RISC-V: KVM: Save/restore SCOUNTEREN in C source

The SCOUNTEREN CSR need not be saved/restored in the low-level
__kvm_riscv_switch_to() function hence move the SCOUNTEREN CSR
save/restore to the kvm_riscv_vcpu_swap_in_guest_state() and
kvm_riscv_vcpu_swap_in_host_state() functions in C sources.

Also, re-arrange the CSR save/restore and related GPR usage in
the low-level __kvm_riscv_switch_to() low-level function.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Link: https://lore.kernel.org/r/20241020194734.58686-4-apatel@ventanamicro.com
Signed-off-by: Anup Patel <anup@brainfault.org>

2 files changed, 23 insertions, 31 deletions

diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
index c9933ea170f4..05ccb3b97bab 100644
--- a/arch/riscv/kvm/vcpu.c
+++ b/arch/riscv/kvm/vcpu.c
@@ -698,6 +698,7 @@ static __always_inline void kvm_riscv_vcpu_swap_in_guest_state(struct kvm_vcpu *
 	struct kvm_vcpu_csr *csr = &vcpu->arch.guest_csr;
 	struct kvm_vcpu_config *cfg = &vcpu->arch.cfg;
 
+	vcpu->arch.host_scounteren = csr_swap(CSR_SCOUNTEREN, csr->scounteren);
 	vcpu->arch.host_senvcfg = csr_swap(CSR_SENVCFG, csr->senvcfg);
 	if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SMSTATEEN) &&
 	    (cfg->hstateen0 & SMSTATEEN0_SSTATEEN0))
@@ -711,6 +712,7 @@ static __always_inline void kvm_riscv_vcpu_swap_in_host_state(struct kvm_vcpu *v
 	struct kvm_vcpu_csr *csr = &vcpu->arch.guest_csr;
 	struct kvm_vcpu_config *cfg = &vcpu->arch.cfg;
 
+	csr->scounteren = csr_swap(CSR_SCOUNTEREN, vcpu->arch.host_scounteren);
 	csr->senvcfg = csr_swap(CSR_SENVCFG, vcpu->arch.host_senvcfg);
 	if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SMSTATEEN) &&
 	    (cfg->hstateen0 & SMSTATEEN0_SSTATEEN0))
diff --git a/arch/riscv/kvm/vcpu_switch.S b/arch/riscv/kvm/vcpu_switch.S
index f83643c4fdb9..3f8cbc21a644 100644
--- a/arch/riscv/kvm/vcpu_switch.S
+++ b/arch/riscv/kvm/vcpu_switch.S
@@ -43,30 +43,25 @@ SYM_FUNC_START(__kvm_riscv_switch_to)
 
 	/* Load Guest CSR values */
 	REG_L	t0, (KVM_ARCH_GUEST_SSTATUS)(a0)
-	REG_L	t1, (KVM_ARCH_GUEST_SCOUNTEREN)(a0)
-	la	t3, .Lkvm_switch_return
-	REG_L	t4, (KVM_ARCH_GUEST_SEPC)(a0)
+	la	t1, .Lkvm_switch_return
+	REG_L	t2, (KVM_ARCH_GUEST_SEPC)(a0)
 
 	/* Save Host and Restore Guest SSTATUS */
 	csrrw	t0, CSR_SSTATUS, t0
 
-	/* Save Host and Restore Guest SCOUNTEREN */
-	csrrw	t1, CSR_SCOUNTEREN, t1
-
 	/* Save Host STVEC and change it to return path */
-	csrrw	t3, CSR_STVEC, t3
-
-	/* Save Host SSCRATCH and change it to struct kvm_vcpu_arch pointer */
-	csrrw	t2, CSR_SSCRATCH, a0
+	csrrw	t1, CSR_STVEC, t1
 
 	/* Restore Guest SEPC */
-	csrw	CSR_SEPC, t4
+	csrw	CSR_SEPC, t2
+
+	/* Save Host SSCRATCH and change it to struct kvm_vcpu_arch pointer */
+	csrrw	t3, CSR_SSCRATCH, a0
 
 	/* Store Host CSR values */
 	REG_S	t0, (KVM_ARCH_HOST_SSTATUS)(a0)
-	REG_S	t1, (KVM_ARCH_HOST_SCOUNTEREN)(a0)
-	REG_S	t2, (KVM_ARCH_HOST_SSCRATCH)(a0)
-	REG_S	t3, (KVM_ARCH_HOST_STVEC)(a0)
+	REG_S	t1, (KVM_ARCH_HOST_STVEC)(a0)
+	REG_S	t3, (KVM_ARCH_HOST_SSCRATCH)(a0)
 
 	/* Restore Guest GPRs (except A0) */
 	REG_L	ra, (KVM_ARCH_GUEST_RA)(a0)
@@ -145,31 +140,26 @@ SYM_FUNC_START(__kvm_riscv_switch_to)
 	REG_S	t6, (KVM_ARCH_GUEST_T6)(a0)
 
 	/* Load Host CSR values */
-	REG_L	t1, (KVM_ARCH_HOST_STVEC)(a0)
-	REG_L	t2, (KVM_ARCH_HOST_SSCRATCH)(a0)
-	REG_L	t3, (KVM_ARCH_HOST_SCOUNTEREN)(a0)
-	REG_L	t4, (KVM_ARCH_HOST_SSTATUS)(a0)
-
-	/* Save Guest SEPC */
-	csrr	t0, CSR_SEPC
+	REG_L	t0, (KVM_ARCH_HOST_STVEC)(a0)
+	REG_L	t1, (KVM_ARCH_HOST_SSCRATCH)(a0)
+	REG_L	t2, (KVM_ARCH_HOST_SSTATUS)(a0)
 
 	/* Save Guest A0 and Restore Host SSCRATCH */
-	csrrw	t2, CSR_SSCRATCH, t2
+	csrrw	t1, CSR_SSCRATCH, t1
 
-	/* Restore Host STVEC */
-	csrw	CSR_STVEC, t1
+	/* Save Guest SEPC */
+	csrr	t3, CSR_SEPC
 
-	/* Save Guest and Restore Host SCOUNTEREN */
-	csrrw	t3, CSR_SCOUNTEREN, t3
+	/* Restore Host STVEC */
+	csrw	CSR_STVEC, t0
 
 	/* Save Guest and Restore Host SSTATUS */
-	csrrw	t4, CSR_SSTATUS, t4
+	csrrw	t2, CSR_SSTATUS, t2
 
 	/* Store Guest CSR values */
-	REG_S	t0, (KVM_ARCH_GUEST_SEPC)(a0)
-	REG_S	t2, (KVM_ARCH_GUEST_A0)(a0)
-	REG_S	t3, (KVM_ARCH_GUEST_SCOUNTEREN)(a0)
-	REG_S	t4, (KVM_ARCH_GUEST_SSTATUS)(a0)
+	REG_S	t1, (KVM_ARCH_GUEST_A0)(a0)
+	REG_S	t2, (KVM_ARCH_GUEST_SSTATUS)(a0)
+	REG_S	t3, (KVM_ARCH_GUEST_SEPC)(a0)
 
 	/* Restore Host GPRs (except A0 and T0-T6) */
 	REG_L	ra, (KVM_ARCH_HOST_RA)(a0)