It is possible that a table page remains visible to another thread until
the next rcu synchronization event. To that end, we cannot drop the last
page reference synchronous with post-order traversal for a parallel
table walk.
Schedule an rcu callback to clean up the child table page for parallel
walks.
Signed-off-by: Oliver Upton <oupton@xxxxxxxxxx>
---
arch/arm64/include/asm/kvm_pgtable.h | 3 ++
arch/arm64/kvm/hyp/pgtable.c | 24 +++++++++++++--
arch/arm64/kvm/mmu.c | 44 +++++++++++++++++++++++++++-
3 files changed, 67 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 74955aba5918..52e55e00f0ca 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -81,6 +81,8 @@ static inline bool kvm_level_supports_block_mapping(u32 level)
* @put_page: Decrement the refcount on a page. When the
* refcount reaches 0 the page is automatically
* freed.
+ * @free_table: Drop the last page reference, possibly in the
+ * next RCU sync if doing a shared walk.
* @page_count: Return the refcount of a page.
* @phys_to_virt: Convert a physical address into a virtual
* address mapped in the current context.
@@ -98,6 +100,7 @@ struct kvm_pgtable_mm_ops {
void (*get_page)(void *addr);
void (*put_page)(void *addr);
int (*page_count)(void *addr);
+ void (*free_table)(void *addr, bool shared);
void* (*phys_to_virt)(phys_addr_t phys);
phys_addr_t (*virt_to_phys)(void *addr);
void (*dcache_clean_inval_poc)(void *addr, size_t size);
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 121818d4c33e..a9a48edba63b 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -147,12 +147,19 @@ static inline void kvm_pgtable_walk_end(void)
{}
#define kvm_dereference_ptep rcu_dereference_raw
+
+static inline void kvm_pgtable_destroy_barrier(void)
+{}
+
#else
#define kvm_pgtable_walk_begin rcu_read_lock
#define kvm_pgtable_walk_end rcu_read_unlock
#define kvm_dereference_ptep rcu_dereference
+
+#define kvm_pgtable_destroy_barrier rcu_barrier
+
#endif
static kvm_pte_t *kvm_pte_follow(kvm_pte_t pte, struct kvm_pgtable_mm_ops *mm_ops)
@@ -1063,7 +1070,12 @@ static int stage2_map_walk_table_post(u64 addr, u64 end, u32 level,
childp = kvm_pte_follow(*old, mm_ops);
}
- mm_ops->put_page(childp);
+ /*
+ * If we do not have exclusive access to the page tables it is possible
+ * the unlinked table remains visible to another thread until the next
+ * rcu synchronization.
+ */
+ mm_ops->free_table(childp, shared);
mm_ops->put_page(ptep);
return ret;
@@ -1203,7 +1215,7 @@ static int stage2_unmap_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
kvm_granule_size(level));
if (childp)
- mm_ops->put_page(childp);
+ mm_ops->free_table(childp, shared);
return 0;
}
@@ -1433,7 +1445,7 @@ static int stage2_free_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
mm_ops->put_page(ptep);
if (kvm_pte_table(*old, level))
- mm_ops->put_page(kvm_pte_follow(*old, mm_ops));
+ mm_ops->free_table(kvm_pte_follow(*old, mm_ops), shared);
return 0;
}
@@ -1452,4 +1464,10 @@ void kvm_pgtable_stage2_destroy(struct kvm_pgtable *pgt)
pgd_sz = kvm_pgd_pages(pgt->ia_bits, pgt->start_level) * PAGE_SIZE;
pgt->mm_ops->free_pages_exact(pgt->pgd, pgd_sz);
pgt->pgd = NULL;
+
+ /*
+ * Guarantee that all unlinked subtrees associated with the stage2 page
+ * table have also been freed before returning.
+ */
+ kvm_pgtable_destroy_barrier();
}
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index cc6ed6b06ec2..6ecf37009c21 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -98,9 +98,50 @@ static bool kvm_is_device_pfn(unsigned long pfn)
static void *stage2_memcache_zalloc_page(void *arg)
{
struct kvm_mmu_caches *mmu_caches = arg;
+ struct stage2_page_header *hdr;
+ void *addr;
/* Allocated with __GFP_ZERO, so no need to zero */
- return kvm_mmu_memory_cache_alloc(&mmu_caches->page_cache);
+ addr = kvm_mmu_memory_cache_alloc(&mmu_caches->page_cache);
+ if (!addr)
+ return NULL;
+
+ hdr = kvm_mmu_memory_cache_alloc(&mmu_caches->header_cache);
+ if (!hdr) {
+ free_page((unsigned long)addr);
+ return NULL;
+ }
+
+ hdr->page = virt_to_page(addr);
+ set_page_private(hdr->page, (unsigned long)hdr);
+ return addr;
+}
+
+static void stage2_free_page_now(struct stage2_page_header *hdr)
+{
+ WARN_ON(page_ref_count(hdr->page) != 1);
+
+ __free_page(hdr->page);
+ kmem_cache_free(stage2_page_header_cache, hdr);
+}
+
+static void stage2_free_page_rcu_cb(struct rcu_head *head)
+{
+ struct stage2_page_header *hdr = container_of(head, struct stage2_page_header,
+ rcu_head);
+
+ stage2_free_page_now(hdr);
+}
+
+static void stage2_free_table(void *addr, bool shared)
+{
+ struct page *page = virt_to_page(addr);
+ struct stage2_page_header *hdr = (struct stage2_page_header *)page_private(page);
+
+ if (shared)
+ call_rcu(&hdr->rcu_head, stage2_free_page_rcu_cb);
+ else
+ stage2_free_page_now(hdr);
}
static void *kvm_host_zalloc_pages_exact(size_t size)
@@ -613,6 +654,7 @@ static struct kvm_pgtable_mm_ops kvm_s2_mm_ops = {
.free_pages_exact = free_pages_exact,
.get_page = kvm_host_get_page,
.put_page = kvm_host_put_page,
+ .free_table = stage2_free_table,
.page_count = kvm_host_page_count,
.phys_to_virt = kvm_host_va,
.virt_to_phys = kvm_host_pa,
--
2.36.0.rc0.470.gd361397f0d-goog
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