[PATCH v3 7/7] KVM: arm64: Use TLBI range-based intructions for unmap

[Raghavendra Rao Ananta]

The current implementation of the stage-2 unmap walker traverses
the given range and, as a part of break-before-make, performs
TLB invalidations with a DSB for every PTE. A multitude of this
combination could cause a performance bottleneck.

Hence, if the system supports FEAT_TLBIRANGE, defer the TLB
invalidations until the entire walk is finished, and then
use range-based instructions to invalidate the TLBs in one go.
Condition this upon S2FWB in order to avoid walking the page-table
again to perform the CMOs after issuing the TLBI.

Signed-off-by: Raghavendra Rao Ananta <rananta at google.com>
Suggested-by: Oliver Upton <oliver.upton at linux.dev>
---
 arch/arm64/kvm/hyp/pgtable.c | 33 +++++++++++++++++++++++++++++----
 1 file changed, 29 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 3f136e35feb5e..bcb748e3566c7 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -987,10 +987,16 @@ int kvm_pgtable_stage2_set_owner(struct kvm_pgtable *pgt, u64 addr, u64 size,
 	return ret;
 }
 
+struct stage2_unmap_data {
+	struct kvm_pgtable *pgt;
+	bool skip_pte_tlbis;
+};
+
 static int stage2_unmap_walker(const struct kvm_pgtable_visit_ctx *ctx,
 			       enum kvm_pgtable_walk_flags visit)
 {
-	struct kvm_pgtable *pgt = ctx->arg;
+	struct stage2_unmap_data *unmap_data = ctx->arg;
+	struct kvm_pgtable *pgt = unmap_data->pgt;
 	struct kvm_s2_mmu *mmu = pgt->mmu;
 	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
 	kvm_pte_t *childp = NULL;
@@ -1018,7 +1024,7 @@ static int stage2_unmap_walker(const struct kvm_pgtable_visit_ctx *ctx,
 	 * block entry and rely on the remaining portions being faulted
 	 * back lazily.
 	 */
-	stage2_put_pte(ctx, mmu, mm_ops, false);
+	stage2_put_pte(ctx, mmu, mm_ops, unmap_data->skip_pte_tlbis);
 
 	if (need_flush && mm_ops->dcache_clean_inval_poc)
 		mm_ops->dcache_clean_inval_poc(kvm_pte_follow(ctx->old, mm_ops),
@@ -1032,13 +1038,32 @@ static int stage2_unmap_walker(const struct kvm_pgtable_visit_ctx *ctx,
 
 int kvm_pgtable_stage2_unmap(struct kvm_pgtable *pgt, u64 addr, u64 size)
 {
+	int ret;
+	struct stage2_unmap_data unmap_data = {
+		.pgt = pgt,
+		/*
+		 * If FEAT_TLBIRANGE is implemented, defer the individial PTE
+		 * TLB invalidations until the entire walk is finished, and
+		 * then use the range-based TLBI instructions to do the
+		 * invalidations. Condition this upon S2FWB in order to avoid
+		 * a page-table walk again to perform the CMOs after TLBI.
+		 */
+		.skip_pte_tlbis = system_supports_tlb_range() &&
+					stage2_has_fwb(pgt),
+	};
 	struct kvm_pgtable_walker walker = {
 		.cb	= stage2_unmap_walker,
-		.arg	= pgt,
+		.arg	= &unmap_data,
 		.flags	= KVM_PGTABLE_WALK_LEAF | KVM_PGTABLE_WALK_TABLE_POST,
 	};
 
-	return kvm_pgtable_walk(pgt, addr, size, &walker);
+	ret = kvm_pgtable_walk(pgt, addr, size, &walker);
+	if (unmap_data.skip_pte_tlbis)
+		/* Perform the deferred TLB invalidations */
+		kvm_call_hyp(__kvm_tlb_flush_vmid_range, pgt->mmu,
+				addr, addr + size);
+
+	return ret;
 }
 
 struct stage2_attr_data {
-- 
2.40.0.634.g4ca3ef3211-goog