linux-kernel - Re: [PATCH 4/6] mshv: Get the vmm capabilities offered by the hypervisor

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Message-ID: <CAMvTesD0hOxh5NpqqELkWeKmwfZ0dSdiYSvXKFg4K50e0KtkOg@mail.gmail.com>
Date: Sun, 7 Sep 2025 01:34:56 +0800
From: Tianyu Lan <ltykernel@...il.com>
To: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
Cc: linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org, 
	kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org, 
	mhklinux@...look.com, decui@...rosoft.com, paekkaladevi@...ux.microsoft.com
Subject: Re: [PATCH 4/6] mshv: Get the vmm capabilities offered by the hypervisor

On Fri, Aug 29, 2025 at 8:44 AM Nuno Das Neves
<nunodasneves@...ux.microsoft.com> wrote:
>
> From: Purna Pavan Chandra Aekkaladevi <paekkaladevi@...ux.microsoft.com>
>
> Some newer hypervisor APIs are gated by feature bits in the so-called
> "vmm capabilities" partition property. Store the capabilities on
> mshv_root module init, using HVCALL_GET_PARTITION_PROPERTY_EX.
>
> Signed-off-by: Purna Pavan Chandra Aekkaladevi <paekkaladevi@...ux.microsoft.com>
> Signed-off-by: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
> ---

Reviewed-by: Tianyu Lan <tiala@...rosoft.com>

>  drivers/hv/mshv_root.h      |  1 +
>  drivers/hv/mshv_root_main.c | 28 ++++++++++++++++++++++++++++
>  2 files changed, 29 insertions(+)
>
> diff --git a/drivers/hv/mshv_root.h b/drivers/hv/mshv_root.h
> index 4aeb03bea6b6..0cb1e2589fe1 100644
> --- a/drivers/hv/mshv_root.h
> +++ b/drivers/hv/mshv_root.h
> @@ -178,6 +178,7 @@ struct mshv_root {
>         struct hv_synic_pages __percpu *synic_pages;
>         spinlock_t pt_ht_lock;
>         DECLARE_HASHTABLE(pt_htable, MSHV_PARTITIONS_HASH_BITS);
> +       struct hv_partition_property_vmm_capabilities vmm_caps;
>  };
>
>  /*
> diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c
> index 56ababab57ce..29f61ecc9771 100644
> --- a/drivers/hv/mshv_root_main.c
> +++ b/drivers/hv/mshv_root_main.c
> @@ -2327,6 +2327,28 @@ static int __init mshv_root_partition_init(struct device *dev)
>         return err;
>  }
>
> +static int mshv_init_vmm_caps(struct device *dev)
> +{
> +       int ret;
> +
> +       memset(&mshv_root.vmm_caps, 0, sizeof(mshv_root.vmm_caps));
> +       ret = hv_call_get_partition_property_ex(HV_PARTITION_ID_SELF,
> +                                               HV_PARTITION_PROPERTY_VMM_CAPABILITIES,
> +                                               0, &mshv_root.vmm_caps,
> +                                               sizeof(mshv_root.vmm_caps));
> +
> +       /*
> +        * HV_PARTITION_PROPERTY_VMM_CAPABILITIES is not supported in
> +        * older hyperv. Ignore the -EIO error code.
> +        */
> +       if (ret && ret != -EIO)
> +               return ret;
> +
> +       dev_dbg(dev, "vmm_caps=0x%llx\n", mshv_root.vmm_caps.as_uint64[0]);
> +
> +       return 0;
> +}
> +
>  static int __init mshv_parent_partition_init(void)
>  {
>         int ret;
> @@ -2377,6 +2399,12 @@ static int __init mshv_parent_partition_init(void)
>         if (ret)
>                 goto remove_cpu_state;
>
> +       ret = mshv_init_vmm_caps(dev);
> +       if (ret) {
> +               dev_err(dev, "Failed to get VMM capabilities\n");
> +               goto exit_partition;
> +       }
> +
>         ret = mshv_irqfd_wq_init();
>         if (ret)
>                 goto exit_partition;
> --
> 2.34.1
>
>


-- 
Thanks
Tianyu Lan