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

We will be optimizing HSTATUS CSR access via shared memory setup
using the SBI nested acceleration extension. To facilitate this,
we first move HSTATUS save/restore in kvm_riscv_vcpu_enter_exit().

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Link: https://lore.kernel.org/r/20241020194734.58686-3-apatel@ventanamicro.com
Signed-off-by: Anup Patel <anup@brainfault.org>

Author: avpatel

arch/riscv/kvm/vcpu.c

@@ -727,9 +727,18 @@ static __always_inline void kvm_riscv_vcpu_swap_in_host_state(struct kvm_vcpu *v
  */
 static void noinstr kvm_riscv_vcpu_enter_exit(struct kvm_vcpu *vcpu)
 {
+	struct kvm_cpu_context *gcntx = &vcpu->arch.guest_context;
+	struct kvm_cpu_context *hcntx = &vcpu->arch.host_context;
+
 	kvm_riscv_vcpu_swap_in_guest_state(vcpu);
 	guest_state_enter_irqoff();
+
+	hcntx->hstatus = csr_swap(CSR_HSTATUS, gcntx->hstatus);
+
 	__kvm_riscv_switch_to(&vcpu->arch);
+
+	gcntx->hstatus = csr_swap(CSR_HSTATUS, hcntx->hstatus);
+
 	vcpu->arch.last_exit_cpu = vcpu->cpu;
 	guest_state_exit_irqoff();
 	kvm_riscv_vcpu_swap_in_host_state(vcpu);

arch/riscv/kvm/vcpu_switch.S

@@ -43,35 +43,30 @@ 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_HSTATUS)(a0)
-	REG_L	t2, (KVM_ARCH_GUEST_SCOUNTEREN)(a0)
-	la	t4, .Lkvm_switch_return
-	REG_L	t5, (KVM_ARCH_GUEST_SEPC)(a0)
+	REG_L	t1, (KVM_ARCH_GUEST_SCOUNTEREN)(a0)
+	la	t3, .Lkvm_switch_return
+	REG_L	t4, (KVM_ARCH_GUEST_SEPC)(a0)
 
 	/* Save Host and Restore Guest SSTATUS */
 	csrrw	t0, CSR_SSTATUS, t0
 
-	/* Save Host and Restore Guest HSTATUS */
-	csrrw	t1, CSR_HSTATUS, t1
-
 	/* Save Host and Restore Guest SCOUNTEREN */
-	csrrw	t2, CSR_SCOUNTEREN, t2
+	csrrw	t1, CSR_SCOUNTEREN, t1
 
 	/* Save Host STVEC and change it to return path */
-	csrrw	t4, CSR_STVEC, t4
+	csrrw	t3, CSR_STVEC, t3
 
 	/* Save Host SSCRATCH and change it to struct kvm_vcpu_arch pointer */
-	csrrw	t3, CSR_SSCRATCH, a0
+	csrrw	t2, CSR_SSCRATCH, a0
 
 	/* Restore Guest SEPC */
-	csrw	CSR_SEPC, t5
+	csrw	CSR_SEPC, t4
 
 	/* Store Host CSR values */
 	REG_S	t0, (KVM_ARCH_HOST_SSTATUS)(a0)
-	REG_S	t1, (KVM_ARCH_HOST_HSTATUS)(a0)
-	REG_S	t2, (KVM_ARCH_HOST_SCOUNTEREN)(a0)
-	REG_S	t3, (KVM_ARCH_HOST_SSCRATCH)(a0)
-	REG_S	t4, (KVM_ARCH_HOST_STVEC)(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)
 
 	/* Restore Guest GPRs (except A0) */
 	REG_L	ra, (KVM_ARCH_GUEST_RA)(a0)
@@ -153,8 +148,7 @@ SYM_FUNC_START(__kvm_riscv_switch_to)
 	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_HSTATUS)(a0)
-	REG_L	t5, (KVM_ARCH_HOST_SSTATUS)(a0)
+	REG_L	t4, (KVM_ARCH_HOST_SSTATUS)(a0)
 
 	/* Save Guest SEPC */
 	csrr	t0, CSR_SEPC
@@ -168,18 +162,14 @@ SYM_FUNC_START(__kvm_riscv_switch_to)
 	/* Save Guest and Restore Host SCOUNTEREN */
 	csrrw	t3, CSR_SCOUNTEREN, t3
 
-	/* Save Guest and Restore Host HSTATUS */
-	csrrw	t4, CSR_HSTATUS, t4
-
 	/* Save Guest and Restore Host SSTATUS */
-	csrrw	t5, CSR_SSTATUS, t5
+	csrrw	t4, CSR_SSTATUS, t4
 
 	/* 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_HSTATUS)(a0)
-	REG_S	t5, (KVM_ARCH_GUEST_SSTATUS)(a0)
+	REG_S	t4, (KVM_ARCH_GUEST_SSTATUS)(a0)
 
 	/* Restore Host GPRs (except A0 and T0-T6) */
 	REG_L	ra, (KVM_ARCH_HOST_RA)(a0)