RE: [PATCH 10/11] Drivers: hv: Add support for arm64 in MSHV_VTL

Michael Kelley
2026-04-01T16:58:57Z

From: Naman Jain <namjain@linux.microsoft.com> Sent: Monday, March 16, 2026 5:13 AM
>
> Add necessary support to make MSHV_VTL work for arm64 architecture.
> * Add stub implementation for mshv_vtl_return_call_init(): not required
> for arm64
> * Remove fpu/legacy.h header inclusion, as this is not required
> * handle HV_REGISTER_VSM_CODE_PAGE_OFFSETS register: not supported
> in arm64
> * Configure custom percpu_vmbus_handler by using
> hv_setup_percpu_vmbus_handler()
> * Handle hugepage functions by config checks
>
> Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
> Signed-off-by: Naman Jain <namjain@linux.microsoft.com>
> ---
> arch/arm64/include/asm/mshyperv.h | 2 ++
> drivers/hv/mshv_vtl_main.c | 21 ++++++++++++++-------
> 2 files changed, 16 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm64/include/asm/mshyperv.h
> b/arch/arm64/include/asm/mshyperv.h
> index 36803f0386cc..027a7f062d70 100644
> --- a/arch/arm64/include/asm/mshyperv.h
> +++ b/arch/arm64/include/asm/mshyperv.h
> @@ -83,6 +83,8 @@ static inline int hv_vtl_get_set_reg(struct hv_register_assoc *regs, bool set, u
> return 1;
> }
>
> +static inline void mshv_vtl_return_call_init(u64 vtl_return_offset) {}
> +
> void mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0);
> bool hv_vtl_configure_reg_page(struct mshv_vtl_per_cpu *per_cpu);
> #endif
> diff --git a/drivers/hv/mshv_vtl_main.c b/drivers/hv/mshv_vtl_main.c
> index 4c9ae65ad3e8..5702fe258500 100644
> --- a/drivers/hv/mshv_vtl_main.c
> +++ b/drivers/hv/mshv_vtl_main.c
> @@ -23,8 +23,6 @@
> #include <trace/events/ipi.h>
> #include <uapi/linux/mshv.h>
> #include <hyperv/hvhdk.h>
> -
> -#include "../../kernel/fpu/legacy.h"

Was there a particular code change that made this unnecessary? Or was it
unnecessary from the start of this source code file? Just curious ....

> #include "mshv.h"
> #include "mshv_vtl.h"
> #include "hyperv_vmbus.h"
> @@ -206,18 +204,21 @@ static void mshv_vtl_synic_enable_regs(unsigned int cpu)
> static int mshv_vtl_get_vsm_regs(void)
> {
> struct hv_register_assoc registers[2];
> - int ret, count = 2;
> + int ret, count = 0;
>
> - registers[0].name = HV_REGISTER_VSM_CODE_PAGE_OFFSETS;
> - registers[1].name = HV_REGISTER_VSM_CAPABILITIES;
> + registers[count++].name = HV_REGISTER_VSM_CAPABILITIES;
> + /* Code page offset register is not supported on ARM */
> + if (IS_ENABLED(CONFIG_X86_64))
> + registers[count++].name = HV_REGISTER_VSM_CODE_PAGE_OFFSETS;
>
> ret = hv_call_get_vp_registers(HV_VP_INDEX_SELF, HV_PARTITION_ID_SELF,
> count, input_vtl_zero, registers);
> 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 = registers[0].value.reg64;
> + if (IS_ENABLED(CONFIG_X86_64))
> + mshv_vsm_page_offsets.as_uint64 = registers[1].value.reg64;
>
> return ret;
> }

This function has gotten somewhat messy to handle the x86 and arm64
differences. Let me suggest a different approach. Have this function only
get the VSM capabilities register, as that is generic across x86 and
arm64. Then, update x86 mshv_vtl_return_call_init() to get the
PAGE_OFFSETS register and then immediately use the value to update
the static call. The global variable mshv_vms_page_offsets is no longer
necessary.

My suggestion might be little more code because hv_call_get_vp_registers()
is invoked in two different places. But it cleanly separates the two use
cases, and keeps the x86 hackery under arch/x86.

> @@ -280,10 +281,13 @@ static int hv_vtl_setup_synic(void)
>
> /* Use our isr to first filter out packets destined for userspace */
> hv_setup_vmbus_handler(mshv_vtl_vmbus_isr);
> + /* hv_setup_vmbus_handler() is stubbed for ARM64, add per-cpu VMBus handlers instead */
> + hv_setup_percpu_vmbus_handler(mshv_vtl_vmbus_isr);
>
> ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "hyperv/vtl:online",
> mshv_vtl_alloc_context, NULL);
> if (ret < 0) {
> + hv_setup_percpu_vmbus_handler(vmbus_isr);
> hv_setup_vmbus_handler(vmbus_isr);
> return ret;
> }
> @@ -296,6 +300,7 @@ static int hv_vtl_setup_synic(void)
> static void hv_vtl_remove_synic(void)
> {
> cpuhp_remove_state(mshv_vtl_cpuhp_online);
> + hv_setup_percpu_vmbus_handler(vmbus_isr);
> hv_setup_vmbus_handler(vmbus_isr);
> }
>
> @@ -1080,10 +1085,12 @@ static vm_fault_t mshv_vtl_low_huge_fault(struct vm_fault *vmf, unsigned int ord
> ret = vmf_insert_pfn_pmd(vmf, pfn, vmf->flags & FAULT_FLAG_WRITE);
> return ret;
>
> +#if defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
> case PUD_ORDER:
> if (can_fault(vmf, PUD_SIZE, &pfn))
> ret = vmf_insert_pfn_pud(vmf, pfn, vmf->flags & FAULT_FLAG_WRITE);
> return ret;
> +#endif
>
> default:
> return VM_FAULT_SIGBUS;
> --
> 2.43.0