[PATCH v3 15/15] KVM: MMU: use rcu functions to access the pointer

Xiao Guangrong
2013-10-23T13:30:14Z

Use rcu_assign_pointer() to update all the pointer in desc
and use rcu_dereference() to lockless read the pointer

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
---
arch/x86/kvm/mmu.c | 46 ++++++++++++++++++++++++++++------------------
1 file changed, 28 insertions(+), 18 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 3e4b941..68dac26 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -937,12 +937,23 @@ static void pte_list_desc_ctor(void *p)
desc->more = NULL;
}

+#define rcu_assign_pte_list(pte_list_p, value) \
+ rcu_assign_pointer(*(unsigned long __rcu **)(pte_list_p), \
+ (unsigned long *)(value))
+
+#define rcu_assign_desc_more(morep, value) \
+ rcu_assign_pointer(*(unsigned long __rcu **)&morep, \
+ (unsigned long *)value)
+
+#define rcu_assign_spte(sptep, value) \
+ rcu_assign_pointer(*(u64 __rcu **)&sptep, (u64 *)value)
+
static void desc_mark_nulls(unsigned long *pte_list, struct pte_list_desc *desc)
{
unsigned long marker;

marker = (unsigned long)pte_list | 1UL;
- desc->more = (struct pte_list_desc *)marker;
+ rcu_assign_desc_more(desc->more, (struct pte_list_desc *)marker);
}

static bool desc_is_a_nulls(struct pte_list_desc *desc)
@@ -999,10 +1010,6 @@ static int count_spte_number(struct pte_list_desc *desc)
return first_free + desc_num * PTE_LIST_EXT;
}

-#define rcu_assign_pte_list(pte_list_p, value) \
- rcu_assign_pointer(*(unsigned long __rcu **)(pte_list_p), \
- (unsigned long *)(value))
-
/*
* Pte mapping structures:
*
@@ -1029,8 +1036,8 @@ static int pte_list_add(struct kvm_vcpu *vcpu, u64 *spte,
if (!(*pte_list & 1)) {
rmap_printk("pte_list_add: %p %llx 1->many\n", spte, *spte);
desc = mmu_alloc_pte_list_desc(vcpu);
- desc->sptes[0] = (u64 *)*pte_list;
- desc->sptes[1] = spte;
+ rcu_assign_spte(desc->sptes[0], *pte_list);
+ rcu_assign_spte(desc->sptes[1], spte);
desc_mark_nulls(pte_list, desc);
rcu_assign_pte_list(pte_list, (unsigned long)desc | 1);
return 1;
@@ -1043,13 +1050,13 @@ static int pte_list_add(struct kvm_vcpu *vcpu, u64 *spte,
if (desc->sptes[PTE_LIST_EXT - 1]) {
struct pte_list_desc *new_desc;
new_desc = mmu_alloc_pte_list_desc(vcpu);
- new_desc->more = desc;
+ rcu_assign_desc_more(new_desc->more, desc);
desc = new_desc;
rcu_assign_pte_list(pte_list, (unsigned long)desc | 1);
}

free_pos = find_first_free(desc);
- desc->sptes[free_pos] = spte;
+ rcu_assign_spte(desc->sptes[free_pos], spte);
return count_spte_number(desc) - 1;
}

@@ -1067,8 +1074,8 @@ pte_list_desc_remove_entry(unsigned long *pte_list,
* Move the entry from the first desc to this position we want
* to remove.
*/
- desc->sptes[i] = first_desc->sptes[last_used];
- first_desc->sptes[last_used] = NULL;
+ rcu_assign_spte(desc->sptes[i], first_desc->sptes[last_used]);
+ rcu_assign_spte(first_desc->sptes[last_used], NULL);

/* No valid entry in this desc, we can free this desc now. */
if (!first_desc->sptes[0]) {
@@ -1080,7 +1087,7 @@ pte_list_desc_remove_entry(unsigned long *pte_list,
WARN_ON(desc_is_a_nulls(next_desc));

mmu_free_pte_list_desc(first_desc);
- *pte_list = (unsigned long)next_desc | 1ul;
+ rcu_assign_pte_list(pte_list, (unsigned long)next_desc | 1ul);
return;
}

@@ -1089,8 +1096,8 @@ pte_list_desc_remove_entry(unsigned long *pte_list,
* then the desc can be freed.
*/
if (!first_desc->sptes[1] && desc_is_a_nulls(first_desc->more)) {
- *pte_list = (unsigned long)first_desc->sptes[0];
- first_desc->sptes[0] = NULL;
+ rcu_assign_pte_list(pte_list, first_desc->sptes[0]);
+ rcu_assign_spte(first_desc->sptes[0], NULL);
mmu_free_pte_list_desc(first_desc);
}
}
@@ -1112,7 +1119,7 @@ static void pte_list_remove(u64 *spte, unsigned long *pte_list)
pr_err("pte_list_remove: %p 1->BUG\n", spte);
BUG();
}
- *pte_list = 0;
+ rcu_assign_pte_list(pte_list, 0);
return;
}

@@ -1184,9 +1191,12 @@ restart:
* used in the rmap when a spte is removed. Otherwise the
* moved entry will be missed.
*/
- for (i = PTE_LIST_EXT - 1; i >= 0; i--)
- if (desc->sptes[i])
- fn(desc->sptes[i]);
+ for (i = PTE_LIST_EXT - 1; i >= 0; i--) {
+ u64 *sptep = rcu_dereference(desc->sptes[i]);
+
+ if (sptep)
+ fn(sptep);
+ }

desc = rcu_dereference(desc->more);

--
1.8.1.4