[PATCH 08/11] Drivers: hv: mshv_vtl: Move register page config to arch-specific files
Naman Jain
namjain at linux.microsoft.com
Mon Apr 20 08:23:44 PDT 2026
On 4/1/2026 10:28 PM, Michael Kelley wrote:
> From: Naman Jain <namjain at linux.microsoft.com> Sent: Monday, March 16, 2026 5:13 AM
>>
>> Move mshv_vtl_configure_reg_page() implementation from
>> drivers/hv/mshv_vtl_main.c to arch-specific files:
>> - arch/x86/hyperv/hv_vtl.c: full implementation with register page setup
>> - arch/arm64/hyperv/hv_vtl.c: stub implementation (unsupported)
>>
>> Move common type definitions to include/asm-generic/mshyperv.h:
>> - struct mshv_vtl_per_cpu
>> - union hv_synic_overlay_page_msr
>>
>> Move hv_call_get_vp_registers() and hv_call_set_vp_registers()
>> declarations to include/asm-generic/mshyperv.h since these functions
>> are used by multiple modules.
>>
>> While at it, remove the unnecessary stub implementations in #else
>> case for mshv_vtl_return* functions in arch/x86/include/asm/mshyperv.h.
>
> Seems like this patch is doing multiple things. The reg page configuration
> changes are more substantial and should probably be in a patch by
> themselves. The other changes are more trivial and maybe are OK
> grouped into a single patch, but you could also consider breaking them
> out.
I will split this patch into 3 patches.
>
>>
>> This is essential for adding support for ARM64 in MSHV_VTL.
>>
>> Signed-off-by: Naman Jain <namjain at linux.microsoft.com>
>> ---
>> arch/arm64/hyperv/hv_vtl.c | 8 +++++
>> arch/arm64/include/asm/mshyperv.h | 3 ++
>> arch/x86/hyperv/hv_vtl.c | 32 ++++++++++++++++++++
>> arch/x86/include/asm/mshyperv.h | 7 ++---
>> drivers/hv/mshv.h | 8 -----
>> drivers/hv/mshv_vtl_main.c | 49 +++----------------------------
>> include/asm-generic/mshyperv.h | 42 ++++++++++++++++++++++++++
>> 7 files changed, 92 insertions(+), 57 deletions(-)
>>
>> diff --git a/arch/arm64/hyperv/hv_vtl.c b/arch/arm64/hyperv/hv_vtl.c
>> index 66318672c242..d699138427c1 100644
>> --- a/arch/arm64/hyperv/hv_vtl.c
>> +++ b/arch/arm64/hyperv/hv_vtl.c
>> @@ -10,6 +10,7 @@
>> #include <asm/boot.h>
>> #include <asm/mshyperv.h>
>> #include <asm/cpu_ops.h>
>> +#include <linux/export.h>
>>
>> void mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0)
>> {
>> @@ -142,3 +143,10 @@ void mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0)
>> "v24", "v25", "v26", "v27", "v28", "v29", "v30", "v31");
>> }
>> EXPORT_SYMBOL(mshv_vtl_return_call);
>> +
>> +bool hv_vtl_configure_reg_page(struct mshv_vtl_per_cpu *per_cpu)
>> +{
>> + pr_debug("Register page not supported on ARM64\n");
>> + return false;
>> +}
>> +EXPORT_SYMBOL_GPL(hv_vtl_configure_reg_page);
>> diff --git a/arch/arm64/include/asm/mshyperv.h
>> b/arch/arm64/include/asm/mshyperv.h
>> index de7f3a41a8ea..36803f0386cc 100644
>> --- a/arch/arm64/include/asm/mshyperv.h
>> +++ b/arch/arm64/include/asm/mshyperv.h
>> @@ -61,6 +61,8 @@ static inline u64 hv_get_non_nested_msr(unsigned int reg)
>> ARM_SMCCC_OWNER_VENDOR_HYP, \
>> HV_SMCCC_FUNC_NUMBER)
>>
>> +struct mshv_vtl_per_cpu;
>> +
>> struct mshv_vtl_cpu_context {
>> /*
>> * NOTE: x18 is managed by the hypervisor. It won't be reloaded from this array.
>> @@ -82,6 +84,7 @@ static inline int hv_vtl_get_set_reg(struct hv_register_assoc *regs,
>> bool set, u
>> }
>>
>> void mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0);
>> +bool hv_vtl_configure_reg_page(struct mshv_vtl_per_cpu *per_cpu);
>
> I think this declaration could be added in asm-generic/mshyperv.h so that it
> is shared by x86 and arm64. That also obviates the need for the forward
> ref to struct mshv_vtl_per_cpu that you've added here.
Acked.
