linux-kernel - Re: [PATCH v4 10/15] virt: sev-guest: Choose the VMPCK key based on executing VMPL

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Date: Fri, 31 May 2024 14:34:37 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: Borislav Petkov <bp@...en8.de>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org, linux-coco@...ts.linux.dev,
 svsm-devel@...onut-svsm.dev, Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>,
 "H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>,
 Dan Williams <dan.j.williams@...el.com>, Michael Roth
 <michael.roth@....com>, Ashish Kalra <ashish.kalra@....com>
Subject: Re: [PATCH v4 10/15] virt: sev-guest: Choose the VMPCK key based on
 executing VMPL

On 5/31/24 14:03, Borislav Petkov wrote:
> On Fri, May 31, 2024 at 01:36:06PM -0500, Tom Lendacky wrote:
>> The sev-guest driver needs to access it. Given it is a driver/module, I
>> created the accessor rather than mark the variable EXPORT_SYMBOL_GPL(). Your
>> call, I'm fine with either.
> 
> Yeah, if the variable doesn't change after init, then you don't really
> need an accessor.
> 
>> Yes, the driver can and does figure it out. However, this module parameter
>> was added in the off chance the default VMPCK gets wiped. Then you can
>> reload the driver and use a different (less privileged) VMPCK.
> 
> Is that what the text over snp_disable_vmpck() is alluding to?

Yes, I believe so.

> 
> Or where are we documenting this intended use?

It probably should have been documented above the module parameter itself 
and/or in the sev-guest documentation. Those can be done as part of this 
patch or separate, whichever is preferred.

Thanks,
Tom

> 
> Thx.
>