Commit 829157be authored Feb 13, 2008 by H. Peter Anvin Committed by Ingo Molnar Feb 26, 2008

x86: handle BIOSes which terminate e820 with CF=1 and no SMAP



The proper way to terminate the e820 chain is with %ebx == 0 on the
last legitimate memory block.  However, several BIOSes don't do that
and instead return error (CF = 1) when trying to read off the end of
the list.  For this error return, %eax doesn't necessarily return the
SMAP signature -- correctly so, since %ah should contain an error code
in this case.

To deal with some particularly broken BIOSes, we clear the entire e820
chain if the SMAP signature is missing in the middle, indicating a
plain insane e820 implementation.  However, we need to make the test
for CF = 1 before the SMAP check.

This fixes at least one HP laptop (nc6400) for which none of the
memory-probing methods (e820, e801, 88) functioned fully according to
spec.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

parent 4cd20952

arch/x86/boot/memory.c

+6 −3

Original line number	Diff line number	Diff line
		@@ -37,6 +37,12 @@ static int detect_memory_e820(void)
		"=m" (*desc)
		: "D" (desc), "d" (SMAP), "a" (0xe820));

		/* BIOSes which terminate the chain with CF = 1 as opposed
		to %ebx = 0 don't always report the SMAP signature on
		the final, failing, probe. */
		if (err)
		break;

		/* Some BIOSes stop returning SMAP in the middle of
		the search loop. We don't know exactly how the BIOS
		screwed up the map at that point, we might have a
		@@ -47,9 +53,6 @@ static int detect_memory_e820(void)
		break;
		}

		if (err)
		break;

		count++;
		desc++;
		} while (next && count < E820MAX);