RE: [PATCH v2 07/15] arm64: hyperv: Add support for mshv_vtl_return_call

Michael Kelley
2026-04-27T05:39:04Z

From: Naman Jain <namjain@linux.microsoft.com> 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 <romank@linux.microsoft.com>
> Reviewed-by: Roman Kisel <vdso@mailbox.org>
> Signed-off-by: Naman Jain <namjain@linux.microsoft.com>
> ---
> 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.

> #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.

> #endif
>
> #endif
> --
> 2.43.0
>