On Thu, Nov 03, 2022 at 01:04:03PM +0000, Jinank Jain wrote:
> When Linux runs as a root partition for Microsoft Hypervisor. It is
> possible to detect if it is running as nested hypervisor using
> hints exposed by mshv. While at it expose a new variable called
> hv_nested which can be used later for making decisions specific to
> nested use case.
>
> Signed-off-by: Jinank Jain <jinankjain@xxxxxxxxxxxxxxxxxxx>
> ---
> arch/x86/include/asm/hyperv-tlfs.h | 3 +++
> arch/x86/include/asm/mshyperv.h | 2 ++
> arch/x86/kernel/cpu/mshyperv.c | 7 +++++++
> drivers/hv/hv_common.c | 7 +++++--
> 4 files changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
> index 3089ec352743..d9a611565859 100644
> --- a/arch/x86/include/asm/hyperv-tlfs.h
> +++ b/arch/x86/include/asm/hyperv-tlfs.h
> @@ -114,6 +114,9 @@
> /* Recommend using the newer ExProcessorMasks interface */
> #define HV_X64_EX_PROCESSOR_MASKS_RECOMMENDED BIT(11)
>
> +/* Indicates that the hypervisor is nested within a Hyper-V partition. */
> +#define HV_X64_HYPERV_NESTED BIT(12)
> +
> /* Recommend using enlightened VMCS */
> #define HV_X64_ENLIGHTENED_VMCS_RECOMMENDED BIT(14)
>
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index 61f0c206bff0..3c39923e5969 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -26,6 +26,8 @@ void hyperv_vector_handler(struct pt_regs *regs);
> #if IS_ENABLED(CONFIG_HYPERV)
> extern int hyperv_init_cpuhp;
>
> +extern bool hv_nested;
> +
> extern void *hv_hypercall_pg;
>
> extern u64 hv_current_partition_id;
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index 831613959a92..9a4204139490 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -37,6 +37,8 @@
>
> /* Is Linux running as the root partition? */
> bool hv_root_partition;
> +/* Is Linux running on nested Microsoft Hypervisor */
> +bool hv_nested;
> struct ms_hyperv_info ms_hyperv;
>
> #if IS_ENABLED(CONFIG_HYPERV)
> @@ -301,6 +303,11 @@ static void __init ms_hyperv_init_platform(void)
> pr_info("Hyper-V: running as root partition\n");
> }
>
> + if (ms_hyperv.hints & HV_X64_HYPERV_NESTED) {
> + hv_nested = true;
> + pr_info("Hyper-V: running on a nested hypervisor\n");
> + }
> +
> /*
> * Extract host information.
> */
> diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
> index ae68298c0dca..dcb336ce374f 100644
> --- a/drivers/hv/hv_common.c
> +++ b/drivers/hv/hv_common.c
> @@ -25,8 +25,8 @@
> #include <asm/mshyperv.h>
>
> /*
> - * hv_root_partition and ms_hyperv are defined here with other Hyper-V
> - * specific globals so they are shared across all architectures and are
> + * hv_root_partition, ms_hyperv and hv_nested are defined here with other
> + * Hyper-V specific globals so they are shared across all architectures and are
> * built only when CONFIG_HYPERV is defined. But on x86,
> * ms_hyperv_init_platform() is built even when CONFIG_HYPERV is not
> * defined, and it uses these two variables. So mark them as __weak
> @@ -36,6 +36,9 @@
> bool __weak hv_root_partition;
> EXPORT_SYMBOL_GPL(hv_root_partition);
>
> +bool __weak hv_nested;
> +EXPORT_SYMBOL_GPL(hv_nested);
> +
> struct ms_hyperv_info __weak ms_hyperv;
> EXPORT_SYMBOL_GPL(ms_hyperv);
>
> --
> 2.25.1
Reviewed-by: <anrayabh@xxxxxxxxxxxxxxxxxxx>
