[PATCH 12/16] riscv: kvm: Add emulated test csr

[Charlie Jenkins via B4 Relay]

From: Charlie Jenkins <thecharlesjenkins at gmail.com>

To test the riscv kvm implementation of emulated CSRs, add support to
emulate the vsscratch csr when CONFIG_RISCV_KVM_TEST_CSR is set.

Signed-off-by: Charlie Jenkins <thecharlesjenkins at gmail.com>
---
 arch/riscv/Kconfig.debug                   |  1 +
 arch/riscv/include/asm/kvm_host.h          | 10 ++++++++++
 arch/riscv/include/asm/kvm_vcpu_test_csr.h | 15 +++++++++++++++
 arch/riscv/kvm/Kconfig.debug               | 16 ++++++++++++++++
 arch/riscv/kvm/Makefile                    |  1 +
 arch/riscv/kvm/vcpu_insn.c                 |  5 +++++
 arch/riscv/kvm/vcpu_test_csr.c             | 21 +++++++++++++++++++++
 7 files changed, 69 insertions(+)

diff --git a/arch/riscv/Kconfig.debug b/arch/riscv/Kconfig.debug
index eafe17ebf710..be202267da6d 100644
--- a/arch/riscv/Kconfig.debug
+++ b/arch/riscv/Kconfig.debug
@@ -1 +1,2 @@
 source "arch/riscv/kernel/tests/Kconfig.debug"
+source "arch/riscv/kvm/Kconfig.debug"
diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
index 24585304c02b..709a1c18ce22 100644
--- a/arch/riscv/include/asm/kvm_host.h
+++ b/arch/riscv/include/asm/kvm_host.h
@@ -183,6 +183,12 @@ struct kvm_vcpu_reset_state {
 	unsigned long a1;
 };
 
+#ifdef CONFIG_RISCV_KVM_TEST_CSR
+struct kvm_test_csr {
+	unsigned long val;
+};
+#endif
+
 struct kvm_vcpu_arch {
 	/* VCPU ran at least once */
 	bool ran_atleast_once;
@@ -278,6 +284,10 @@ struct kvm_vcpu_arch {
 		gpa_t shmem;
 		u64 last_steal;
 	} sta;
+
+#ifdef CONFIG_RISCV_KVM_TEST_CSR
+	struct kvm_test_csr test_csr;
+#endif
 };
 
 /*
diff --git a/arch/riscv/include/asm/kvm_vcpu_test_csr.h b/arch/riscv/include/asm/kvm_vcpu_test_csr.h
new file mode 100644
index 000000000000..a844fccaafc3
--- /dev/null
+++ b/arch/riscv/include/asm/kvm_vcpu_test_csr.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef __KVM_VCPU_RISCV_TEST_CSR_H
+#define __KVM_VCPU_RISCV_TEST_CSR_H
+
+#include <asm/kvm_vcpu_insn.h>
+
+#define KVM_RISCV_VCPU_TEST_CSR_FUNCS \
+	{.base = CSR_VSSCRATCH,	.count = 1,	.func = kvm_riscv_vcpu_test_csr },
+
+int kvm_riscv_vcpu_test_csr(struct kvm_vcpu *vcpu, unsigned int csr_num,
+			    unsigned long *val, unsigned long new_val,
+			    unsigned long wr_mask);
+
+#endif /* !__KVM_VCPU_RISCV_TEST_CSR_H */
diff --git a/arch/riscv/kvm/Kconfig.debug b/arch/riscv/kvm/Kconfig.debug
new file mode 100644
index 000000000000..dc76e02120a3
--- /dev/null
+++ b/arch/riscv/kvm/Kconfig.debug
@@ -0,0 +1,16 @@
+# SPDX-License-Identifier: GPL-2.0-only
+menu "arch/riscv/kvm testing"
+
+config RISCV_KVM_TEST_CSR
+        bool "Test KVM CSR emulation"
+        depends on KVM
+        default n
+        help
+            Enable this option to enable the emulation of a test hypervisor csr.
+            The KVM test csr is the vsscratch register. Once this is enabled,
+            reading/writing to the vsscratch register will trap into the host
+            supervisor and reflect the change.
+
+            If unsure, say N.
+
+endmenu # "arch/riscv/kvm testing"
diff --git a/arch/riscv/kvm/Makefile b/arch/riscv/kvm/Makefile
index 3b8afb038b35..02fd27ff33eb 100644
--- a/arch/riscv/kvm/Makefile
+++ b/arch/riscv/kvm/Makefile
@@ -36,6 +36,7 @@ kvm-y += vcpu_sbi_sta.o
 kvm-y += vcpu_sbi_system.o
 kvm-$(CONFIG_RISCV_SBI_V01) += vcpu_sbi_v01.o
 kvm-y += vcpu_switch.o
+kvm-$(CONFIG_RISCV_KVM_TEST_CSR) += vcpu_test_csr.o
 kvm-y += vcpu_timer.o
 kvm-y += vcpu_vector.o
 kvm-y += vm.o
diff --git a/arch/riscv/kvm/vcpu_insn.c b/arch/riscv/kvm/vcpu_insn.c
index 1d8741d02242..c5a70de4a579 100644
--- a/arch/riscv/kvm/vcpu_insn.c
+++ b/arch/riscv/kvm/vcpu_insn.c
@@ -10,6 +10,8 @@
 #include <asm/cpufeature.h>
 #include <asm/insn.h>
 
+#include <asm/kvm_vcpu_test_csr.h>
+
 struct insn_func {
 	unsigned long mask;
 	unsigned long match;
@@ -112,6 +114,9 @@ static int seed_csr_rmw(struct kvm_vcpu *vcpu, unsigned int csr_num,
 static const struct csr_func csr_funcs[] = {
 	KVM_RISCV_VCPU_AIA_CSR_FUNCS
 	KVM_RISCV_VCPU_HPMCOUNTER_CSR_FUNCS
+#ifdef CONFIG_RISCV_KVM_TEST_CSR
+	KVM_RISCV_VCPU_TEST_CSR_FUNCS
+#endif
 	{ .base = CSR_SEED, .count = 1, .func = seed_csr_rmw },
 };
 
diff --git a/arch/riscv/kvm/vcpu_test_csr.c b/arch/riscv/kvm/vcpu_test_csr.c
new file mode 100644
index 000000000000..b8aa503cdaba
--- /dev/null
+++ b/arch/riscv/kvm/vcpu_test_csr.c
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/kvm_host.h>
+#include <asm/kvm_vcpu_insn.h>
+#include <asm/kvm_vcpu_test_csr.h>
+
+#define vcpu_to_test_csr(vcpu) (&(vcpu)->arch.test_csr)
+
+int kvm_riscv_vcpu_test_csr(struct kvm_vcpu *vcpu, unsigned int csr_num,
+			    unsigned long *val, unsigned long new_val,
+			    unsigned long wr_mask)
+{
+	struct kvm_test_csr *test_csr = vcpu_to_test_csr(vcpu);
+
+	*val = test_csr->val;
+
+	if (wr_mask)
+		test_csr->val = (test_csr->val & ~wr_mask) | (new_val & wr_mask);
+
+	return KVM_INSN_CONTINUE_NEXT_SEPC;
+}

-- 
2.52.0