RISC-V: KVM: Fix inclusion of Smnpm in the guest ISA bitmap

The Smnpm extension requires special handling because the guest ISA
extension maps to a different extension (Ssnpm) on the host side.
commit 1851e78 ("RISC-V: KVM: Allow Smnpm and Ssnpm extensions for
guests") missed that the vcpu->arch.isa bit is based only on the host
extension, so currently both KVM_RISCV_ISA_EXT_{SMNPM,SSNPM} map to
vcpu->arch.isa[RISCV_ISA_EXT_SSNPM]. This does not cause any problems
for the guest, because both extensions are force-enabled anyway when the
host supports Ssnpm, but prevents checking for (guest) Smnpm in the SBI
FWFT logic.

Redefine kvm_isa_ext_arr to look up the guest extension, since only the
guest -> host mapping is unambiguous. Factor out the logic for checking
for host support of an extension, so this special case only needs to be
handled in one place, and be explicit about which variables hold a host
vs a guest ISA extension.

Fixes: 1851e78 ("RISC-V: KVM: Allow Smnpm and Ssnpm extensions for guests")
Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20250111004702.2813013-2-samuel.holland@sifive.com
Signed-off-by: Anup Patel <anup@brainfault.org>

Author: SiFiveHolland

arch/riscv/kvm/vcpu_onereg.c

@@ -23,7 +23,7 @@
 #define KVM_ISA_EXT_ARR(ext)		\
 [KVM_RISCV_ISA_EXT_##ext] = RISCV_ISA_EXT_##ext
 
-/* Mapping between KVM ISA Extension ID & Host ISA extension ID */
+/* Mapping between KVM ISA Extension ID & guest ISA extension ID */
 static const unsigned long kvm_isa_ext_arr[] = {
 	/* Single letter extensions (alphabetically sorted) */
 	[KVM_RISCV_ISA_EXT_A] = RISCV_ISA_EXT_a,
@@ -35,7 +35,7 @@ static const unsigned long kvm_isa_ext_arr[] = {
 	[KVM_RISCV_ISA_EXT_M] = RISCV_ISA_EXT_m,
 	[KVM_RISCV_ISA_EXT_V] = RISCV_ISA_EXT_v,
 	/* Multi letter extensions (alphabetically sorted) */
-	[KVM_RISCV_ISA_EXT_SMNPM] = RISCV_ISA_EXT_SSNPM,
+	KVM_ISA_EXT_ARR(SMNPM),
 	KVM_ISA_EXT_ARR(SMSTATEEN),
 	KVM_ISA_EXT_ARR(SSAIA),
 	KVM_ISA_EXT_ARR(SSCOFPMF),
@@ -112,6 +112,36 @@ static unsigned long kvm_riscv_vcpu_base2isa_ext(unsigned long base_ext)
 	return KVM_RISCV_ISA_EXT_MAX;
 }
 
+static int kvm_riscv_vcpu_isa_check_host(unsigned long kvm_ext, unsigned long *guest_ext)
+{
+	unsigned long host_ext;
+
+	if (kvm_ext >= KVM_RISCV_ISA_EXT_MAX ||
+	    kvm_ext >= ARRAY_SIZE(kvm_isa_ext_arr))
+		return -ENOENT;
+
+	*guest_ext = kvm_isa_ext_arr[kvm_ext];
+	switch (*guest_ext) {
+	case RISCV_ISA_EXT_SMNPM:
+		/*
+		 * Pointer masking effective in (H)S-mode is provided by the
+		 * Smnpm extension, so that extension is reported to the guest,
+		 * even though the CSR bits for configuring VS-mode pointer
+		 * masking on the host side are part of the Ssnpm extension.
+		 */
+		host_ext = RISCV_ISA_EXT_SSNPM;
+		break;
+	default:
+		host_ext = *guest_ext;
+		break;
+	}
+
+	if (!__riscv_isa_extension_available(NULL, host_ext))
+		return -ENOENT;
+
+	return 0;
+}
+
 static bool kvm_riscv_vcpu_isa_enable_allowed(unsigned long ext)
 {
 	switch (ext) {
@@ -219,13 +249,13 @@ static bool kvm_riscv_vcpu_isa_disable_allowed(unsigned long ext)
 
 void kvm_riscv_vcpu_setup_isa(struct kvm_vcpu *vcpu)
 {
-	unsigned long host_isa, i;
+	unsigned long guest_ext, i;
 
 	for (i = 0; i < ARRAY_SIZE(kvm_isa_ext_arr); i++) {
-		host_isa = kvm_isa_ext_arr[i];
-		if (__riscv_isa_extension_available(NULL, host_isa) &&
-		    kvm_riscv_vcpu_isa_enable_allowed(i))
-			set_bit(host_isa, vcpu->arch.isa);
+		if (kvm_riscv_vcpu_isa_check_host(i, &guest_ext))
+			continue;
+		if (kvm_riscv_vcpu_isa_enable_allowed(i))
+			set_bit(guest_ext, vcpu->arch.isa);
 	}
 }
 
