[PATCH] x86_64: Avoid EBDA area in early boot allocator

Based on analysis&patch from Robert Hentosch

Observed on a Dell PE6850 with 16GB

The problem occurs very early on, when the kernel allocates space for the
temporary memory map called bootmap. The bootmap overlaps the EBDA region.
EBDA region is not historically reserved in the e820 mapping. When the
bootmap is freed it marks the EBDA region as usable.

If you notice in setup.c there is already code to work around the EBDA
in reserve_ebda_region(), this check however occurs after the bootmap
is allocated and doesn't prevent the bootmap from using this range.

AK: I redid the original patch. Thanks also to Jan Beulich for
spotting some mistakes.

Cc: Robert_Hentosch@dell.com
Cc: jbeulich@novell.com
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/arch/x86_64/kernel/e820.c b/arch/x86_64/kernel/e820.c
index 62776c07cff15deec7f772096ddf51693ba2303e..222b5b46d2b2df6546ab01e67be1d1b92d713667 100644 (file)
--- a/arch/x86_64/kernel/e820.c
+++ b/arch/x86_64/kernel/e820.c
@@ -76,6 +76,12 @@ static inline int bad_addr(unsigned long *addrp, unsigned long size)
                *addrp = __pa_symbol(&_end);
                return 1;
        }
+
+       if (last >= ebda_addr && addr < ebda_addr + ebda_size) {
+               *addrp = ebda_addr + ebda_size;
+               return 1;
+       }
+
        /* XXX ramdisk image here? */ 
        return 0;
 } 

diff --git a/arch/x86_64/kernel/setup.c b/arch/x86_64/kernel/setup.c
index ebc3c33b1c6c9a940fe47feb78f7b425255393ec..f0870bef24d114b521f625952b79e973ed2a5e1c 100644 (file)
--- a/arch/x86_64/kernel/setup.c
+++ b/arch/x86_64/kernel/setup.c
@@ -571,17 +571,28 @@ static inline void copy_edd(void)
 #endif
 
 #define EBDA_ADDR_POINTER 0x40E
-static void __init reserve_ebda_region(void)
+
+unsigned __initdata ebda_addr;
+unsigned __initdata ebda_size;
+
+static void discover_ebda(void)
 {
-       unsigned int addr;
-       /** 
+       /*
         * there is a real-mode segmented pointer pointing to the 
         * 4K EBDA area at 0x40E
         */
-       addr = *(unsigned short *)phys_to_virt(EBDA_ADDR_POINTER);
-       addr <<= 4;
-       if (addr)
-               reserve_bootmem_generic(addr, PAGE_SIZE);
+       ebda_addr = *(unsigned short *)EBDA_ADDR_POINTER;
+       ebda_addr <<= 4;
+
+       ebda_size = *(unsigned short *)(unsigned long)ebda_addr;
+
+       /* Round EBDA up to pages */
+       if (ebda_size == 0)
+               ebda_size = 1;
+       ebda_size <<= 10;
+       ebda_size = round_up(ebda_size + (ebda_addr & ~PAGE_MASK), PAGE_SIZE);
+       if (ebda_size > 64*1024)
+               ebda_size = 64*1024;
 }
 
 void __init setup_arch(char **cmdline_p)
@@ -627,6 +638,8 @@ void __init setup_arch(char **cmdline_p)
 
        check_efer();
 
+       discover_ebda();
+
        init_memory_mapping(0, (end_pfn_map << PAGE_SHIFT));
 
        dmi_scan_machine();
@@ -669,7 +682,8 @@ void __init setup_arch(char **cmdline_p)
        reserve_bootmem_generic(0, PAGE_SIZE);
 
        /* reserve ebda region */
-       reserve_ebda_region();
+       if (ebda_addr)
+               reserve_bootmem_generic(ebda_addr, ebda_size);
 
 #ifdef CONFIG_SMP
        /*

diff --git a/include/asm-x86_64/e820.h b/include/asm-x86_64/e820.h
index 93b51df5168770547bb0fa8393348af343a7e2a8..670a3388e70a20cc2591e637b698d0649de211f9 100644 (file)
--- a/include/asm-x86_64/e820.h
+++ b/include/asm-x86_64/e820.h
@@ -59,6 +59,8 @@ extern void __init parse_memopt(char *p, char **end);
 extern void __init parse_memmapopt(char *p, char **end);
 
 extern struct e820map e820;
+
+extern unsigned ebda_addr, ebda_size;
 #endif/*!__ASSEMBLY__*/
 
 #endif/*__E820_HEADER*/