[Bug 209821] UEFI - installation media hangs when booting on ASUS P6P67 DELUXE

From: <bugzilla-noreply_at_freebsd.org>
Date: Fri, 07 Jan 2022 16:56:13 UTC

--- Comment #66 from David Sebek <dasebek@gmail.com> ---
(In reply to Dani from comment #65)
I think there were two reasons why UEFI boot froze on some systems. Before the
changes in 13-STABLE and 14-CURRENT, the kernel needed to be loaded to a
specific physical memory location. Copying the kernel to a specific location in
memory could cause problems:

1. The target location could contain the boot loader code. When the boot loader
was copying the kernel to the expected address in memory, it accidentally
overwrote the boot loader’s code that was responsible for the copy operation,
which resulted in a freeze of the system.

2. The target location could contain hardware-reserved addresses. Copying the
kernel over those memory addresses could freeze the system.

The patch from #41 fixes only the problem (1.) by not using the boot loader
code that may get overwritten.

FreeBSD 14-CURRENT and 13-STABLE fix both problems (1.) and (2.) by not
requiring the kernel to be copied to a specific memory address.

The patch #41 needed some minor modifications in order to be applied to FreeBSD
12. I can take a look at it and update for FreeBSD 12.

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