linux-kernel - Re: [PATCH 1/4] PCI: hv: Do not do vmbus initialization on baremetal

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Message-ID: <38127f1a-3761-48c7-8e95-1f677d6bd7b3@linux.microsoft.com>
Date: Mon, 16 Jun 2025 13:06:20 -0700
From: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
To: Michael Kelley <mhklinux@...look.com>,
 "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
 "linux-arm-kernel@...ts.infradead.org"
 <linux-arm-kernel@...ts.infradead.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Cc: "kys@...rosoft.com" <kys@...rosoft.com>,
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Subject: Re: [PATCH 1/4] PCI: hv: Do not do vmbus initialization on baremetal

On 6/11/2025 4:06 PM, Michael Kelley wrote:
> From: Nuno Das Neves <nunodasneves@...ux.microsoft.com> Sent: Tuesday, June 10, 2025 4:52 PM
>>
>> From: Mukesh Rathor <mrathor@...ux.microsoft.com>
> 
> The patch Subject line is confusing to me. Perhaps this better captures
> the intent:
> 
>  "PCI: hv: Don't load the driver for the root partition on a bare-metal hypervisor"
> 

Thanks, that does make more sense.

>>
>> init_hv_pci_drv() is not relevant for root partition on baremetal as there
>> is no vmbus. On nested (with a Windows L1 root), vmbus is present.
> 
> This needs more precision. init_hv_pci_drv() isn't what is
> "not relevant". It's the entire driver that doesn't need to be loaded
> because the root partition on a bare-metal hypervisor doesn't use
> VMBus. It's only when the root partition is running on a nested
> hypervisor that it uses VMBus, and hence may need the Hyper-V
> PCI driver to be loaded.
> 

I'll update it so it is clearer, thanks.

>>
>> Signed-off-by: Mukesh Rathor <mrathor@...ux.microsoft.com>
>> Signed-off-by: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
>> ---
>>  drivers/pci/controller/pci-hyperv.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
>> index b4f29ee75848..4d25754dfe2f 100644
>> --- a/drivers/pci/controller/pci-hyperv.c
>> +++ b/drivers/pci/controller/pci-hyperv.c
>> @@ -4150,6 +4150,9 @@ static int __init init_hv_pci_drv(void)
>>  	if (!hv_is_hyperv_initialized())
>>  		return -ENODEV;
>>
>> +	if (hv_root_partition() && !hv_nested)
>> +		return -ENODEV;
>> +
>>  	ret = hv_pci_irqchip_init();
>>  	if (ret)
>>  		return ret;
>> --
>> 2.34.1