From 9d4b9b80e91bda354b4779ab16c02f26f1d56ae0 Mon Sep 17 00:00:00 2001 From: "H. Peter Anvin" Date: Thu, 21 May 2009 11:46:16 -0700 Subject: [PATCH] x86, setup: revert ACPI 3 E820 extended attributes support Remove ACPI 3 E820 extended memory attributes support. At least one vendor actively set all the flags to zero, but left ECX on return at 24. This bug may be present in other BIOSes. The breakage functionally means the ACPI 3 flags are probably completely useless, and that no OS any time soon is going to rely on their existence. Therefore, drop support completely. We may want to revisit this question in the future, if we find ourselves actually needing the flags. This reverts all or part of the following checkins: 273ff27b9863c0dabed8851597f4e58e914374d8 8b7e5c33a7266eb84db0648a63760c5acc839f85 However, retain the part from the latter commit that copies e820 into a temporary buffer; that is an unrelated BIOS workaround. Put in a comment to explain that part. See https://bugzilla.redhat.com/show_bug.cgi?id=499396 for some additional information. [ Impact: detect all memory on affected machines ] Reported-by: Thomas J. Baker Signed-off-by: H. Peter Anvin Acked-by: Len Brown Cc: Chuck Ebbert Cc: Kyle McMartin Cc: Matt Domsch --- arch/x86/boot/memory.c | 29 +++++++++++++---------------- 1 file changed, 13 insertions(+), 16 deletions(-) diff --git a/arch/x86/boot/memory.c b/arch/x86/boot/memory.c index 5054c2ddd1a03..74b3d2ba84e90 100644 --- a/arch/x86/boot/memory.c +++ b/arch/x86/boot/memory.c @@ -17,11 +17,6 @@ #define SMAP 0x534d4150 /* ASCII "SMAP" */ -struct e820_ext_entry { - struct e820entry std; - u32 ext_flags; -} __attribute__((packed)); - static int detect_memory_e820(void) { int count = 0; @@ -29,13 +24,21 @@ static int detect_memory_e820(void) u32 size, id, edi; u8 err; struct e820entry *desc = boot_params.e820_map; - static struct e820_ext_entry buf; /* static so it is zeroed */ + static struct e820entry buf; /* static so it is zeroed */ /* - * Set this here so that if the BIOS doesn't change this field - * but still doesn't change %ecx, we're still okay... + * Note: at least one BIOS is known which assumes that the + * buffer pointed to by one e820 call is the same one as + * the previous call, and only changes modified fields. Therefore, + * we use a temporary buffer and copy the results entry by entry. + * + * This routine deliberately does not try to account for + * ACPI 3+ extended attributes. This is because there are + * BIOSes in the field which report zero for the valid bit for + * all ranges, and we don't currently make any use of the + * other attribute bits. Revisit this if we see the extended + * attribute bits deployed in a meaningful way in the future. */ - buf.ext_flags = 1; do { size = sizeof buf; @@ -66,13 +69,7 @@ static int detect_memory_e820(void) break; } - /* ACPI 3.0 added the extended flags support. If bit 0 - in the extended flags is zero, we're supposed to simply - ignore the entry -- a backwards incompatible change! */ - if (size > 20 && !(buf.ext_flags & 1)) - continue; - - *desc++ = buf.std; + *desc++ = buf; count++; } while (next && count < ARRAY_SIZE(boot_params.e820_map)); -- 2.39.5