path: root/arch/x86/boot/memory.c
diff options
authorH. Peter Anvin <hpa@zytor.com>2008-02-13 11:16:46 -0800
committerIngo Molnar <mingo@elte.hu>2008-02-26 12:55:52 +0100
commit829157be590af1c2555fb74c3c4db3327e3201fc (patch)
tree75f4744449a9a06dd1186215cb2d6d5ab7235798 /arch/x86/boot/memory.c
parent4cd20952d74323df06e438c0c3273b5be89d6bfd (diff)
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>
Diffstat (limited to 'arch/x86/boot/memory.c')
1 files changed, 6 insertions, 3 deletions
diff --git a/arch/x86/boot/memory.c b/arch/x86/boot/memory.c
index 378353956b5d..e77d89f9e8aa 100644
--- a/arch/x86/boot/memory.c
+++ b/arch/x86/boot/memory.c
@@ -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)
- if (err)
- break;
} while (next && count < E820MAX);