[PATCH 6.18.y 3/5] KVM: arm64: nv: Inject SEA if kvm_translate_vncr() can't resolve PFN

[Marc Zyngier <maz@kernel.org>]

From: Oliver Upton <oupton@kernel.org>

kvm_handle_vncr_abort() assumes that s1_walk_result conveys an abort
when kvm_translate_vncr() returns -EFAULT. This is not always the case
as it's possible to encounter 'late' failures on the output of S1
translation, e.g. a GFN outside of the memslots.

Fix it by preparing an external abort before returning from
kvm_translate_vncr(). Get rid of the BUG_ON() in the fault injection
path while at it.

Cc: stable@vger.kernel.org
Fixes: 2a359e072596 ("KVM: arm64: nv: Handle mapping of VNCR_EL2 at EL2")
Signed-off-by: Oliver Upton <oupton@kernel.org>
Link: https://patch.msgid.link/20260618234207.1063941-3-oupton@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
(cherry picked from commit 9f3e83345a56280efffe235c65593c7e544c0fcc)
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/include/asm/kvm_nested.h |  8 ++++++++
 arch/arm64/kvm/at.c                 |  8 --------
 arch/arm64/kvm/nested.c             | 10 ++++++----
 3 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_nested.h b/arch/arm64/include/asm/kvm_nested.h
index 4d7df3aa7dde6..6f768e361c894 100644
--- a/arch/arm64/include/asm/kvm_nested.h
+++ b/arch/arm64/include/asm/kvm_nested.h
@@ -353,6 +353,14 @@ struct s1_walk_result {
 	bool	failed;
 };
 
+static inline void fail_s1_walk(struct s1_walk_result *wr, u8 fst, bool s1ptw)
+{
+	wr->fst		= fst;
+	wr->ptw		= s1ptw;
+	wr->s2		= s1ptw;
+	wr->failed	= true;
+}
+
 int __kvm_translate_va(struct kvm_vcpu *vcpu, struct s1_walk_info *wi,
 		       struct s1_walk_result *wr, u64 va);
 int __kvm_find_s1_desc_level(struct kvm_vcpu *vcpu, u64 va, u64 ipa,
diff --git a/arch/arm64/kvm/at.c b/arch/arm64/kvm/at.c
index 7a3d07ee6a76c..2bdc49bef8613 100644
--- a/arch/arm64/kvm/at.c
+++ b/arch/arm64/kvm/at.c
@@ -10,14 +10,6 @@
 #include <asm/kvm_hyp.h>
 #include <asm/kvm_mmu.h>
 
-static void fail_s1_walk(struct s1_walk_result *wr, u8 fst, bool s1ptw)
-{
-	wr->fst		= fst;
-	wr->ptw		= s1ptw;
-	wr->s2		= s1ptw;
-	wr->failed	= true;
-}
-
 #define S1_MMU_DISABLED		(-127)
 
 static int get_ia_size(struct s1_walk_info *wi)
diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
index 7aabddfd895ef..ece0fd268ecc2 100644
--- a/arch/arm64/kvm/nested.c
+++ b/arch/arm64/kvm/nested.c
@@ -1247,15 +1247,19 @@ static int kvm_translate_vncr(struct kvm_vcpu *vcpu, bool *is_gmem)
 
 	gfn = vt->wr.pa >> PAGE_SHIFT;
 	memslot = gfn_to_memslot(vcpu->kvm, gfn);
-	if (!memslot)
+	if (!memslot) {
+		fail_s1_walk(&vt->wr, ESR_ELx_FSC_EXTABT, false);
 		return -EFAULT;
+	}
 
 	*is_gmem = kvm_slot_has_gmem(memslot);
 	if (!*is_gmem) {
 		pfn = __kvm_faultin_pfn(memslot, gfn, write_fault ? FOLL_WRITE : 0,
 					&writable, &page);
-		if (is_error_noslot_pfn(pfn))
+		if (is_error_noslot_pfn(pfn)) {
+			fail_s1_walk(&vt->wr, ESR_ELx_FSC_EXTABT, false);
 			return -EFAULT;
+		}
 	} else {
 		ret = kvm_gmem_get_pfn(vcpu->kvm, memslot, gfn, &pfn, &page, NULL);
 		if (ret) {
@@ -1382,8 +1386,6 @@ int kvm_handle_vncr_abort(struct kvm_vcpu *vcpu)
 			 * Translation failed, inject the corresponding
 			 * exception back to EL2.
 			 */
-			BUG_ON(!vt->wr.failed);
-
 			esr &= ~ESR_ELx_FSC;
 			esr |= FIELD_PREP(ESR_ELx_FSC, vt->wr.fst);
 
-- 
2.47.3