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Fix lguest page-pinning logic ("lguest: bad stack page 0xc057a000")

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If the stack pointer is 0xc057a000, then the first stack page is at
0xc0579000 (the stack pointer is decremented before use).  Not
calculating this correctly caused guests with CONFIG_DEBUG_PAGEALLOC=y
to be killed with a "bad stack page" message: the initial kernel stack
was just proceeding the .smp_locks section which
CONFIG_DEBUG_PAGEALLOC marks read-only when freeing.

Thanks to Frederik Deweerdt for the bug report!

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Rusty Russell 2007-08-30 06:35:08 +10:00 committed by Linus Torvalds
parent b07d68b5ca
commit 8057d763ed
1 changed files with 5 additions and 2 deletions
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7
drivers/lguest/interrupts_and_traps.c
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@ -270,8 +270,11 @@ void pin_stack_pages(struct lguest *lg)
/* Depending on the CONFIG_4KSTACKS option, the Guest can have one or
* two pages of stack space. */
for (i = 0; i < lg->stack_pages; i++)
/* The stack grows *upwards*, hence the subtraction */
pin_page(lg, lg->esp1 - i * PAGE_SIZE);
/* The stack grows *upwards*, so the address we're given is the
* start of the page after the kernel stack. Subtract one to
* get back onto the first stack page, and keep subtracting to
* get to the rest of the stack pages. */
pin_page(lg, lg->esp1 - 1 - i * PAGE_SIZE);
}
/* Direct traps also mean that we need to know whenever the Guest wants to use