| From 7c10093692ed2e6f318387d96b829320aa0ca64c Mon Sep 17 00:00:00 2001 |
| From: "H. Peter Anvin" <hpa@linux.intel.com> |
| Date: Wed, 27 Feb 2013 12:46:40 -0800 |
| Subject: x86: Make sure we can boot in the case the BDA contains pure garbage |
| |
| From: "H. Peter Anvin" <hpa@linux.intel.com> |
| |
| commit 7c10093692ed2e6f318387d96b829320aa0ca64c upstream. |
| |
| On non-BIOS platforms it is possible that the BIOS data area contains |
| garbage instead of being zeroed or something equivalent (firmware |
| people: we are talking of 1.5K here, so please do the sane thing.) |
| |
| We need on the order of 20-30K of low memory in order to boot, which |
| may grow up to < 64K in the future. We probably want to avoid the |
| lowest of the low memory. At the same time, it seems extremely |
| unlikely that a legitimate EBDA would ever reach down to the 128K |
| (which would require it to be over half a megabyte in size.) Thus, |
| pick 128K as the cutoff for "this is insane, ignore." We may still |
| end up reserving a bunch of extra memory on the low megabyte, but that |
| is not really a major issue these days. In the worst case we lose |
| 512K of RAM. |
| |
| This code really should be merged with trim_bios_range() in |
| arch/x86/kernel/setup.c, but that is a bigger patch for a later merge |
| window. |
| |
| Reported-by: Darren Hart <dvhart@linux.intel.com> |
| Signed-off-by: H. Peter Anvin <hpa@linux.intel.com> |
| Cc: Matt Fleming <matt.fleming@intel.com> |
| Link: http://lkml.kernel.org/n/tip-oebml055yyfm8yxmria09rja@git.kernel.org |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| arch/x86/kernel/head.c | 57 ++++++++++++++++++++++++++++++------------------- |
| 1 file changed, 36 insertions(+), 21 deletions(-) |
| |
| --- a/arch/x86/kernel/head.c |
| +++ b/arch/x86/kernel/head.c |
| @@ -5,8 +5,6 @@ |
| #include <asm/setup.h> |
| #include <asm/bios_ebda.h> |
| |
| -#define BIOS_LOWMEM_KILOBYTES 0x413 |
| - |
| /* |
| * The BIOS places the EBDA/XBDA at the top of conventional |
| * memory, and usually decreases the reported amount of |
| @@ -16,17 +14,30 @@ |
| * chipset: reserve a page before VGA to prevent PCI prefetch |
| * into it (errata #56). Usually the page is reserved anyways, |
| * unless you have no PS/2 mouse plugged in. |
| + * |
| + * This functions is deliberately very conservative. Losing |
| + * memory in the bottom megabyte is rarely a problem, as long |
| + * as we have enough memory to install the trampoline. Using |
| + * memory that is in use by the BIOS or by some DMA device |
| + * the BIOS didn't shut down *is* a big problem. |
| */ |
| + |
| +#define BIOS_LOWMEM_KILOBYTES 0x413 |
| +#define LOWMEM_CAP 0x9f000U /* Absolute maximum */ |
| +#define INSANE_CUTOFF 0x20000U /* Less than this = insane */ |
| + |
| void __init reserve_ebda_region(void) |
| { |
| unsigned int lowmem, ebda_addr; |
| |
| - /* To determine the position of the EBDA and the */ |
| - /* end of conventional memory, we need to look at */ |
| - /* the BIOS data area. In a paravirtual environment */ |
| - /* that area is absent. We'll just have to assume */ |
| - /* that the paravirt case can handle memory setup */ |
| - /* correctly, without our help. */ |
| + /* |
| + * To determine the position of the EBDA and the |
| + * end of conventional memory, we need to look at |
| + * the BIOS data area. In a paravirtual environment |
| + * that area is absent. We'll just have to assume |
| + * that the paravirt case can handle memory setup |
| + * correctly, without our help. |
| + */ |
| if (paravirt_enabled()) |
| return; |
| |
| @@ -37,19 +48,23 @@ void __init reserve_ebda_region(void) |
| /* start of EBDA area */ |
| ebda_addr = get_bios_ebda(); |
| |
| - /* Fixup: bios puts an EBDA in the top 64K segment */ |
| - /* of conventional memory, but does not adjust lowmem. */ |
| - if ((lowmem - ebda_addr) <= 0x10000) |
| - lowmem = ebda_addr; |
| - |
| - /* Fixup: bios does not report an EBDA at all. */ |
| - /* Some old Dells seem to need 4k anyhow (bugzilla 2990) */ |
| - if ((ebda_addr == 0) && (lowmem >= 0x9f000)) |
| - lowmem = 0x9f000; |
| - |
| - /* Paranoia: should never happen, but... */ |
| - if ((lowmem == 0) || (lowmem >= 0x100000)) |
| - lowmem = 0x9f000; |
| + /* |
| + * Note: some old Dells seem to need 4k EBDA without |
| + * reporting so, so just consider the memory above 0x9f000 |
| + * to be off limits (bugzilla 2990). |
| + */ |
| + |
| + /* If the EBDA address is below 128K, assume it is bogus */ |
| + if (ebda_addr < INSANE_CUTOFF) |
| + ebda_addr = LOWMEM_CAP; |
| + |
| + /* If lowmem is less than 128K, assume it is bogus */ |
| + if (lowmem < INSANE_CUTOFF) |
| + lowmem = LOWMEM_CAP; |
| + |
| + /* Use the lower of the lowmem and EBDA markers as the cutoff */ |
| + lowmem = min(lowmem, ebda_addr); |
| + lowmem = min(lowmem, LOWMEM_CAP); /* Absolute cap */ |
| |
| /* reserve all memory between lowmem and the 1MB mark */ |
| memblock_reserve(lowmem, 0x100000 - lowmem); |