[RFC PATCH 10/14] RISC-V: KVM: Add support for SBI STA registers

[Andrew Jones]

KVM userspace needs to be able to save and restore the steal-time
shared memory address. Provide the address through the get/set-one-reg
interface with two ulong-sized SBI STA extension registers (lo and hi).
64-bit KVM will always save/restore zero for the hi register.

Signed-off-by: Andrew Jones <ajones at ventanamicro.com>
---
 arch/riscv/include/asm/kvm_vcpu_sbi.h |  4 +++
 arch/riscv/include/uapi/asm/kvm.h     | 10 ++++++
 arch/riscv/kvm/vcpu.c                 |  5 +++
 arch/riscv/kvm/vcpu_sbi_sta.c         | 52 +++++++++++++++++++++++++++
 4 files changed, 71 insertions(+)

diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi.h b/arch/riscv/include/asm/kvm_vcpu_sbi.h
index c63c6bbc2f74..ed5a294c479a 100644
--- a/arch/riscv/include/asm/kvm_vcpu_sbi.h
+++ b/arch/riscv/include/asm/kvm_vcpu_sbi.h
@@ -52,6 +52,10 @@ int kvm_riscv_vcpu_get_reg_sbi_ext(struct kvm_vcpu *vcpu,
 				   const struct kvm_one_reg *reg);
 const struct kvm_vcpu_sbi_extension *kvm_vcpu_sbi_find_ext(
 				struct kvm_vcpu *vcpu, unsigned long extid);
+int kvm_riscv_vcpu_get_reg_sbi_sta(struct kvm_vcpu *vcpu, unsigned long reg_num,
+				   unsigned long *reg_val);
+int kvm_riscv_vcpu_set_reg_sbi_sta(struct kvm_vcpu *vcpu, unsigned long reg_num,
+				   unsigned long reg_val);
 int kvm_riscv_vcpu_sbi_ecall(struct kvm_vcpu *vcpu, struct kvm_run *run);
 
 #ifdef CONFIG_RISCV_SBI_V01
diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
index 172dc565e01a..17b109a9ba7b 100644
--- a/arch/riscv/include/uapi/asm/kvm.h
+++ b/arch/riscv/include/uapi/asm/kvm.h
@@ -128,6 +128,12 @@ enum KVM_RISCV_SBI_EXT_ID {
 	KVM_RISCV_SBI_EXT_MAX,
 };
 
+/* SBI STA extension registers for KVM_GET_ONE_REG and KVM_SET_ONE_REG */
+struct kvm_riscv_sbi_sta {
+	unsigned long shmem_lo;
+	unsigned long shmem_hi;
+};
+
 /* Possible states for kvm_riscv_timer */
 #define KVM_RISCV_TIMER_STATE_OFF	0
 #define KVM_RISCV_TIMER_STATE_ON	1
@@ -189,6 +195,10 @@ enum KVM_RISCV_SBI_EXT_ID {
 /* Registers for specific SBI extensions are mapped as type 9 */
 #define KVM_REG_RISCV_SBI		(0x09 << KVM_REG_RISCV_TYPE_SHIFT)
 
+#define KVM_REG_RISCV_SBI_STA		(0x1 << KVM_REG_RISCV_SUBTYPE_SHIFT)
+#define KVM_REG_RISCV_SBI_STA_REG(name)	\
+	(offsetof(struct kvm_riscv_sbi_sta, name) / sizeof(unsigned long))
+
 #endif
 
 #endif /* __LINUX_KVM_RISCV_H */
diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
index 56aec4c2521e..bdc14ebf50a3 100644
--- a/arch/riscv/kvm/vcpu.c
+++ b/arch/riscv/kvm/vcpu.c
@@ -603,6 +603,9 @@ static int kvm_riscv_vcpu_get_reg_sbi(struct kvm_vcpu *vcpu,
 	reg_num &= ~KVM_REG_RISCV_SUBTYPE_MASK;
 
 	switch (reg_subtype) {
+	case KVM_REG_RISCV_SBI_STA:
+		ret = kvm_riscv_vcpu_get_reg_sbi_sta(vcpu, reg_num, &reg_val);
+		break;
 	default:
 		return -EINVAL;
 	}
@@ -636,6 +639,8 @@ static int kvm_riscv_vcpu_set_reg_sbi(struct kvm_vcpu *vcpu,
 	reg_num &= ~KVM_REG_RISCV_SUBTYPE_MASK;
 
 	switch (reg_subtype) {
+	case KVM_REG_RISCV_SBI_STA:
+		return kvm_riscv_vcpu_set_reg_sbi_sta(vcpu, reg_num, reg_val);
 	default:
 		return -EINVAL;
 	}
diff --git a/arch/riscv/kvm/vcpu_sbi_sta.c b/arch/riscv/kvm/vcpu_sbi_sta.c
index bc4f7390a9a8..3d98f140bd06 100644
--- a/arch/riscv/kvm/vcpu_sbi_sta.c
+++ b/arch/riscv/kvm/vcpu_sbi_sta.c
@@ -3,6 +3,7 @@
  * Copyright (c) 2023 Ventana Micro Systems Inc.
  */
 
+#include <linux/kconfig.h>
 #include <linux/kernel.h>
 #include <linux/kvm_host.h>
 #include <linux/mm.h>
@@ -145,3 +146,54 @@ const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_sta = {
 	.handler = kvm_sbi_ext_sta_handler,
 	.probe = kvm_sbi_ext_sta_probe,
 };
+
+int kvm_riscv_vcpu_get_reg_sbi_sta(struct kvm_vcpu *vcpu,
+				   unsigned long reg_num,
+				   unsigned long *reg_val)
+{
+	switch (reg_num) {
+	case KVM_REG_RISCV_SBI_STA_REG(shmem_lo):
+		*reg_val = (unsigned long)vcpu->arch.sta.shmem;
+		break;
+	case KVM_REG_RISCV_SBI_STA_REG(shmem_hi):
+		if (IS_ENABLED(CONFIG_32BIT))
+			*reg_val = upper_32_bits(vcpu->arch.sta.shmem);
+		else
+			*reg_val = 0;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+int kvm_riscv_vcpu_set_reg_sbi_sta(struct kvm_vcpu *vcpu,
+				   unsigned long reg_num,
+				   unsigned long reg_val)
+{
+	switch (reg_num) {
+	case KVM_REG_RISCV_SBI_STA_REG(shmem_lo):
+		if (IS_ENABLED(CONFIG_32BIT)) {
+			gpa_t hi = upper_32_bits(vcpu->arch.sta.shmem);
+
+			vcpu->arch.sta.shmem = reg_val;
+			vcpu->arch.sta.shmem |= hi << 32;
+		} else
+			vcpu->arch.sta.shmem = reg_val;
+		break;
+	case KVM_REG_RISCV_SBI_STA_REG(shmem_hi):
+		if (IS_ENABLED(CONFIG_32BIT)) {
+			gpa_t lo = lower_32_bits(vcpu->arch.sta.shmem);
+
+			vcpu->arch.sta.shmem = ((gpa_t)reg_val << 32);
+			vcpu->arch.sta.shmem |= lo;
+		} else if (reg_val != 0)
+			return -EINVAL;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
-- 
2.39.2