linux-kernel - Re: [PATCH v4 04/15] x86/sev: Check for the presence of an SVSM in the SNP Secrets page

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Message-ID: <f8a92b19-9090-40ea-c2cf-707005f583a5@amd.com>
Date: Mon, 20 May 2024 08:57:43 -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 04/15] x86/sev: Check for the presence of an SVSM in
 the SNP Secrets page

On 5/17/24 10:58, Borislav Petkov wrote:
> On Thu, May 02, 2024 at 10:29:02AM -0500, Tom Lendacky wrote:
>> PAGE_ALIGNED and IS_ALIGNED are from two separate header files (mm.h and
>> align.h) which seems like a lot of extra changes for just one check.
> 
> No, pls put them in a single shared/mm.h header. And no, those are not
> a lot of extra changes - those are changes which are moving the code in
> the right direction and we do them sooner rather than later, otherwise
> they'd pile up and we'll never be able to find time to do them - sev.c
> movement attempt case-in-point.

So this will be a new shared directory in the top level include 
directory (as PAGE_ALIGNED is defined in include/linux/mm.h), not just 
in the arch/x86/include directory like the others (io.h, msr.h and 
tdx.h). Is that what you want?

Thanks,
Tom

> 
>> Not sure I agree. I'd prefer to keep the comment here because it is
>> specific to this rmpadjust() call. See below.
> 
> Just don't replicate some versions of the same comment all over the
> place. Do one big comment which explains which RMPADJUST has to do with
> VMPL levels - perhaps over the insn - and then refer to it from the
> other places after adding the specific explanations for them.
> 
>> Right. Not sure about the "cannot", more like "must not." The specification
>> states that the guest should run at a VMPL other than 0. If an SVSM starts
>> the guest at VMPL0, then the SVSM would not be protected from guest.
> 
> Yeah, well, you do terminate the guest if it is running at VMPL 0 *in*
> the presence of a SVSM so it is a "must not". Ok.
>