[PATCH v2] KVM: arm64: Remove stage 2 read fault check

[PATCH v2] KVM: arm64: Remove stage 2 read fault check

[Wei-Lin Chang]

In the non-NV case, read permission is always granted when mapping
stage-2, so checking for it doesn't bring much. On the other hand,
shadow stage-2 for NV guests could potentially have non-readable
mappings when we align the permissions with those that L1 set for L2, we
shouldn't be checking for read faults in this case either.

So just remove this check.

Suggested-by: Oliver Upton <oliver.upton@linux.dev>
Suggested-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Wei-Lin Chang <r09922117@csie.ntu.edu.tw>
---

Changes in v2, thanks to those listed in the Suggested-by tags:
  - remove the read fault check instead of skipping it for NV
  - Link to v1: https://lore.kernel.org/kvmarm/20250822031853.2007437-1-r09922117@csie.ntu.edu.tw/

---
 arch/arm64/kvm/mmu.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 1c78864767c5c..fb239cd9f7a67 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1508,11 +1508,6 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	exec_fault = kvm_vcpu_trap_is_exec_fault(vcpu);
 	VM_BUG_ON(write_fault && exec_fault);
 
-	if (fault_is_perm && !write_fault && !exec_fault) {
-		kvm_err("Unexpected L2 read permission error\n");
-		return -EFAULT;
-	}
-
 	if (!is_protected_kvm_enabled())
 		memcache = &vcpu->arch.mmu_page_cache;
 	else
-- 
2.50.1

Re: [PATCH v2] KVM: arm64: Remove stage 2 read fault check

[Oliver Upton]

On Mon, 08 Sep 2025 14:48:06 +0800, Wei-Lin Chang wrote:
> In the non-NV case, read permission is always granted when mapping
> stage-2, so checking for it doesn't bring much. On the other hand,
> shadow stage-2 for NV guests could potentially have non-readable
> mappings when we align the permissions with those that L1 set for L2, we
> shouldn't be checking for read faults in this case either.
> 
> So just remove this check.
> 
> [...]

Applied to fixes, thanks!

[1/1] KVM: arm64: Remove stage 2 read fault check
      https://git.kernel.org/kvmarm/kvmarm/c/756491dd8329

--
Best,
Oliver