linux-kernel - [PATCH hyperv-next 3/6] arch: hyperv: Get/set SynIC synth.registers via paravisor

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Message-ID: <20250409000835.285105-4-romank@linux.microsoft.com>
Date: Tue,  8 Apr 2025 17:08:32 -0700
From: Roman Kisel <romank@...ux.microsoft.com>
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Subject: [PATCH hyperv-next 3/6] arch: hyperv: Get/set SynIC synth.registers via paravisor

The confidential VMBus is built on the guest talking to the
paravisor only.

Provide functions that allow manipulating the SynIC registers
via paravisor.

Signed-off-by: Roman Kisel <romank@...ux.microsoft.com>
---
 arch/arm64/hyperv/mshyperv.c      | 19 +++++++++++++++++++
 arch/arm64/include/asm/mshyperv.h |  3 +++
 arch/x86/include/asm/mshyperv.h   |  3 +++
 arch/x86/kernel/cpu/mshyperv.c    | 28 ++++++++++++++++++++++++++++
 4 files changed, 53 insertions(+)

diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
index 4e27cc29c79e..1647a57a3379 100644
--- a/arch/arm64/hyperv/mshyperv.c
+++ b/arch/arm64/hyperv/mshyperv.c
@@ -91,3 +91,22 @@ bool hv_is_hyperv_initialized(void)
 	return hyperv_initialized;
 }
 EXPORT_SYMBOL_GPL(hv_is_hyperv_initialized);
+
+/*
+ * Not supported yet.
+ */
+u64 hv_pv_get_synic_register(unsigned int reg, int *err)
+{
+	*err = -ENODEV;
+	return !0ULL;
+}
+EXPORT_SYMBOL_GPL(hv_pv_get_synic_register);
+
+/*
+ * Not supported yet.
+ */
+int hv_pv_set_synic_register(unsigned int reg, u64 val)
+{
+	return -ENODEV;
+}
+EXPORT_SYMBOL_GPL(hv_pv_set_synic_register);
diff --git a/arch/arm64/include/asm/mshyperv.h b/arch/arm64/include/asm/mshyperv.h
index b721d3134ab6..bce37a58dff0 100644
--- a/arch/arm64/include/asm/mshyperv.h
+++ b/arch/arm64/include/asm/mshyperv.h
@@ -53,6 +53,9 @@ static inline u64 hv_get_non_nested_msr(unsigned int reg)
 	return hv_get_msr(reg);
 }
 
+u64 hv_pv_get_synic_register(unsigned int reg, int *err);
+int hv_pv_set_synic_register(unsigned int reg, u64 val);
+
 /* SMCCC hypercall parameters */
 #define HV_SMCCC_FUNC_NUMBER	1
 #define HV_FUNC_ID	ARM_SMCCC_CALL_VAL(			\
diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index 07aadf0e839f..5650a16cc5e8 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -307,6 +307,9 @@ static __always_inline u64 hv_raw_get_msr(unsigned int reg)
 	return __rdmsr(reg);
 }
 
+u64 hv_pv_get_synic_register(unsigned int reg, int *err);
+int hv_pv_set_synic_register(unsigned int reg, u64 val);
+
 #else /* CONFIG_HYPERV */
 static inline void hyperv_init(void) {}
 static inline void hyperv_setup_mmu_ops(void) {}
diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 3e2533954675..4f6e3d02f730 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -89,6 +89,34 @@ void hv_set_non_nested_msr(unsigned int reg, u64 value)
 }
 EXPORT_SYMBOL_GPL(hv_set_non_nested_msr);
 
+/*
+ * Not every paravisor supports getting SynIC registers, and
+ * this function may fail. The caller has to make sure that this function
+ * runs on the CPU of interest.
+ */
+u64 hv_pv_get_synic_register(unsigned int reg, int *err)
+{
+	if (!hv_is_synic_msr(reg)) {
+		*err = -ENODEV;
+		return !0ULL;
+	}
+	return native_read_msr_safe(reg, err);
+}
+EXPORT_SYMBOL_GPL(hv_pv_get_synic_register);
+
+/*
+ * Not every paravisor supports setting SynIC registers, and
+ * this function may fail. The caller has to make sure that this function
+ * runs on the CPU of interest.
+ */
+int hv_pv_set_synic_register(unsigned int reg, u64 val)
+{
+	if (!hv_is_synic_msr(reg))
+		return -ENODEV;
+	return wrmsrl_safe(reg, val);
+}
+EXPORT_SYMBOL_GPL(hv_pv_set_synic_register);
+
 u64 hv_get_msr(unsigned int reg)
 {
 	if (hv_nested)
-- 
2.43.0