KVM: arm64: nv: Check S2 limits based on implemented PA size

check_base_s2_limits() checks the validity of SL0 and inputsize against
ia_size (inputsize again!) but the pseudocode from DDI0487 G.a
AArch64.TranslationTableWalk() says that we should check against the
implemented PA size.

We would otherwise fail to walk S2 with a valid configuration. E.g.,
granule size = 4KB, inputsize = 40 bits, initial lookup level = 0 (no
concatenation) on a system with 48 bits PA range supported is allowed by
architecture.

Fix it by obtaining PA size by kvm_get_pa_bits(). Note that
kvm_get_pa_bits() returns the fixed limit now and should eventually reflect
the per VM PARange (one day!). Given that the configured PARange should not
be greater that kvm_ipa_limit, it at least fixes the problem described
above.

While at it, inject a level 0 translation fault to guest if
check_base_s2_limits() fails, as per the pseudocode.

Fixes: 61e30b9 ("KVM: arm64: nv: Implement nested Stage-2 page table walk logic")
Signed-off-by: Zenghui Yu (Huawei) <zenghui.yu@linux.dev>
Link: https://patch.msgid.link/20260225173515.20490-2-zenghui.yu@linux.dev
Signed-off-by: Marc Zyngier <maz@kernel.org>

Author: Zenghui Yu (Huawei)

arch/arm64/kvm/nested.c

@@ -152,31 +152,31 @@ static int get_ia_size(struct s2_walk_info *wi)
 	return 64 - wi->t0sz;
 }
 
-static int check_base_s2_limits(struct s2_walk_info *wi,
+static int check_base_s2_limits(struct kvm_vcpu *vcpu, struct s2_walk_info *wi,
 				int level, int input_size, int stride)
 {
-	int start_size, ia_size;
+	int start_size, pa_max;
 
-	ia_size = get_ia_size(wi);
+	pa_max = kvm_get_pa_bits(vcpu->kvm);
 
 	/* Check translation limits */
 	switch (BIT(wi->pgshift)) {
 	case SZ_64K:
-		if (level == 0 || (level == 1 && ia_size <= 42))
+		if (level == 0 || (level == 1 && pa_max <= 42))
 			return -EFAULT;
 		break;
 	case SZ_16K:
-		if (level == 0 || (level == 1 && ia_size <= 40))
+		if (level == 0 || (level == 1 && pa_max <= 40))
 			return -EFAULT;
 		break;
 	case SZ_4K:
-		if (level < 0 || (level == 0 && ia_size <= 42))
+		if (level < 0 || (level == 0 && pa_max <= 42))
 			return -EFAULT;
 		break;
 	}
 
 	/* Check input size limits */
-	if (input_size > ia_size)
+	if (input_size > pa_max)
 		return -EFAULT;
 
 	/* Check number of entries in starting level table */
@@ -269,9 +269,11 @@ static int walk_nested_s2_pgd(struct kvm_vcpu *vcpu, phys_addr_t ipa,
 	if (input_size > 48 || input_size < 25)
 		return -EFAULT;
 
-	ret = check_base_s2_limits(wi, level, input_size, stride);
-	if (WARN_ON(ret))
+	ret = check_base_s2_limits(vcpu, wi, level, input_size, stride);
+	if (WARN_ON(ret)) {
+		out->esr = compute_fsc(0, ESR_ELx_FSC_FAULT);
 		return ret;
+	}
 
 	base_lower_bound = 3 + input_size - ((3 - level) * stride +
 			   wi->pgshift);