[RFC PATCH 2/2] KVM: arm64: nv: Use kvm_stage2_unmap_all() for shadow S2 teardown

[Haseeb Ashraf]

From: Haseeb Ashraf <haseeb.ashraf@xxxxxxxxxxx>

kvm_nested_s2_unmap() and the pending unmap that is completed at vcpu
entry both drop a complete shadow stage-2 by unmapping its whole IPA
range chunk by chunk, with the same cost for an empty table as the
TLBI VMALLS12E1IS handler: 262144 unmap calls per MMU with 4kB pages
and a 48-bit PARange.

kvm_nested_s2_unmap() is used when emulating TLBI ALLE1IS and when the
whole VM is unmapped. The pending unmap runs on the first entry after
a shadow MMU has been recycled for a different context, which a guest
hypervisor running more contexts than there are shadow MMUs can
trigger repeatedly.

Switch both to kvm_stage2_unmap_all(). The may_block rules are
unchanged: kvm_nested_s2_unmap() forwards its argument, and the
pending unmap, which only holds mmu_lock, still allows blocking. The
VNCR invalidation and the synchronous completion of the pending unmap
are left as they are.

Unmaps of a canonical IPA range, such as MMU notifier invalidations
and memslot removal, no longer go through kvm_nested_s2_unmap() since
the guest stage-2 tracking was introduced, and are not affected.

Signed-off-by: Haseeb Ashraf <haseeb.ashraf@xxxxxxxxxxx>
---
 arch/arm64/kvm/nested.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
index 4d83281a7a28..875eb9c312f9 100644
--- a/arch/arm64/kvm/nested.c
+++ b/arch/arm64/kvm/nested.c
@@ -1441,7 +1441,7 @@ void kvm_nested_s2_unmap(struct kvm *kvm, bool may_block)
 		struct kvm_s2_mmu *mmu = kvm->arch.nested_mmus[i];
 
 		if (kvm_s2_mmu_valid(mmu))
-			kvm_stage2_unmap_range(mmu, 0, kvm_phys_size(mmu), may_block);
+			kvm_stage2_unmap_all(mmu, may_block);
 	}
 
 	kvm_invalidate_vncr_ipa_all(kvm);
@@ -2160,7 +2160,7 @@ void check_nested_vcpu_requests(struct kvm_vcpu *vcpu)
 
 		write_lock(&vcpu->kvm->mmu_lock);
 		if (mmu->pending_unmap) {
-			kvm_stage2_unmap_range(mmu, 0, kvm_phys_size(mmu), true);
+			kvm_stage2_unmap_all(mmu, true);
 			mmu->pending_unmap = false;
 		}
 		write_unlock(&vcpu->kvm->mmu_lock);
-- 
2.43.0