From 5c646b7e1d8bcb12317426287c516dfa4c5171c2 Mon Sep 17 00:00:00 2001 From: Yanan Wang Date: Wed, 2 Dec 2020 04:10:32 +0800 Subject: [PATCH] KVM: arm64: Fix memory leak on stage2 update of a valid PTE When installing a new leaf PTE onto an invalid ptep, we need to get_page(ptep) to account for the new mapping. However, simply updating a valid PTE shouldn't result in any additional refcounting, as there is new mapping. This otherwise results in a page being forever wasted. Address this by fixing-up the refcount in stage2_map_walker_try_leaf() if the PTE was already valid, balancing out the later get_page() in stage2_map_walk_leaf(). Signed-off-by: Yanan Wang [maz: update commit message, add comment in the code] Signed-off-by: Marc Zyngier Acked-by: Will Deacon Link: https://lore.kernel.org/r/20201201201034.116760-2-wangyanan55@huawei.com --- arch/arm64/kvm/hyp/pgtable.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c index 0271b4a..2beba1d 100644 --- a/arch/arm64/kvm/hyp/pgtable.c +++ b/arch/arm64/kvm/hyp/pgtable.c @@ -470,6 +470,15 @@ static bool stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level, if (!kvm_block_mapping_supported(addr, end, phys, level)) return false; + /* + * If the PTE was already valid, drop the refcount on the table + * early, as it will be bumped-up again in stage2_map_walk_leaf(). + * This ensures that the refcount stays constant across a valid to + * valid PTE update. + */ + if (kvm_pte_valid(*ptep)) + put_page(virt_to_page(ptep)); + if (kvm_set_valid_leaf_pte(ptep, phys, data->attr, level)) goto out; -- 2.7.4