linux-kernel - Re: [PATCH v16 8/8] x86/smpboot: Allow parallel bringup for SEV-ES

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Date:   Thu, 23 Mar 2023 13:28:38 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     "Woodhouse, David" <dwmw@...zon.co.uk>,
        "usama.arif@...edance.com" <usama.arif@...edance.com>,
        "bp@...en8.de" <bp@...en8.de>
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        "brgerst@...il.com" <brgerst@...il.com>,
        "arjan@...ux.intel.com" <arjan@...ux.intel.com>,
        "hewenliang4@...wei.com" <hewenliang4@...wei.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "simon.evans@...edance.com" <simon.evans@...edance.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
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        "oleksandr@...alenko.name" <oleksandr@...alenko.name>,
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        "Rapan, Sabin" <sabrapan@...zon.com>,
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        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH v16 8/8] x86/smpboot: Allow parallel bringup for SEV-ES

On 3/23/23 10:34, Woodhouse, David wrote:
> On Thu, 2023-03-23 at 08:16 -0500, Tom Lendacky wrote:
>>
>> Maybe call this sev_early_get_cpuid_0b() or such to imply that the MSR
>> protocol is being used and only retrieving / returning edx.
> 
> Or indeed sev_early_get_apicid() since that's what it's actually doing,
> and the caller doesn't care *how*.

Sounds good.

> 
>> Also, since it is a function now and can be used at any point, the current
>> GHCB MSR should be saved on entry and restored on exit.
> 
> Well, I don't know that it should be callable at any point. This is
> only supposed to be called from head_64.S.

I agree. But once it's there, someone somewhere in the future may look and 
go, oh, I can call this. So I think it either needs a nice comment above 
it about how it is currently used/called and what to do if it needs to be 
called from someplace other than head_64.S or the MSR needs to be 
saved/restored.

Thanks,
Tom

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