@@ -607,18 +637,15 @@ static int riscv_vcpu_get_isa_ext_single(struct kvm_vcpu *vcpu,
 					 unsigned long reg_num,
 					 unsigned long *reg_val)
 {
-	unsigned long host_isa_ext;
-
-	if (reg_num >= KVM_RISCV_ISA_EXT_MAX ||
-	    reg_num >= ARRAY_SIZE(kvm_isa_ext_arr))
-		return -ENOENT;
+	unsigned long guest_ext;
+	int ret;
 
-	host_isa_ext = kvm_isa_ext_arr[reg_num];
-	if (!__riscv_isa_extension_available(NULL, host_isa_ext))
-		return -ENOENT;
+	ret = kvm_riscv_vcpu_isa_check_host(reg_num, &guest_ext);
+	if (ret)
+		return ret;
 
 	*reg_val = 0;
-	if (__riscv_isa_extension_available(vcpu->arch.isa, host_isa_ext))
+	if (__riscv_isa_extension_available(vcpu->arch.isa, guest_ext))
 		*reg_val = 1; /* Mark the given extension as available */
 
 	return 0;
@@ -628,17 +655,14 @@ static int riscv_vcpu_set_isa_ext_single(struct kvm_vcpu *vcpu,
 					 unsigned long reg_num,
 					 unsigned long reg_val)
 {
-	unsigned long host_isa_ext;
-
-	if (reg_num >= KVM_RISCV_ISA_EXT_MAX ||
-	    reg_num >= ARRAY_SIZE(kvm_isa_ext_arr))
-		return -ENOENT;
+	unsigned long guest_ext;
+	int ret;
 
-	host_isa_ext = kvm_isa_ext_arr[reg_num];
-	if (!__riscv_isa_extension_available(NULL, host_isa_ext))
-		return -ENOENT;
+	ret = kvm_riscv_vcpu_isa_check_host(reg_num, &guest_ext);
+	if (ret)
+		return ret;
 
-	if (reg_val == test_bit(host_isa_ext, vcpu->arch.isa))
+	if (reg_val == test_bit(guest_ext, vcpu->arch.isa))
 		return 0;
 
 	if (!vcpu->arch.ran_atleast_once) {
@@ -648,10 +672,10 @@ static int riscv_vcpu_set_isa_ext_single(struct kvm_vcpu *vcpu,
 		 */
 		if (reg_val == 1 &&
 		    kvm_riscv_vcpu_isa_enable_allowed(reg_num))
-			set_bit(host_isa_ext, vcpu->arch.isa);
+			set_bit(guest_ext, vcpu->arch.isa);
 		else if (!reg_val &&
 			 kvm_riscv_vcpu_isa_disable_allowed(reg_num))
-			clear_bit(host_isa_ext, vcpu->arch.isa);
+			clear_bit(guest_ext, vcpu->arch.isa);
 		else
 			return -EINVAL;
 		kvm_riscv_vcpu_fp_reset(vcpu);
@@ -1009,16 +1033,15 @@ static int copy_fp_d_reg_indices(const struct kvm_vcpu *vcpu,
 static int copy_isa_ext_reg_indices(const struct kvm_vcpu *vcpu,
 				u64 __user *uindices)
 {
+	unsigned long guest_ext;
 	unsigned int n = 0;
-	unsigned long isa_ext;
 
 	for (int i = 0; i < KVM_RISCV_ISA_EXT_MAX; i++) {
 		u64 size = IS_ENABLED(CONFIG_32BIT) ?
 			   KVM_REG_SIZE_U32 : KVM_REG_SIZE_U64;
 		u64 reg = KVM_REG_RISCV | size | KVM_REG_RISCV_ISA_EXT | i;
 
-		isa_ext = kvm_isa_ext_arr[i];
-		if (!__riscv_isa_extension_available(NULL, isa_ext))
+		if (kvm_riscv_vcpu_isa_check_host(i, &guest_ext))
 			continue;
 
 		if (uindices) {