On 4/27/2026 11:08 AM, Michael Kelley wrote:
From: Naman Jain <[email protected]> Sent: Thursday, April 23, 2026
5:42 AM
Add the arm64 variant of mshv_vtl_return_call() to support the MSHV_VTL
driver on arm64. This function enables the transition between Virtual
Trust Levels (VTLs) in MSHV_VTL when the kernel acts as a paravisor.
Signed-off-by: Roman Kisel <[email protected]>
Reviewed-by: Roman Kisel <[email protected]>
Signed-off-by: Naman Jain <[email protected]>
---
arch/arm64/hyperv/Makefile | 1 +
arch/arm64/hyperv/hv_vtl.c | 158 ++++++++++++++++++++++++++++++
arch/arm64/include/asm/mshyperv.h | 13 +++
arch/x86/include/asm/mshyperv.h | 2 -
drivers/hv/mshv_vtl.h | 3 +
include/asm-generic/mshyperv.h | 2 +
6 files changed, 177 insertions(+), 2 deletions(-)
create mode 100644 arch/arm64/hyperv/hv_vtl.c
[snip]
diff --git a/arch/arm64/include/asm/mshyperv.h
b/arch/arm64/include/asm/mshyperv.h
index 585b23a26f1b..9eb0e5999f29 100644
--- a/arch/arm64/include/asm/mshyperv.h
+++ b/arch/arm64/include/asm/mshyperv.h
@@ -60,6 +60,18 @@ static inline u64 hv_get_non_nested_msr(unsigned int reg)
ARM_SMCCC_SMC_64, \
ARM_SMCCC_OWNER_VENDOR_HYP, \
HV_SMCCC_FUNC_NUMBER)
+
+struct mshv_vtl_cpu_context {
+/*
+ * x18 is managed by the hypervisor. It won't be reloaded from this array.
+ * It is included here for convenience in array indexing.
+ * 'rsvd' field serves as alignment padding so q[] starts at offset 32*8=256.
+ */
+ __u64 x[31];
+ __u64 rsvd;
+ __uint128_t q[32];
+};
+
#ifdef CONFIG_HYPERV_VTL_MODE
/*
* Get/Set the register. If the function returns `1`, that must be done via
@@ -69,6 +81,7 @@ static inline int hv_vtl_get_set_reg(struct hv_register_assoc
*regs,
bool set, b
{
return 1;
}
+
This appears to be a spurious blank line being added since there
are no other changes in the vicinity.
Acked.
#endif
#include <asm-generic/mshyperv.h>
diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index 08278547b84c..b4d80c9a673a 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -286,7 +286,6 @@ struct mshv_vtl_cpu_context {
#ifdef CONFIG_HYPERV_VTL_MODE
void __init hv_vtl_init_platform(void);
int __init hv_vtl_early_init(void);
-void mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0);
void mshv_vtl_return_call_init(u64 vtl_return_offset);
void mshv_vtl_return_hypercall(void);
void __mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0);
@@ -294,7 +293,6 @@ int hv_vtl_get_set_reg(struct hv_register_assoc *regs, bool
set,
bool shared);
#else
static inline void __init hv_vtl_init_platform(void) {}
static inline int __init hv_vtl_early_init(void) { return 0; }
-static inline void mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0) {}
static inline void mshv_vtl_return_call_init(u64 vtl_return_offset) {}
static inline void mshv_vtl_return_hypercall(void) {}
static inline void __mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0)
{}
diff --git a/drivers/hv/mshv_vtl.h b/drivers/hv/mshv_vtl.h
index a6eea52f7aa2..103f07371f3f 100644
--- a/drivers/hv/mshv_vtl.h
+++ b/drivers/hv/mshv_vtl.h
@@ -22,4 +22,7 @@ struct mshv_vtl_run {
char vtl_ret_actions[MSHV_MAX_RUN_MSG_SIZE];
};
+static_assert(sizeof(struct mshv_vtl_cpu_context) <= 1024,
+ "struct mshv_vtl_cpu_context exceeds reserved space in struct
mshv_vtl_run");
+
#endif /* _MSHV_VTL_H */
diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
index db183c8cfb95..8cdf2a9fbdfb 100644
--- a/include/asm-generic/mshyperv.h
+++ b/include/asm-generic/mshyperv.h
@@ -396,8 +396,10 @@ static inline int hv_deposit_memory(u64 partition_id, u64
status)
#if IS_ENABLED(CONFIG_HYPERV_VTL_MODE)
u8 __init get_vtl(void);
+void mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0);
#else
static inline u8 get_vtl(void) { return 0; }
+static inline void mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0) {}
Is this stub needed? Maybe I missed something, but it looks to me like none
of the code that calls this gets built unless CONFIG_HYPERV_VTL_MODE is set.
See further comments about stubs in Patch 8 of this series.
Config dependencies would handle such cases, and this is not required. I
saw similar stubs added in the code, so I thought this is a norm that
should be followed, and not rely on config dependencies.
I can remove it.
Regards,
Naman
