linux-kernel - Re: [RFC v2 14/17] x86/apic: Add kexec support for Secure AVIC

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Message-ID: <be2c8047-fd68-4858-bb92-bf301d7967b4@amd.com>
Date: Tue, 1 Apr 2025 16:05:22 +0530
From: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
To: Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org
Cc: bp@...en8.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
 Thomas.Lendacky@....com, nikunj@....com, Santosh.Shukla@....com,
 Vasant.Hegde@....com, Suravee.Suthikulpanit@....com, David.Kaplan@....com,
 x86@...nel.org, hpa@...or.com, peterz@...radead.org, seanjc@...gle.com,
 pbonzini@...hat.com, kvm@...r.kernel.org, kirill.shutemov@...ux.intel.com,
 huibo.wang@....com, naveen.rao@....com
Subject: Re: [RFC v2 14/17] x86/apic: Add kexec support for Secure AVIC



On 3/21/2025 9:18 PM, Thomas Gleixner wrote:
> On Wed, Feb 26 2025 at 14:35, Neeraj Upadhyay wrote:
>>  
>> +/*
>> + * Unregister GPA of the Secure AVIC backing page.
>> + *
>> + * @apic_id: APIC ID of the vCPU. Use -1ULL for the current vCPU
> 
> Yes, -1ULL is really a sensible value - NOT. Ever thought about
> signed/unsigned?
> 

In table "Table 7: List of Supported Non-Automatic Events" of GHCB spec [1],
0xffff_ffff_ffff_ffff is used for Secure AVIC GHCB event

"RAX will have the APIC ID of the target vCPU or 0xffff_ffff_ffff_ffff
 for the vCPU doing the call"

I am using -1ULL for that here.



[1] https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/specifications/56421.pdf


>> + *           doing the call.
> 
> How would this function ever make sense to be invoked from a remote CPU?
> 

I will update the interface in next version. Remote CPU interface is not used.

>> + * On success, returns previously registered GPA of the Secure AVIC
>> + * backing page in gpa arg.
> 
> Please use proper kernel-doc formatting and not some made up thing which
> looks like it.
> 

Ok. I will update this.


- Neeraj

> Thanks,
> 
>         tglx