Re: [EXTERNAL] Re: [PATCH hyperv-next] x86/hyperv: Fix APIC ID and VP ID confusion in hv_snp_boot_ap()

[Roman Kisel <romank@linux.microsoft.com>]

On 4/25/2025 2:14 AM, Saurabh Singh Sengar wrote:
>>
>> On Thu, Apr 24, 2025 at 02:57:46PM -0700, Roman Kisel wrote:
>>> To start an application processor in SNP-isolated guest, a hypercall
>>> is used that takes a virtual processor index. The hv_snp_boot_ap()
>>> function uses that START_VP hypercall but passes as VP ID to it what
>>> it receives as a wakeup_secondary_cpu_64 callback: the APIC ID.
>>>
>>> As those two aren't generally interchangeable, that may lead to hung
>>> APs if VP IDs and APIC IDs don't match, e.g. APIC IDs might be sparse
>>> whereas VP IDs never are.
>>>
>>> Update the parameter names to avoid confusion as to what the parameter
>>> is. Use the APIC ID to VP ID conversion to provide correct input to
>>> the hypercall.
>>>
>>> Cc: stable@vger.kernel.org
>>> Fixes: 44676bb9d566 ("x86/hyperv: Add smp support for SEV-SNP guest")
>>> Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
>>
>> Applied to hyperv-fixes.
> 
> This patch will break the builds.
> 
> Roman,
> Have you tested this patch on the latest linux-next ?

Thanks for your help! Only on hyperv-next, looking how to repro and fix
on linux-next. The kernel robot was happy, or I am missing some context
about how the robot works...

What was your kernel configuration, or just anything that enables
Hyper-V?

I thought the the linux-next tree would be a subset of hyper-next
so should work, realizing that have to check, likely there might be
changes from other trees.

> 
> Regards,
> Saurabh
> 

-- 
Thank you,
Roman