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HIGHMEM64G support was added in linux-2.3.25 to support (then) high-end Pentium Pro and Pentium III Xeon servers with more than 4GB of addressing, NUMA and PCI-X slots started appearing. I have found no evidence of this ever being used in regular dual-socket servers or consumer devices, all the users seem obsolete these days, even by i386 standards: - Support for NUMA servers (NUMA-Q, IBM x440, unisys) was already removed ten years ago. - 4+ socket non-NUMA servers based on Intel 450GX/450NX, HP F8 and ServerWorks ServerSet/GrandChampion could theoretically still work with 8GB, but these were exceptionally rare even 20 years ago and would have usually been equipped with than the maximum amount of RAM. - Some SKUs of the Celeron D from 2004 had 64-bit mode fused off but could still work in a Socket 775 mainboard designed for the later Core 2 Duo and 8GB. Apparently most BIOSes at the time only allowed 64-bit CPUs. - The rare Xeon LV "Sossaman" came on a few motherboards with registered DDR2 memory support up to 16GB. - In the early days of x86-64 hardware, there was sometimes the need to run a 32-bit kernel to work around bugs in the hardware drivers, or in the syscall emulation for 32-bit userspace. This likely still works but there should never be a need for this any more. PAE mode is still required to get access to the 'NX' bit on Atom 'Pentium M' and 'Core Duo' CPUs. Signed-off-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: https://lore.kernel.org/r/20250226213714.4040853-6-arnd@kernel.org
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42 lines
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.. SPDX-License-Identifier: GPL-2.0
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==================
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USB Legacy support
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==================
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:Author: Vojtech Pavlik <vojtech@suse.cz>, January 2004
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Also known as "USB Keyboard" or "USB Mouse support" in the BIOS Setup is a
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feature that allows one to use the USB mouse and keyboard as if they were
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their classic PS/2 counterparts. This means one can use an USB keyboard to
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type in LILO for example.
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It has several drawbacks, though:
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1) On some machines, the emulated PS/2 mouse takes over even when no USB
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mouse is present and a real PS/2 mouse is present. In that case the extra
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features (wheel, extra buttons, touchpad mode) of the real PS/2 mouse may
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not be available.
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2) If AMD64 64-bit mode is enabled, again system crashes often happen,
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because the SMM BIOS isn't expecting the CPU to be in 64-bit mode. The
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BIOS manufacturers only test with Windows, and Windows doesn't do 64-bit
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yet.
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Solutions:
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Problem 1)
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can be solved by loading the USB drivers prior to loading the
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PS/2 mouse driver. Since the PS/2 mouse driver is in 2.6 compiled into
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the kernel unconditionally, this means the USB drivers need to be
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compiled-in, too.
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Problem 2)
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is usually fixed by a BIOS update. Check the board
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manufacturers web site. If an update is not available, disable USB
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Legacy support in the BIOS. If this alone doesn't help, try also adding
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idle=poll on the kernel command line. The BIOS may be entering the SMM
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on the HLT instruction as well.
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