[PATCH v5 4/7] KVM: arm64: Skip pKVM stage-2 flush when FWB is enabled

[Fuad Tabba <fuad.tabba@linux.dev>]

pkvm_pgtable_stage2_flush() cleans the D-cache for every mapping in the
range even on hardware with stage-2 Force Write-Back, where FWB keeps
guest memory coherent to the PoC and the maintenance is unnecessary. The
generic kvm_pgtable_stage2_flush() returns early in that case, but the
pKVM MMU does not, so it needlessly cleans the whole range on, e.g.,
every set/way trap.

Return early when FWB is enabled, matching the generic walker.

Fixes: e912efed485a ("KVM: arm64: Introduce the EL1 pKVM MMU")
Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
---
 arch/arm64/kvm/pkvm.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/arm64/kvm/pkvm.c b/arch/arm64/kvm/pkvm.c
index f70c601dcf4c..ba6570e37545 100644
--- a/arch/arm64/kvm/pkvm.c
+++ b/arch/arm64/kvm/pkvm.c
@@ -518,6 +518,10 @@ int pkvm_pgtable_stage2_flush(struct kvm_pgtable *pgt, u64 addr, u64 size)
 	struct pkvm_mapping *mapping;
 
 	lockdep_assert_held(&kvm->mmu_lock);
+
+	if (cpus_have_final_cap(ARM64_HAS_STAGE2_FWB))
+		return 0;
+
 	for_each_mapping_in_range_safe(pgt, addr, addr + size, mapping) {
 		if (!mapping->nc)
 			__clean_dcache_guest_page(pfn_to_kaddr(mapping->pfn),
-- 
2.39.5