[RFC PATCH 5/6] RISC-V: KVM: Introduce ISA extension register

[Atish Patra]

Currently, there is no provision for vmm (qemu-kvm or kvmtool) to
query about multiple-letter ISA extensions. The config register
is only used for base single letter ISA extensions.

A new ISA extension register is added that will allow the vmm
to query about any ISA extension one at a time. It is enabled for
both single letter or multi-letter ISA extensions. The ISA extension
register is useful to if the vmm requires to retrieve/set single
extension while the config register should be used if all the base
ISA extension required to retrieve or set.

For any multi-letter ISA extensions, the new register interface
must be used.

Signed-off-by: Atish Patra <atishp at rivosinc.com>
---
 arch/riscv/include/uapi/asm/kvm.h |  20 ++++++
 arch/riscv/kvm/vcpu.c             | 101 ++++++++++++++++++++++++++++++
 2 files changed, 121 insertions(+)

diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
index aa9f5a5c57d8..e01678aa2a55 100644
--- a/arch/riscv/include/uapi/asm/kvm.h
+++ b/arch/riscv/include/uapi/asm/kvm.h
@@ -83,6 +83,23 @@ struct kvm_riscv_timer {
 	__u64 state;
 };
 
+/**
+ * ISA extension IDs specific to KVM. This is not the same as the host ISA
+ * extension IDs as that is internal to the host and should not be exposed
+ * to the guest. This should always be contiguous to keep the mapping simple
+ * in KVM implementation.
+ */
+enum KVM_RISCV_ISA_EXT_ID {
+	KVM_RISCV_ISA_EXT_A = 0,
+	KVM_RISCV_ISA_EXT_C,
+	KVM_RISCV_ISA_EXT_D,
+	KVM_RISCV_ISA_EXT_F,
+	KVM_RISCV_ISA_EXT_H,
+	KVM_RISCV_ISA_EXT_I,
+	KVM_RISCV_ISA_EXT_M,
+	KVM_RISCV_ISA_EXT_MAX,
+};
+
 /* Possible states for kvm_riscv_timer */
 #define KVM_RISCV_TIMER_STATE_OFF	0
 #define KVM_RISCV_TIMER_STATE_ON	1
@@ -124,6 +141,9 @@ struct kvm_riscv_timer {
 #define KVM_REG_RISCV_FP_D_REG(name)	\
 		(offsetof(struct __riscv_d_ext_state, name) / sizeof(__u64))
 
+/* ISA Extension registers are mapped as type 7 */
+#define KVM_REG_RISCV_ISA_EXT		(0x07 << KVM_REG_RISCV_TYPE_SHIFT)
+
 #endif
 
 #endif /* __LINUX_KVM_RISCV_H */
diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
index 7a07dba504f8..c314c40be313 100644
--- a/arch/riscv/kvm/vcpu.c
+++ b/arch/riscv/kvm/vcpu.c
@@ -364,6 +364,103 @@ static int kvm_riscv_vcpu_set_reg_csr(struct kvm_vcpu *vcpu,
 	return 0;
 }
 
