Subject: [PATCH 6/7] KVM: arm64: Handle stage-2 faults on stage-1 page-table walks earlier

From: Will Deacon <[email-masked]>
Date: Fri, 24 Jul 2020 15:35:05 +0100

Stage-2 faults on stage-1 page-table walks can occur on both the I-side
and the D-side. It is IMPLEMENTATATION DEFINED whether they are reported
as reads or writes and, in the case that they are generated by an AT
instruction, they are reported with the CM bit set.

All of this deeply confuses the logic in kvm_handle_guest_abort();
userspace may or may not see the fault, depending on whether it occurs
on the data or the instruction side, and an AT instruction may be skipped
if the translation tables are held in a read-only memslot.

Move the handling of stage-2 faults on stage-1 page-table walks earlier
so that they consistently result in either a data or an instruction abort
being re-injected back to the guest.

Cc: Marc Zyngier <[email-masked]>
Cc: Quentin Perret <[email-masked]>
Signed-off-by: Will Deacon <[email-masked]>
---
 arch/arm64/kvm/mmu.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index adb933ecd177..9e72e7f4a2c2 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -2124,6 +2124,11 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
 			goto out;
 		}
 
+		if (kvm_vcpu_dabt_iss1tw(vcpu)) {
+			ret = -ENXIO;
+			goto out;
+		}
+
 		/*
 		 * Check for a cache maintenance operation. Since we
 		 * ended-up here, we know it is outside of any memory
@@ -2157,11 +2162,6 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
 			goto out_unlock;
 		}
 
-		if (kvm_vcpu_dabt_iss1tw(vcpu)) {
-			ret = -ENXIO;
-			goto out;
-		}
-
 		ret = io_mem_abort(vcpu, run, fault_ipa);
 		goto out_unlock;
 	}
-- 
2.28.0.rc0.142.g3c755180ce-goog

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