Re: [PATCHv2 0/4] x86: 5-level related changes into decompression code

[Joe Perches]

On Thu, 2017-11-30 at 10:31 +0300, Kirill A. Shutemov wrote:
> On Wed, Nov 29, 2017 at 05:48:51PM +0000, Borislav Petkov wrote:
> > On Wed, Nov 29, 2017 at 08:08:31PM +0300, Kirill A. Shutemov wrote:
> > > We're really early in the boot -- startup_64 in decompression code -- and
> > > I don't know a way print a message there. Is there a way?
> > > 
> > > no_longmode handled by just hanging the machine. Is it enough for no_la57
> > > case too?
> > 
> > Patch pls.
> 
> The patch below on top of patch 2/4 from this patch would do the trick.
> 
> Please give it a shot.
> 
> From 95b5489d1f4ea03c6226d13eb6797825234489d6 Mon Sep 17 00:00:00 2001
> From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> Date: Thu, 30 Nov 2017 10:23:53 +0300
> Subject: [PATCH] x86/boot/compressed/64: Print error if 5-level paging is not
>  supported
> 
> We cannot proceed booting if the machine doesn't support the paging mode
> kernel was compiled for.
> 
> Getting error the usual way -- via validate_cpu() -- is not going to
> work. We need to enable appropriate paging mode before that, otherwise
> kernel would triple-fault during KASLR setup.
> 
> This code will go away once we get support for boot-time switching
> between paging modes.

trivia:

> diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
[]
> @@ -362,6 +364,13 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
>  	console_init();
>  	debug_putstr("early console in extract_kernel\n");
>  
> +	if (IS_ENABLED(CONFIG_X86_5LEVEL) && !l5_paging_required()) {
> +		error("The kernel is compiled with 5-level paging enabled, "
> +				"but the CPU doesn't support la57\n"

la57 is lanthanum, perhaps something less obscure or more
readily searchable?  Maybe cr4.la57?  it?

Maybe something like:

"This linux kernel as configured requires 5-level paging\n"
"This CPU does not support the required 'cr4.la57' feature\n"
"Unable to boot - please use a kernel appropriate for your CPU\n"

And please use complete coalesced single lines.

> +				"Unable to boot - please use "
> +				"a kernel appropriate for your CPU.\n");

Here too.  Thanks.