+/* Mapping between KVM ISA Extension ID & Host ISA extension ID */
+static unsigned long kvm_isa_ext_arr[] = {
+	RISCV_ISA_EXT_a,
+	RISCV_ISA_EXT_c,
+	RISCV_ISA_EXT_d,
+	RISCV_ISA_EXT_f,
+	RISCV_ISA_EXT_h,
+	RISCV_ISA_EXT_i,
+	RISCV_ISA_EXT_m,
+};
+
+static int kvm_riscv_vcpu_get_reg_isa_ext(struct kvm_vcpu *vcpu,
+					  const struct kvm_one_reg *reg)
+{
+	unsigned long __user *uaddr =
+			(unsigned long __user *)(unsigned long)reg->addr;
+	unsigned long reg_num = reg->id & ~(KVM_REG_ARCH_MASK |
+					    KVM_REG_SIZE_MASK |
+					    KVM_REG_RISCV_ISA_EXT);
+	unsigned long reg_val = 0;
+	unsigned long host_isa_ext;
+
+	if (KVM_REG_SIZE(reg->id) != sizeof(unsigned long))
+		return -EINVAL;
+
+	if (reg_num >= KVM_RISCV_ISA_EXT_MAX || reg_num >= ARRAY_SIZE(kvm_isa_ext_arr))
+		return -EINVAL;
+
+	host_isa_ext = kvm_isa_ext_arr[reg_num];
+	if (__riscv_isa_extension_available(NULL, host_isa_ext))
+		reg_val = 1; /* Mark the given extension as available */
+
+	if (copy_to_user(uaddr, &reg_val, KVM_REG_SIZE(reg->id)))
+		return -EFAULT;
+
+	return 0;
+}
+
+static int kvm_riscv_vcpu_set_reg_isa_ext(struct kvm_vcpu *vcpu,
+					  const struct kvm_one_reg *reg)
+{
+	unsigned long __user *uaddr =
+			(unsigned long __user *)(unsigned long)reg->addr;
+	unsigned long reg_num = reg->id & ~(KVM_REG_ARCH_MASK |
+					    KVM_REG_SIZE_MASK |
+					    KVM_REG_RISCV_ISA_EXT);
+	unsigned long reg_val;
+	unsigned long host_isa_ext;
+	unsigned long host_isa_ext_mask;
+
+	if (KVM_REG_SIZE(reg->id) != sizeof(unsigned long))
+		return -EINVAL;
+
+	if (KVM_REG_SIZE(reg->id) != sizeof(unsigned long))
+		return -EINVAL;
+
+	if (reg_num >= KVM_RISCV_ISA_EXT_MAX || reg_num >= ARRAY_SIZE(kvm_isa_ext_arr))
+		return -EINVAL;
+
+	if (copy_from_user(&reg_val, uaddr, KVM_REG_SIZE(reg->id)))
+		return -EFAULT;
+
+	host_isa_ext = kvm_isa_ext_arr[reg_num];
+	if (!__riscv_isa_extension_available(NULL, host_isa_ext))
+		return	-EOPNOTSUPP;
+
+	if (host_isa_ext >= RISCV_ISA_EXT_BASE &&
+	    host_isa_ext < RISCV_ISA_EXT_MAX) {
+		/** Multi-letter ISA extension. Currently there is no provision
+		 * to enable/disable the multi-letter ISA extensions for guests.
+		 * Return success if the request is to enable any ISA extension
+		 * that is available in the hardware.
+		 * Return -EOPNOTSUPP otherwise.
+		 */
+		if (!reg_val)
+			return -EOPNOTSUPP;
+		else
+			return 0;
+	}
+
+	/* Single letter base ISA extension */
+	if (!vcpu->arch.ran_atleast_once) {
+		host_isa_ext_mask = reg_val ? (1 << host_isa_ext) : ~(1 << host_isa_ext);
+		if (!reg_val)
+			vcpu->arch.isa &= host_isa_ext_mask;
+		else
+			vcpu->arch.isa |= host_isa_ext_mask;
+		vcpu->arch.isa &= riscv_isa_extension_base(NULL);
+		vcpu->arch.isa &= KVM_RISCV_ISA_ALLOWED;
+		kvm_riscv_vcpu_fp_reset(vcpu);
+	} else {
+		return -EOPNOTSUPP;
+	}
+
+	return 0;
+}
+
 static int kvm_riscv_vcpu_set_reg(struct kvm_vcpu *vcpu,
 				  const struct kvm_one_reg *reg)
 {
@@ -381,6 +478,8 @@ static int kvm_riscv_vcpu_set_reg(struct kvm_vcpu *vcpu,
 	else if ((reg->id & KVM_REG_RISCV_TYPE_MASK) == KVM_REG_RISCV_FP_D)
 		return kvm_riscv_vcpu_set_reg_fp(vcpu, reg,
 						 KVM_REG_RISCV_FP_D);
+	else if ((reg->id & KVM_REG_RISCV_TYPE_MASK) == KVM_REG_RISCV_ISA_EXT)
+		return kvm_riscv_vcpu_set_reg_isa_ext(vcpu, reg);
 
 	return -EINVAL;
 }
@@ -402,6 +501,8 @@ static int kvm_riscv_vcpu_get_reg(struct kvm_vcpu *vcpu,
 	else if ((reg->id & KVM_REG_RISCV_TYPE_MASK) == KVM_REG_RISCV_FP_D)
 		return kvm_riscv_vcpu_get_reg_fp(vcpu, reg,
 						 KVM_REG_RISCV_FP_D);
+	else if ((reg->id & KVM_REG_RISCV_TYPE_MASK) == KVM_REG_RISCV_ISA_EXT)
+		return kvm_riscv_vcpu_get_reg_isa_ext(vcpu, reg);
 
 	return -EINVAL;
 }
-- 
2.30.2