linux-kernel - Re: [EXTERNAL] Re: [PATCH hyperv-next] x86/hyperv: Fix APIC ID and VP ID confusion in hv_snp_boot

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Message-ID: <8fa1045a-c3e9-48e0-86fe-ab554d7475c8@linux.microsoft.com>
Date: Fri, 25 Apr 2025 09:43:22 -0700
From: Roman Kisel <romank@...ux.microsoft.com>
To: Saurabh Singh Sengar <ssengar@...rosoft.com>, Wei Liu <wei.liu@...nel.org>
Cc: "bp@...en8.de" <bp@...en8.de>,
 "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
 Dexuan Cui <decui@...rosoft.com>, Haiyang Zhang <haiyangz@...rosoft.com>,
 "hpa@...or.com" <hpa@...or.com>, KY Srinivasan <kys@...rosoft.com>,
 "mikelley@...rosoft.com" <mikelley@...rosoft.com>,
 "mingo@...hat.com" <mingo@...hat.com>,
 "tglx@...utronix.de" <tglx@...utronix.de>,
 Tianyu Lan <Tianyu.Lan@...rosoft.com>,
 "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "x86@...nel.org" <x86@...nel.org>, Allen Pais <apais@...rosoft.com>,
 Ben Hillis <Ben.Hillis@...rosoft.com>,
 Brian Perkins <Brian.Perkins@...rosoft.com>,
 Sunil Muthuswamy <sunilmut@...rosoft.com>
Subject: Re: [EXTERNAL] Re: [PATCH hyperv-next] x86/hyperv: Fix APIC ID and VP
 ID confusion in hv_snp_boot_ap()



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@...r.kernel.org
>>> Fixes: 44676bb9d566 ("x86/hyperv: Add smp support for SEV-SNP guest")
>>> Signed-off-by: Roman Kisel <romank@...ux.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