linux-kernel - Re: [PATCH v3 02/14] x86/sev: Make the VMPL0 checking function more generic

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Date: Wed, 17 Apr 2024 22:50:48 +0200
From: Borislav Petkov <bp@...en8.de>
To: Tom Lendacky <thomas.lendacky@....com>
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 v3 02/14] x86/sev: Make the VMPL0 checking function more
 generic

On Wed, Apr 17, 2024 at 03:35:53PM -0500, Tom Lendacky wrote:
> Well, it doesn't really modify any permissions that matter. It tries to
> change the permission of a lesser privileged VMPL level.

Potato potato. :-P

> Since the kernel only runs at a single VMPL it would never be
> effected. The operation performed here is to update VMPL1 permission
> levels (which can only be done successfully at VMPL0) and return the
> result of the operation.  A success implies running at VMPL0 and
> failure implies not running at VMPL0.

Yap.

The point is, it is calling RMPADJUST. And it does modify RMP
permissions of a guest page.

Thus, if you prefer, you can go all out and call the helper

	rmp_adjust_permissions(unsigned int tgt_vmpl, void *pa)

and make it generic from the get-go.

And then have the macro wrap around it in order to explain that
particular use with the macro name.

If it is still not clear what I mean, lemme know and I'll do a diff
ontop.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette