linux-kernel - Re: [PATCH 05/29] x86/boot/e820: Print gaps in the E820 table

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Message-ID: <aAc6aj5FVMkwDo06@surfacebook.localdomain>
Date: Tue, 22 Apr 2025 09:42:50 +0300
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Ingo Molnar <mingo@...nel.org>
Cc: linux-kernel@...r.kernel.org, Andy Shevchenko <andy@...nel.org>,
	Arnd Bergmann <arnd@...nel.org>, Borislav Petkov <bp@...en8.de>,
	Juergen Gross <jgross@...e.com>, "H . Peter Anvin" <hpa@...or.com>,
	Kees Cook <keescook@...omium.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mike Rapoport <rppt@...nel.org>,
	Paul Menzel <pmenzel@...gen.mpg.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	David Woodhouse <dwmw@...zon.co.uk>
Subject: Re: [PATCH 05/29] x86/boot/e820: Print gaps in the E820 table

Mon, Apr 21, 2025 at 08:51:45PM +0200, Ingo Molnar kirjoitti:
> Gaps in the E820 table are not obvious at a glance and can
> easily be overlooked.
> 
> Print out gaps in the E820 table:
> 
> Before:
> 
> 	BIOS-provided physical RAM map:
> 	BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff] usable
> 	BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] reserved
> 	BIOS-e820: [mem 0x00000000000f0000-0x00000000000fffff] reserved
> 	BIOS-e820: [mem 0x0000000000100000-0x000000007ffdbfff] usable
> 	BIOS-e820: [mem 0x000000007ffdc000-0x000000007fffffff] reserved
> 	BIOS-e820: [mem 0x00000000b0000000-0x00000000bfffffff] reserved
> 	BIOS-e820: [mem 0x00000000fed1c000-0x00000000fed1ffff] reserved
> 	BIOS-e820: [mem 0x00000000feffc000-0x00000000feffffff] reserved
> 	BIOS-e820: [mem 0x00000000fffc0000-0x00000000ffffffff] reserved
> 	BIOS-e820: [mem 0x000000fd00000000-0x000000ffffffffff] reserved
> After:
> 
> 	BIOS-provided physical RAM map:
> 	BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff] usable
> 	BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] reserved
> 	BIOS-e820: [gap 0x00000000000a0000-0x00000000000effff]
> 	BIOS-e820: [mem 0x00000000000f0000-0x00000000000fffff] reserved
> 	BIOS-e820: [mem 0x0000000000100000-0x000000007ffdbfff] usable
> 	BIOS-e820: [mem 0x000000007ffdc000-0x000000007fffffff] reserved
> 	BIOS-e820: [gap 0x0000000080000000-0x00000000afffffff]
> 	BIOS-e820: [mem 0x00000000b0000000-0x00000000bfffffff] reserved
> 	BIOS-e820: [gap 0x00000000c0000000-0x00000000fed1bfff]
> 	BIOS-e820: [mem 0x00000000fed1c000-0x00000000fed1ffff] reserved
> 	BIOS-e820: [gap 0x00000000fed20000-0x00000000feffbfff]
> 	BIOS-e820: [mem 0x00000000feffc000-0x00000000feffffff] reserved
> 	BIOS-e820: [gap 0x00000000ff000000-0x00000000fffbffff]
> 	BIOS-e820: [mem 0x00000000fffc0000-0x00000000ffffffff] reserved
> 	BIOS-e820: [gap 0x0000000100000000-0x000000fcffffffff]
> 	BIOS-e820: [mem 0x000000fd00000000-0x000000ffffffffff] reserved
> 
> Also warn about badly ordered E820 table entries:
> 
> 	BUG: out of order E820 entry!
> 
> ( this is printed before the entry is printed, so there's no need to
>   print any additional data with the warning. )

...

> +		u64 range_start, range_end;

struct range (from range.h) and...

> +		range_start = entry->addr;
> +		range_end   = entry->addr + entry->size;
>  
> +		/* Out of order E820 maps should not happen: */
> +		if (range_start < range_end_prev)
> +			pr_info("BUG: out of order E820 entry!\n");
> +
> +		if (range_start > range_end_prev) {
> +			pr_info("%s: [gap %#018Lx-%#018Lx]\n",
> +				who,
> +				range_end_prev,
> +				range_start-1);

%pra
with who mentioned the "gap"?

> +		}

-- 
With Best Regards,
Andy Shevchenko