Re: [PATCH AUTOSEL 5.2 51/76] x86/boot/compressed/64: Fix boot on machines with broken E820 table

Kirill A. Shutemov
2019-08-29T22:17:23Z

On Thu, Aug 29, 2019 at 02:12:46PM -0400, Sasha Levin wrote:
> From: "Kirill A. Shutemov" <kirill@shutemov.name>
>
> [ Upstream commit 0a46fff2f9108c2c44218380a43a736cf4612541 ]
>
> BIOS on Samsung 500C Chromebook reports very rudimentary E820 table that
> consists of 2 entries:
>
> BIOS-e820: [mem 0x0000000000000000-0x0000000000000fff] usable
> BIOS-e820: [mem 0x00000000fffff000-0x00000000ffffffff] reserved
>
> It breaks logic in find_trampoline_placement(): bios_start lands on the
> end of the first 4k page and trampoline start gets placed below 0.
>
> Detect underflow and don't touch bios_start for such cases. It makes
> kernel ignore E820 table on machines that doesn't have two usable pages
> below BIOS_START_MAX.
>
> Fixes: 1b3a62643660 ("x86/boot/compressed/64: Validate trampoline placement against E820")
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Signed-off-by: Borislav Petkov <bp@suse.de>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: x86-ml <x86@kernel.org>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=203463
> Link: https://lkml.kernel.org/r/20190813131654.24378-1-kirill.shutemov@linux.intel.com
> Signed-off-by: Sasha Levin <sashal@kernel.org>

Please postpone backporting the patch (and into other trees). There's a
fixup for it:

http://lore.kernel.org/r/20190826133326.7cxb4vbmiawffv2r@box

--
Kirill A. Shutemov