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

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Message-ID: <dee3a22e-935c-4500-b9d1-b43109f4897a@linux.microsoft.com>
Date: Fri, 5 Sep 2025 11:49:18 -0700
From: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
To: Praveen K Paladugu <praveenkpaladugu@...il.com>,
 linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: 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 9/5/2025 8:43 AM, Praveen K Paladugu wrote:
> 
> 
> On 8/28/2025 7:43 PM, Nuno Das Neves 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
> nit: s/xx/Some hypervisor APIs are gated by feature bits exposed in
> "vmm capabilities" partition property./g

Thanks, I'll update it for v2

Nuno

>> 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>
>> ---
>>   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;
> 
> Reviewed-by: Praveen K Paladugu <prapal@...ux.microsoft.com>