From: Jinank Jain <jinankjain@xxxxxxxxxxxxxxxxxxx> Sent: Wednesday, November 2, 2022 9:36 AM
>
The email subject prefix for a patch like this is usually "x86/hyperv"
Check the commit log for arch/x86/kernel/cpu/mshyperv.c, and you'll see
what is usually done. It's best to maintain consistency.
Same comment applies to other patches in this series: Check the
commit log for the relevant files and pick the prefix that fits best.
> 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 +++++++
> 3 files changed, 12 insertions(+)
>
> 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..29388567eafd 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -190,6 +190,8 @@ static inline void hv_ghcb_terminate(unsigned int set, unsigned int reason) {}
>
> extern bool hv_isolation_type_snp(void);
>
> +extern bool hv_nested;
> +
> static inline bool hv_is_synic_reg(unsigned int reg)
> {
> if ((reg >= HV_REGISTER_SCONTROL) &&
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index 831613959a92..2555535f5237 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;
This reference to hv_nested will cause problems similar to what happens
with hv_root_partition. See the comments in hv_common.c about how
hv_root_partition is handled. I think you'll need to do the same thing
with hv_nested.
> + pr_info("Hyper-V: Linux running on a nested hypervisor\n");
A nit: Let's drop the word "Linux" from the above message so it is
consistent with the previous message about "running as root partition".
> + }
> +
> /*
> * Extract host information.
> */
> --
> 2.25.1