>
>> #endif
>>
>> #include <asm-generic/mshyperv.h>
>> diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
>> index 72a0bb4ae0c7..ede290985d41 100644
>> --- a/arch/x86/hyperv/hv_vtl.c
>> +++ b/arch/x86/hyperv/hv_vtl.c
>> @@ -20,6 +20,7 @@
>> #include <uapi/asm/mtrr.h>
>> #include <asm/debugreg.h>
>> #include <linux/export.h>
>> +#include <linux/hyperv.h>
>> #include <../kernel/smpboot.h>
>> #include "../../kernel/fpu/legacy.h"
>>
>> @@ -259,6 +260,37 @@ int __init hv_vtl_early_init(void)
>> return 0;
>> }
>>
>> +static const union hv_input_vtl input_vtl_zero;
>> +
>> +bool hv_vtl_configure_reg_page(struct mshv_vtl_per_cpu *per_cpu)
>> +{
>> + struct hv_register_assoc reg_assoc = {};
>> + union hv_synic_overlay_page_msr overlay = {};
>> + struct page *reg_page;
>> +
>> + reg_page = alloc_page(GFP_KERNEL | __GFP_ZERO | __GFP_RETRY_MAYFAIL);
>> + if (!reg_page) {
>> + WARN(1, "failed to allocate register page\n");
>> + return false;
>> + }
>> +
>> + overlay.enabled = 1;
>> + overlay.pfn = page_to_hvpfn(reg_page);
>> + reg_assoc.name = HV_X64_REGISTER_REG_PAGE;
>> + reg_assoc.value.reg64 = overlay.as_uint64;
>> +
>> + if (hv_call_set_vp_registers(HV_VP_INDEX_SELF, HV_PARTITION_ID_SELF,
>> + 1, input_vtl_zero, ®_assoc)) {
>> + WARN(1, "failed to setup register page\n");
>> + __free_page(reg_page);
>> + return false;
>> + }
>> +
>> + per_cpu->reg_page = reg_page;
>> + return true;
>
> As Sashiko AI noted, the memory allocated for the reg_page never gets freed.
These are present in existing code, I'll address them in a separate series.
>
>> +}
>> +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)
>> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
>> index d5355a5b7517..d592fea49cdb 100644
>> --- a/arch/x86/include/asm/mshyperv.h
>> +++ b/arch/x86/include/asm/mshyperv.h
>> @@ -271,6 +271,8 @@ static inline u64 hv_get_non_nested_msr(unsigned int reg) {
>> return 0; }
>> static inline int hv_apicid_to_vp_index(u32 apic_id) { return -EINVAL; }
>> #endif /* CONFIG_HYPERV */
>>
>> +struct mshv_vtl_per_cpu;
>> +
>> struct mshv_vtl_cpu_context {
>> union {
>> struct {
>> @@ -305,13 +307,10 @@ 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);
>> int hv_vtl_get_set_reg(struct hv_register_assoc *regs, bool set, u64 shared);
>> +bool hv_vtl_configure_reg_page(struct mshv_vtl_per_cpu *per_cpu);
>
> Same as for arm64. Add a shared declaration in asm-generic/mshyperv.h.
Ditto.
>
>> #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) {}
>> #endif
>>
>> #include <asm-generic/mshyperv.h>
>> diff --git a/drivers/hv/mshv.h b/drivers/hv/mshv.h
>> index d4813df92b9c..0fcb7f9ba6a9 100644
>> --- a/drivers/hv/mshv.h
>> +++ b/drivers/hv/mshv.h
>> @@ -14,14 +14,6 @@
>> memchr_inv(&((STRUCT).MEMBER), \
>> 0, sizeof_field(typeof(STRUCT), MEMBER))
>>
>> -int hv_call_get_vp_registers(u32 vp_index, u64 partition_id, u16 count,
>> - union hv_input_vtl input_vtl,
>> - struct hv_register_assoc *registers);
>> -
>> -int hv_call_set_vp_registers(u32 vp_index, u64 partition_id, u16 count,
>> - union hv_input_vtl input_vtl,
>> - struct hv_register_assoc *registers);
>> -
>> int hv_call_get_partition_property(u64 partition_id, u64 property_code,
>> u64 *property_value);
>>
>> diff --git a/drivers/hv/mshv_vtl_main.c b/drivers/hv/mshv_vtl_main.c
>> index 91517b45d526..c79d24317b8e 100644
>> --- a/drivers/hv/mshv_vtl_main.c
>> +++ b/drivers/hv/mshv_vtl_main.c
>> @@ -78,21 +78,6 @@ struct mshv_vtl {
>> u64 id;
>> };
>>
>> -struct mshv_vtl_per_cpu {
>> - struct mshv_vtl_run *run;
>> - struct page *reg_page;
>> -};
>> -
>> -/* SYNIC_OVERLAY_PAGE_MSR - internal, identical to hv_synic_simp */
>> -union hv_synic_overlay_page_msr {
>> - u64 as_uint64;
>> - struct {
>> - u64 enabled: 1;
>> - u64 reserved: 11;
>> - u64 pfn: 52;
>> - } __packed;
>> -};
>> -
>> 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;
