linux-kernel - Re: [RFC 01/14] x86/apic: Add new driver for Secure AVIC

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Message-ID: <6b2d9a59-cfca-4d6c-915b-ca36826ce96b@amd.com>
Date: Thu, 21 Nov 2024 13:33:29 +0530
From: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
To: Borislav Petkov <bp@...en8.de>
Cc: "Melody (Huibo) Wang" <huibo.wang@....com>, linux-kernel@...r.kernel.org,
 tglx@...utronix.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
Subject: Re: [RFC 01/14] x86/apic: Add new driver for Secure AVIC



On 11/21/2024 11:11 AM, Borislav Petkov wrote:
> On Thu, Nov 21, 2024 at 10:35:35AM +0530, Neeraj Upadhyay wrote:
>> APIC common code (arch/x86/kernel/apic/apic.c) and other parts of the
>> x86 code use X86_X2APIC config to enable x2apic related initialization
>> and functionality. So, dependency on X2APIC need to be there.
> 
> Have you actually tried to remove the dependency and see how it looks?
> 

No, I didn't try it previously, as based on checking the code below
is what I understand how the code is layered:

- Common x2APIC code in arch/x86/... initializes the x2APIC
  architecture sequence and other parts of common x2apic initialization:

  * Disable and enable x2apic (...kernel/apic/apic.c).
  * max_apicid setting in (...kernel/apic/init.c)
  * acpi_parse_x2apic() registration of APIC ID in early
    topo maps (kernel/acpi/boot.c)
  * Enable x2apic in startup code (...kernel/head_64.S).
  

- Each x2apic driver in arch/x86/kernel/apic provides callbacks for implementation
  specific (x2apic_uv_x.c, apic_numachip.c) or a particular mode
  specific (x2apic_phys.c, x2apic_cluster.c) functionality.

As SAVIC's guest APIC register accesses match x2avic (which uses x2APIC MSR
interface in guest), the x2apic common flow need to be executed in the
guest.


- Neeraj

> Thx.
>