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 13:46:58 +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 Mon, Mar 25, 2024 at 05:26:21PM -0500, Tom Lendacky wrote:
> -static void enforce_vmpl0(void)
> +static bool running_at_vmpl0(void *va)

Not too crazy about it: you're turning it into a function which runs in
boolean context but takes a void *?!

And the boolean result is only a side-effect or what it does to the
argument - modify its permissions. Which is weird and not really
obvious.

I'd prefer it if you made it into

static void vmpl0_modify_permissions(void *va)

which basically says, modify the permissions of @va in vmpl0, which is
a lot closer to what the function does.

And then do

#define running_at_vmpl0(va)	vmpl0_modify_permissions((va))

because then through the indirection is at least clear how that "am
I running at VMPL0?" check is being done.

And later, if we need other VMPLs, we can extend
vmpl0_modify_permissions() and even do a more generic

vmpl_modify_permissions(unsigned int vmpl_level, void *va)

and so on and kill the silly macro.

Thx.

-- 
Regards/Gruss,
    Boris.

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