[PATCH 01/20] KVM: arm64: Prefault host stage-2 entries on block split

[Vincent Donnefort]

From: Keir Fraser <keirf at google.com>

For the host stage-2 that is idmap, we can avoid lazy-mapping on block
splitting by propagate existing valid mappings to neighbouring entries
of the new table.

Co-developed-by: Quentin Perret <qperret at google.com>
Signed-off-by: Keir Fraser <keirf at google.com>
Signed-off-by: Vincent Donnefort <vdonnefort at google.com>

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index b74dd5ce1efd..34f78a58cded 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -1030,10 +1030,39 @@ static int stage2_map_walk_table_pre(const struct kvm_pgtable_visit_ctx *ctx,
 	return 0;
 }
 
+static void stage2_map_prefault_idmap(const struct kvm_pgtable_visit_ctx *ctx, kvm_pte_t *ptep)
+{
+	kvm_pte_t block_pte = ctx->old;
+	u64 pa;
+	int i;
+
+	if (!kvm_pte_valid(block_pte))
+		return;
+
+	pa = ALIGN_DOWN(ctx->addr, kvm_granule_size(ctx->level));
+	for (i = 0; i < PTRS_PER_PTE; ++i, ++ptep, pa += kvm_granule_size(ctx->level + 1)) {
+		kvm_pte_t pte = kvm_init_valid_leaf_pte(pa, block_pte, ctx->level + 1);
+
+		/*
+		 * Skip ptes in the range being modified by the caller if we're
+		 * installing last level entries. Otherwise, we need to
+		 * temporarily put in a valid mapping to make sure the
+		 * prefaulting logic is triggered on the next
+		 * stage2_map_walk_leaf(). This adds an unnecessary TLBI as
+		 * we'll presumably re-break the freshly installed block, but
+		 * that should happen very infrequently.
+		 */
+		if ((ctx->level < (KVM_PGTABLE_LAST_LEVEL - 1)) ||
+		    (pa < ctx->addr) || (pa >= ctx->end))
+			*ptep = pte;
+	}
+}
+
 static int stage2_map_walk_leaf(const struct kvm_pgtable_visit_ctx *ctx,
 				struct stage2_map_data *data)
 {
 	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
+	struct kvm_pgtable *pgt = data->mmu->pgt;
 	kvm_pte_t *childp, new;
 	int ret;
 
@@ -1051,6 +1080,9 @@ static int stage2_map_walk_leaf(const struct kvm_pgtable_visit_ctx *ctx,
 	if (!childp)
 		return -ENOMEM;
 
+	if (pgt->flags & KVM_PGTABLE_S2_IDMAP)
+		stage2_map_prefault_idmap(ctx, childp);
+
 	if (!stage2_try_break_pte(ctx, data->mmu)) {
 		mm_ops->put_page(childp);
 		return -EAGAIN;
-- 
2.55.0.508.g3f0d502094-goog