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Introduce a write acessor for updating the current LDT. This is required
for hypervisors like Xen that do not allow LDT pages to be directly
written.
Testing - here's a fun little LDT test that can be trivially modified to
test limits as well.
/*
* Copyright (c) 2005, Zachary Amsden (zach@vmware.com)
* This is licensed under the GPL.
*/
#include <stdio.h>
#include <signal.h>
#include <asm/ldt.h>
#include <asm/segment.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/mman.h>
#define __KERNEL__
#include <asm/page.h>
void main(void)
{
struct user_desc desc;
char *code;
unsigned long long tsc;
code = (char *)mmap(0, 8192, PROT_EXEC|PROT_READ|PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
desc.entry_number = 0;
desc.base_addr = code;
desc.limit = 1;
desc.seg_32bit = 1;
desc.contents = MODIFY_LDT_CONTENTS_CODE;
desc.read_exec_only = 0;
desc.limit_in_pages = 1;
desc.seg_not_present = 0;
desc.useable = 1;
if (modify_ldt(1, &desc, sizeof(desc)) != 0) {
perror("modify_ldt");
}
printf("code base is 0x%08x\n", (unsigned)code);
code[0x0ffe] = 0x0f; /* rdtsc */
code[0x0fff] = 0x31;
code[0x1000] = 0xcb; /* lret */
__asm__ __volatile("lcall $7,$0xffe" : "=A" (tsc));
printf("TSC is 0x%016llx\n", tsc);
}
Signed-off-by: Zachary Amsden <zach@vmware.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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