>> @@ -201,34 +186,6 @@ static struct page *mshv_vtl_cpu_reg_page(int cpu)
>> return *per_cpu_ptr(&mshv_vtl_per_cpu.reg_page, cpu);
>> }
>>
>> -static void mshv_vtl_configure_reg_page(struct mshv_vtl_per_cpu *per_cpu)
>> -{
>> - struct hv_register_assoc reg_assoc = {};
>> - union hv_synic_overlay_page_msr overlay = {};
>> - struct page *reg_page;
>> -
>> - reg_page = alloc_page(GFP_KERNEL | __GFP_ZERO | __GFP_RETRY_MAYFAIL);
>> - if (!reg_page) {
>> - WARN(1, "failed to allocate register page\n");
>> - return;
>> - }
>> -
>> - overlay.enabled = 1;
>> - overlay.pfn = page_to_hvpfn(reg_page);
>> - reg_assoc.name = HV_X64_REGISTER_REG_PAGE;
>> - reg_assoc.value.reg64 = overlay.as_uint64;
>> -
>> - if (hv_call_set_vp_registers(HV_VP_INDEX_SELF, HV_PARTITION_ID_SELF,
>> - 1, input_vtl_zero, ®_assoc)) {
>> - WARN(1, "failed to setup register page\n");
>> - __free_page(reg_page);
>> - return;
>> - }
>> -
>> - per_cpu->reg_page = reg_page;
>> - mshv_has_reg_page = true;
>> -}
>> -
>> static void mshv_vtl_synic_enable_regs(unsigned int cpu)
>> {
>> union hv_synic_sint sint;
>> @@ -329,8 +286,10 @@ static int mshv_vtl_alloc_context(unsigned int cpu)
>> if (!per_cpu->run)
>> return -ENOMEM;
>>
>> - if (mshv_vsm_capabilities.intercept_page_available)
>> - mshv_vtl_configure_reg_page(per_cpu);
>> + if (mshv_vsm_capabilities.intercept_page_available) {
>> + if (hv_vtl_configure_reg_page(per_cpu))
>> + mshv_has_reg_page = true;
>
> As Sashiko AI noted, it doesn't work to use the global mshv_has_reg_page
> to indicate the success of configuring the reg page, which is a per-cpu
> operation. But this bug existed before this patch set, so maybe it should
> be fixed as a preliminary patch.
Acked. Will address them in a separate series.
>
>> + }
>>
>> mshv_vtl_synic_enable_regs(cpu);
>>
>> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
>> index b147a12085e4..b53fcc071596 100644
>> --- a/include/asm-generic/mshyperv.h
>> +++ b/include/asm-generic/mshyperv.h
>> @@ -383,8 +383,50 @@ static inline int hv_deposit_memory(u64 partition_id, u64 status)
>> return hv_deposit_memory_node(NUMA_NO_NODE, partition_id, status);
>> }
>>
>> +#if IS_ENABLED(CONFIG_MSHV_ROOT) || IS_ENABLED(CONFIG_MSHV_VTL)
>> +int hv_call_get_vp_registers(u32 vp_index, u64 partition_id, u16 count,
>> + union hv_input_vtl input_vtl,
>> + struct hv_register_assoc *registers);
>> +
>> +int hv_call_set_vp_registers(u32 vp_index, u64 partition_id, u16 count,
>> + union hv_input_vtl input_vtl,
>> + struct hv_register_assoc *registers);
>> +#else
>> +static inline int hv_call_get_vp_registers(u32 vp_index, u64 partition_id,
>> + u16 count,
>> + union hv_input_vtl input_vtl,
>> + struct hv_register_assoc *registers)
>> +{
>> + return -EOPNOTSUPP;
>> +}
>> +
>> +static inline int hv_call_set_vp_registers(u32 vp_index, u64 partition_id,
>> + u16 count,
>> + union hv_input_vtl input_vtl,
>> + struct hv_register_assoc *registers)
>> +{
>> + return -EOPNOTSUPP;
>> +}
>> +#endif /* CONFIG_MSHV_ROOT || CONFIG_MSHV_VTL */
>> +
>> #define HV_VP_ASSIST_PAGE_ADDRESS_SHIFT 12
>> +
>> #if IS_ENABLED(CONFIG_HYPERV_VTL_MODE)
>> +struct mshv_vtl_per_cpu {
>> + struct mshv_vtl_run *run;
>> + struct page *reg_page;
>> +};
>> +
>> +/* SYNIC_OVERLAY_PAGE_MSR - internal, identical to hv_synic_simp */
>> +union hv_synic_overlay_page_msr {
>> + u64 as_uint64;
>> + struct {
>> + u64 enabled: 1;
>> + u64 reserved: 11;
>> + u64 pfn: 52;
>> + } __packed;
>> +};
>> +
>> u8 __init get_vtl(void);
>> #else
>> static inline u8 get_vtl(void) { return 0; }
>> --
>> 2.43.0
>>
>
> Sashiko AI noted another existing bug in mshv_vtl_init(), which is that
> the error path does kfree(mem_dev) when it should do
> put_device(mem_dev). See the comment in the header of
> device_initialize().
To avoid this series bloating up, I am thinking of taking up these fixes
in a separate series.
Regards,
Naman
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