From: Yanan Wang <[email protected]> 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 <[email protected]> [maz: update commit message, add comment in the code] Signed-off-by: Marc Zyngier <[email protected]> Acked-by: Will Deacon <[email protected]> Link: https://lore.kernel.org/r/[email protected] --- 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 0271b4a3b9fe..2beba1dc40ec 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; -- 2.28.0 _______________________________________________ kvmarm mailing list [email protected] https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
