From: Jinank Jain <jinankjain@xxxxxxxxxxxxxxxxxxx> Sent: Sunday, January 1, 2023 11:13 PM
>
> Detect if Linux is running as a nested hypervisor in the root
> partition for Microsoft Hypervisor, using flags provided by MSHV.
> Expose a new variable hv_nested that is used later for decisions
> specific to the nested use case.
>
> Signed-off-by: Jinank Jain <jinankjain@xxxxxxxxxxxxxxxxxxx>
> ---
> arch/x86/include/asm/hyperv-tlfs.h | 3 +++
> arch/x86/kernel/cpu/mshyperv.c | 7 +++++++
> drivers/hv/hv_common.c | 9 ++++++---
> include/asm-generic/mshyperv.h | 1 +
> 4 files changed, 17 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
> index 6d9368ea3701..58c03d18c235 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/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index 46668e255421..f9b78d4829e3 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..52a6f89ccdbd 100644
> --- a/drivers/hv/hv_common.c
> +++ b/drivers/hv/hv_common.c
> @@ -25,17 +25,20 @@
> #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
> + * defined, and it uses these three variables. So mark them as __weak
> * here, allowing for an overriding definition in the module containing
> * ms_hyperv_init_platform().
> */
> 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);
>
> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
> index bfb9eb9d7215..f131027830c3 100644
> --- a/include/asm-generic/mshyperv.h
> +++ b/include/asm-generic/mshyperv.h
> @@ -48,6 +48,7 @@ struct ms_hyperv_info {
> u64 shared_gpa_boundary;
> };
> extern struct ms_hyperv_info ms_hyperv;
> +extern bool hv_nested;
>
> extern void * __percpu *hyperv_pcpu_input_arg;
> extern void * __percpu *hyperv_pcpu_output_arg;
> --
> 2.25.1
Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
