[PATCH 01/14] KVM: arm64: Add a helper to tear down unlinked stage-2 subtrees

Oliver Upton
2022-08-30T19:41:59Z

A subsequent change to KVM will move the tear down of an unlinked
stage-2 subtree out of the critical path of the break-before-make
sequence.

Introduce a new helper for tearing down unlinked stage-2 subtrees.
Leverage the existing stage-2 free walkers to do so, with a deep call
into __kvm_pgtable_walk() as the subtree is no longer reachable from the
root.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
arch/arm64/include/asm/kvm_pgtable.h | 11 +++++++++++
arch/arm64/kvm/hyp/pgtable.c | 26 ++++++++++++++++++++++++++
2 files changed, 37 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 9f339dffbc1a..d71fb92dc913 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -316,6 +316,17 @@ int __kvm_pgtable_stage2_init(struct kvm_pgtable *pgt, struct kvm_s2_mmu *mmu,
*/
void kvm_pgtable_stage2_destroy(struct kvm_pgtable *pgt);

+/**
+ * kvm_pgtable_stage2_free_removed() - Free a removed stage-2 paging structure.
+ * @pgtable: Unlinked stage-2 paging structure to be freed.
+ * @level: Level of the stage-2 paging structure to be freed.
+ * @arg: Page-table structure initialised by kvm_pgtable_stage2_init*()
+ *
+ * The page-table is assumed to be unreachable by any hardware walkers prior to
+ * freeing and therefore no TLB invalidation is performed.
+ */
+void kvm_pgtable_stage2_free_removed(void *pgtable, u32 level, void *arg);
+
/**
* kvm_pgtable_stage2_map() - Install a mapping in a guest stage-2 page-table.
* @pgt: Page-table structure initialised by kvm_pgtable_stage2_init*().
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 2cb3867eb7c2..d8127c25424c 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -1233,3 +1233,29 @@ void kvm_pgtable_stage2_destroy(struct kvm_pgtable *pgt)
pgt->mm_ops->free_pages_exact(pgt->pgd, pgd_sz);
pgt->pgd = NULL;
}
+
+void kvm_pgtable_stage2_free_removed(void *pgtable, u32 level, void *arg)
+{
+ struct kvm_pgtable *pgt = (struct kvm_pgtable *)arg;
+ kvm_pte_t *ptep = (kvm_pte_t *)pgtable;
+ struct kvm_pgtable_walker walker = {
+ .cb = stage2_free_walker,
+ .flags = KVM_PGTABLE_WALK_LEAF |
+ KVM_PGTABLE_WALK_TABLE_POST,
+ .arg = pgt->mm_ops,
+ };
+ struct kvm_pgtable_walk_data data = {
+ .pgt = pgt,
+ .walker = &walker,
+
+ /*
+ * At this point the IPA really doesn't matter, as the page
+ * table being traversed has already been removed from the stage
+ * 2. Set an appropriate range to cover the entire page table.
+ */
+ .addr = 0,
+ .end = kvm_granule_size(level),
+ };
+
+ WARN_ON(__kvm_pgtable_walk(&data, ptep, level));
+}
--
2.37.2.672.g94769d06f0-goog