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 10:18 AM, Saurabh Singh Sengar wrote:
>   
>> 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.
>>
> 
> 
> hyperv-fixes is broken too, here's the log for your ref:
> 
> https://dashboard.kernelci.org/log-viewer?itemId=microsoft%3A20250425085833916790&o=microsoft&type=build&url=https%3A%2F%2Flisalogsb15850d3.blob.core.windows.net%2Flisa-logs%2Fdefault_default%2F20250425%2F20250425-085110-393%2Fkernel_installer%2Fbuild.log%3Fst%3D2025-04-25T09%253A09%253A35Z%26se%3D2025-05-02T09%253A09%253A35Z%26sp%3Dr%26sv%3D2024-11-04%26sr%3Db%26skoid%3D14b53b1d-f4fc-442e-a437-4989376b1754%26sktid%3D72f988bf-86f1-41af-91ab-2d7cd011db47%26skt%3D2025-04-25T09%253A09%253A35Z%26ske%3D2025-05-02T09%253A09%253A35Z%26sks%3Db%26skv%3D2024-11-04%26sig%3DZHfA7%2FC174KR6HT8zhchCb47NE1aceqw8h0APzKxsII%253D
> 
> The hv_snp_boot_ap() function in arch/x86/hyperv/ivm.c currently fails to compile.
> It looks like the function's argument was changed from 'cpu' to 'apic_id', but internal
> references to cpu were not updated accordingly.
> 
> This might have gone unnoticed during your testing if CONFIG_AMD_MEM_ENCRYPT
> was disabled, in which case this function wouldn't have been compiled.

Must be the case! I did run the command to merge the CVM specific config
options but I didn't check the result.

Yep, I see the issue. Will resend the patch.

> 
> Regards,
> Saurabh

-- 
Thank you,
Roman