RE: [PATCH v2 12/15] mshv_vtl: Move VSM code page offset logic to x86 files

Michael Kelley
2026-04-27T05:41:06Z

From: Naman Jain <namjain@linux.microsoft.com> Sent: Thursday, April 23, 2026 5:42 AM
>
> The VSM code page offset register (HV_REGISTER_VSM_CODE_PAGE_OFFSETS)
> is x86 specific, its value configures the static call used to return
> to VTL0 via the hypercall page. Move the register read from the common
> mshv_vtl_get_vsm_regs() into the x86 mshv_vtl_return_call_init(),
> which is the sole consumer of the offset.
>
> Change mshv_vtl_return_call_init() from taking a u64 parameter
> to taking no arguments, and rename mshv_vtl_get_vsm_regs() to
> mshv_vtl_get_vsm_cap_reg() since it now only fetches
> HV_REGISTER_VSM_CAPABILITIES.
>
> No functional change on x86. This prepares the common driver code for
> ARM64 where VSM code page offsets do not apply.
>
> Signed-off-by: Naman Jain <namjain@linux.microsoft.com>
> ---
> arch/x86/hyperv/hv_vtl.c | 19 +++++++++++++++++--
> arch/x86/include/asm/mshyperv.h | 4 ++--
> drivers/hv/mshv_vtl_main.c | 24 +++++++++++++-----------
> 3 files changed, 32 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
> index f3ffb6a7cb2d..7c10b34cf8a4 100644
> --- a/arch/x86/hyperv/hv_vtl.c
> +++ b/arch/x86/hyperv/hv_vtl.c
> @@ -293,10 +293,25 @@ EXPORT_SYMBOL_GPL(hv_vtl_configure_reg_page);
>
> DEFINE_STATIC_CALL_NULL(__mshv_vtl_return_hypercall, void (*)(void));
>
> -void mshv_vtl_return_call_init(u64 vtl_return_offset)
> +int mshv_vtl_return_call_init(void)
> {
> + struct hv_register_assoc vsm_pg_offset_reg;
> + union hv_register_vsm_page_offsets offsets;
> + int ret;
> +
> + vsm_pg_offset_reg.name = HV_REGISTER_VSM_CODE_PAGE_OFFSETS;
> +
> + ret = hv_call_get_vp_registers(HV_VP_INDEX_SELF, HV_PARTITION_ID_SELF,
> + 1, input_vtl_zero, &vsm_pg_offset_reg);
> + if (ret)
> + return ret;
> +
> + offsets.as_uint64 = vsm_pg_offset_reg.value.reg64;
> +
> static_call_update(__mshv_vtl_return_hypercall,
> - (void *)((u8 *)hv_hypercall_pg + vtl_return_offset));
> + (void *)((u8 *)hv_hypercall_pg + offsets.vtl_return_offset));
> +
> + return 0;
> }
> EXPORT_SYMBOL(mshv_vtl_return_call_init);
>
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index b4d80c9a673a..b48f115c1292 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -286,14 +286,14 @@ 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_init(u64 vtl_return_offset);
> +int mshv_vtl_return_call_init(void);
> void mshv_vtl_return_hypercall(void);
> void __mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0);
> 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_init(u64 vtl_return_offset) {}
> +static inline int mshv_vtl_return_call_init(void) { return 0; }
> static inline void mshv_vtl_return_hypercall(void) {}
> static inline void __mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0) {}
> #endif
> diff --git a/drivers/hv/mshv_vtl_main.c b/drivers/hv/mshv_vtl_main.c
> index 4c9ae65ad3e8..be498c9234fd 100644
> --- a/drivers/hv/mshv_vtl_main.c
> +++ b/drivers/hv/mshv_vtl_main.c
> @@ -79,7 +79,6 @@ struct mshv_vtl {
> };
>
> static struct mutex mshv_vtl_poll_file_lock;
> -static union hv_register_vsm_page_offsets mshv_vsm_page_offsets;
> static union hv_register_vsm_capabilities mshv_vsm_capabilities;
>
> static DEFINE_PER_CPU(struct mshv_vtl_poll_file, mshv_vtl_poll_file);
> @@ -203,21 +202,19 @@ static void mshv_vtl_synic_enable_regs(unsigned int cpu)
> /* VTL2 Host VSP SINT is (un)masked when the user mode requests that */
> }
>
> -static int mshv_vtl_get_vsm_regs(void)
> +static int mshv_vtl_get_vsm_cap_reg(void)
> {
> - struct hv_register_assoc registers[2];
> - int ret, count = 2;
> + struct hv_register_assoc vsm_capability_reg;
> + int ret;
>
> - registers[0].name = HV_REGISTER_VSM_CODE_PAGE_OFFSETS;
> - registers[1].name = HV_REGISTER_VSM_CAPABILITIES;
> + vsm_capability_reg.name = HV_REGISTER_VSM_CAPABILITIES;
>
> ret = hv_call_get_vp_registers(HV_VP_INDEX_SELF, HV_PARTITION_ID_SELF,
> - count, input_vtl_zero, registers);
> + 1, input_vtl_zero, &vsm_capability_reg);
> if (ret)
> return ret;
>
> - mshv_vsm_page_offsets.as_uint64 = registers[0].value.reg64;
> - mshv_vsm_capabilities.as_uint64 = registers[1].value.reg64;
> + mshv_vsm_capabilities.as_uint64 = vsm_capability_reg.value.reg64;
>
> return ret;

Nit: This could be just "return 0".

> }
> @@ -1139,13 +1136,18 @@ static int __init mshv_vtl_init(void)
> tasklet_init(&msg_dpc, mshv_vtl_sint_on_msg_dpc, 0);
> init_waitqueue_head(&fd_wait_queue);
>
> - if (mshv_vtl_get_vsm_regs()) {
> + if (mshv_vtl_get_vsm_cap_reg()) {
> dev_emerg(dev, "Unable to get VSM capabilities !!\n");

Why is this failure an emergency message, while the other failures
here in mshv_vtl_init() are just error messages? When there's lack
of consistency, I always wonder if there is a reason ..... :-)

> ret = -ENODEV;
> goto free_dev;
> }
>
> - mshv_vtl_return_call_init(mshv_vsm_page_offsets.vtl_return_offset);
> + ret = mshv_vtl_return_call_init();
> + if (ret) {
> + dev_err(dev, "mshv_vtl_return_call_init failed: %d\n", ret);
> + goto free_dev;
> + }
> +
> ret = hv_vtl_setup_synic();
> if (ret)
> goto free_dev;
> --
> 2.43.0
>