[PATCH v3 03/15] KVM: arm64: Refcount hyp stage-1 pgtable pages

Quentin Perret
2021-12-01T17:06:42Z

To prepare the ground for allowing hyp stage-1 mappings to be removed at
run-time, update the KVM page-table code to maintain a correct refcount
using the ->{get,put}_page() function callbacks.

Signed-off-by: Quentin Perret <qperret@google.com>
---
arch/arm64/kvm/hyp/pgtable.c | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index f8ceebe4982e..768a58835153 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -408,8 +408,10 @@ static bool hyp_map_walker_try_leaf(u64 addr, u64 end, u32 level,
return false;

new = kvm_init_valid_leaf_pte(phys, data->attr, level);
- if (hyp_pte_needs_update(old, new))
+ if (hyp_pte_needs_update(old, new)) {
smp_store_release(ptep, new);
+ data->mm_ops->get_page(ptep);
+ }

data->phys += granule;
return true;
@@ -433,6 +435,7 @@ static int hyp_map_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
return -ENOMEM;

kvm_set_table_pte(ptep, childp, mm_ops);
+ mm_ops->get_page(ptep);
return 0;
}

@@ -482,8 +485,16 @@ static int hyp_free_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
enum kvm_pgtable_walk_flags flag, void * const arg)
{
struct kvm_pgtable_mm_ops *mm_ops = arg;
+ kvm_pte_t pte = *ptep;
+
+ if (!kvm_pte_valid(pte))
+ return 0;
+
+ mm_ops->put_page(ptep);
+
+ if (kvm_pte_table(pte, level))
+ mm_ops->put_page(kvm_pte_follow(pte, mm_ops));

- mm_ops->put_page((void *)kvm_pte_follow(*ptep, mm_ops));
return 0;
}

@@ -491,7 +502,7 @@ void kvm_pgtable_hyp_destroy(struct kvm_pgtable *pgt)
{
struct kvm_pgtable_walker walker = {
.cb = hyp_free_walker,
- .flags = KVM_PGTABLE_WALK_TABLE_POST,
+ .flags = KVM_PGTABLE_WALK_LEAF | KVM_PGTABLE_WALK_TABLE_POST,
.arg = pgt->mm_ops,
};

--
2.34.0.rc2.393.gf8c9666880-goog