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Message-ID: <aAc83YZ8K08HYoyP@kernel.org>
Date: Tue, 22 Apr 2025 09:53:17 +0300
From: Mike Rapoport <rppt@...nel.org>
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>,
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 07/29] x86/boot/e820: Print out sizes of E820 memory
ranges
On Mon, Apr 21, 2025 at 08:51:47PM +0200, Ingo Molnar wrote:
> 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] 639 KB kernel usable RAM
> BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] 1 KB reserved
> BIOS-e820: [gap 0x00000000000a0000-0x00000000000effff] 320 KB ...
> BIOS-e820: [mem 0x00000000000f0000-0x00000000000fffff] 64 KB reserved
> BIOS-e820: [mem 0x0000000000100000-0x000000007ffdbfff] 1.9 GB kernel usable RAM
> BIOS-e820: [mem 0x000000007ffdc000-0x000000007fffffff] 144 KB reserved
> BIOS-e820: [gap 0x0000000080000000-0x00000000afffffff] 768 MB ...
> BIOS-e820: [mem 0x00000000b0000000-0x00000000bfffffff] 256 MB reserved
> BIOS-e820: [gap 0x00000000c0000000-0x00000000fed1bfff] 1005.1 MB ...
> BIOS-e820: [mem 0x00000000fed1c000-0x00000000fed1ffff] 16 KB reserved
> BIOS-e820: [gap 0x00000000fed20000-0x00000000feffbfff] 2.8 MB ...
> BIOS-e820: [mem 0x00000000feffc000-0x00000000feffffff] 16 KB reserved
> BIOS-e820: [gap 0x00000000ff000000-0x00000000fffbffff] 15.7 MB ...
> BIOS-e820: [mem 0x00000000fffc0000-0x00000000ffffffff] 256 KB reserved
> BIOS-e820: [gap 0x0000000100000000-0x000000fcffffffff] 1008 GB ...
> BIOS-e820: [mem 0x000000fd00000000-0x000000ffffffffff] 12 GB reserved
>
> Note how a 1-digit precision field is printed out if a range is
> fractional in its largest-enclosing natural size unit.
>
> So the "256 MB" and "12 GB" fields above denote exactly 256 MB and
> 12 GB regions, while "1.9 GB" signals the region's fractional nature
> and it being just below 2GB.
>
> Printing E820 maps with such details visualizes 'weird' ranges
> at a glance, and gives users a better understanding of how
> large the various ranges are, without having to perform hexadecimal
> subtraction in their minds.
>
> Signed-off-by: Ingo Molnar <mingo@...nel.org>
> Cc: Andy Shevchenko <andy@...nel.org>
> Cc: Arnd Bergmann <arnd@...nel.org>
> Cc: David Woodhouse <dwmw@...zon.co.uk>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Mike Rapoport (Microsoft) <rppt@...nel.org>
> (cherry picked from commit d1ac6b8718575a7ea2f0a1ff347835a8879df673)
> ---
> arch/x86/kernel/e820.c | 47 +++++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 45 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
> index 10bd10bd5672..8ee89962fcbf 100644
> --- a/arch/x86/kernel/e820.c
> +++ b/arch/x86/kernel/e820.c
> @@ -199,6 +199,41 @@ static void __init e820_print_type(enum e820_type type)
> }
> }
>
> +/*
> + * Print out the size of a E820 region, in human-readable
> + * fashion, going from KB, MB, GB to TB units.
> + *
> + * Print out fractional sizes with a single digit of precision.
> + */
> +static void e820_print_size(u64 size)
> +{
> + if (size < SZ_1M) {
> + if (size & (SZ_1K-1))
> + pr_cont(" %4llu.%01llu KB", size/SZ_1K, 10*(size & (SZ_1K-1))/SZ_1K);
> + else
> + pr_cont(" %4llu KB", size/SZ_1K);
> + return;
> + }
I'd make this a helper, e.g
static void __e820_print_size(u64 size, u64 unit, const char *unit_name)
{
if (size & (unit - 1)) {
u64 fraction = 10 * (size & (unit - 1))/unit;
pr_cont(" %4llu.%01llu %s", size/unit, fraction, unit_name);
} else {
pr_cont(" %4llu %s", size/unit, unit_name);
}
}
> + if (size < SZ_1G) {
> + if (size & (SZ_1M-1))
> + pr_cont(" %4llu.%01llu MB", size/SZ_1M, 10*(size & (SZ_1M-1))/SZ_1M);
> + else
> + pr_cont(" %4llu MB", size/SZ_1M);
> + return;
> + }
> + if (size < SZ_1T) {
> + if (size & (SZ_1G-1))
> + pr_cont(" %4llu.%01llu GB", size/SZ_1G, 10*(size & (SZ_1G-1))/SZ_1G);
> + else
> + pr_cont(" %4llu GB", size/SZ_1G);
> + return;
> + }
> + if (size & (SZ_1T-1))
> + pr_cont(" %4llu.%01llu TB", size/SZ_1T, 10*(size & (SZ_1T-1))/SZ_1T);
> + else
> + pr_cont(" %4llu TB", size/SZ_1T);
> +}
> +
> static void __init e820__print_table(const char *who)
> {
> u64 range_end_prev = 0;
> @@ -215,14 +250,22 @@ static void __init e820__print_table(const char *who)
> if (range_start < range_end_prev)
> pr_info("BUG: out of order E820 entry!\n");
>
> + /* Print gaps, if any: */
> if (range_start > range_end_prev) {
> - pr_info("%s: [gap %#018Lx-%#018Lx]\n",
> + u64 gap_size = range_start - range_end_prev;
> +
> + pr_info("%s: [gap %#018Lx-%#018Lx]",
> who,
> range_end_prev,
> range_start-1);
> +
> + e820_print_size(gap_size);
> + pr_cont(" ...\n");
> }
>
> - pr_info("%s: [mem %#018Lx-%#018Lx] ", who, range_start, range_end-1);
> + /* Print allocated ranges: */
> + pr_info("%s: [mem %#018Lx-%#018Lx]", who, range_start, range_end-1);
> + e820_print_size(entry->size);
> e820_print_type(entry->type);
> pr_cont("\n");
>
> --
> 2.45.2
>
--
Sincerely yours,
Mike.
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