthrough */
+
+#if GUEST_PAGING_LEVELS == 4 /* 64-bit only... */
+ case 3:
+ if ( set_ad_bits(l3p + guest_l3_table_offset(va), &gw->l3e,
+ (walk & PFEC_write_access) && leaf_level == 3) )
+ paging_mark_dirty(d, gw->l3mfn);
+
+ if ( set_ad_bits(l4p + guest_l4_table_offset(va), &gw->l4e, 0) )
+ paging_mark_dirty(d, gw->l4mfn);
+#endif
}
out:
--
2.1.4
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