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Calculate TASK_SIZE at run-time by figuring out the host's VMSPLIT - this is needed on i386 if UML is to run on hosts with varying VMSPLITs without recompilation. TASK_SIZE is now defined in terms of a variable, task_size. This gets rid of an include of pgtable.h from processor.h, which can cause include loops. On i386, task_size is calculated early in boot by probing the address space in a binary search to figure out where the boundary between usable and non-usable memory is. This tries to make sure that a page that is considered to be in userspace is, or can be made, read-write. I'm concerned about a system-global VDSO page in kernel memory being hit and considered to be a userspace page. On x86_64, task_size is just the old value of CONFIG_TOP_ADDR. A bunch of config variable are gone now. CONFIG_TOP_ADDR is directly replaced by TASK_SIZE. NEST_LEVEL is gone since the relocation of the stubs makes it irrelevant. All the HOST_VMSPLIT stuff is gone. All references to these in arch/um/Makefile are also gone. I noticed and fixed a missing extern in os.h when adding os_get_task_size. Note: This has been revised to fix the 32-bit UML on 64-bit host bug that Miklos ran into. Signed-off-by: Jeff Dike <[email protected]> Cc: Miklos Szeredi <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,120 @@ | ||
| #include <stdio.h> | ||
| #include <stdlib.h> | ||
| #include <signal.h> | ||
| #include <sys/mman.h> | ||
| #include "longjmp.h" | ||
| #include "kern_constants.h" | ||
|
|
||
| static jmp_buf buf; | ||
|
|
||
| static void segfault(int sig) | ||
| { | ||
| longjmp(buf, 1); | ||
| } | ||
|
|
||
| static int page_ok(unsigned long page) | ||
| { | ||
| unsigned long *address = (unsigned long *) (page << UM_KERN_PAGE_SHIFT); | ||
| unsigned long n = ~0UL; | ||
| void *mapped = NULL; | ||
| int ok = 0; | ||
|
|
||
| /* | ||
| * First see if the page is readable. If it is, it may still | ||
| * be a VDSO, so we go on to see if it's writable. If not | ||
| * then try mapping memory there. If that fails, then we're | ||
| * still in the kernel area. As a sanity check, we'll fail if | ||
| * the mmap succeeds, but gives us an address different from | ||
| * what we wanted. | ||
| */ | ||
| if (setjmp(buf) == 0) | ||
| n = *address; | ||
| else { | ||
| mapped = mmap(address, UM_KERN_PAGE_SIZE, | ||
| PROT_READ | PROT_WRITE, | ||
| MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); | ||
| if (mapped == MAP_FAILED) | ||
| return 0; | ||
| if (mapped != address) | ||
| goto out; | ||
| } | ||
|
|
||
| /* | ||
| * Now, is it writeable? If so, then we're in user address | ||
| * space. If not, then try mprotecting it and try the write | ||
| * again. | ||
| */ | ||
| if (setjmp(buf) == 0) { | ||
| *address = n; | ||
| ok = 1; | ||
| goto out; | ||
| } else if (mprotect(address, UM_KERN_PAGE_SIZE, | ||
| PROT_READ | PROT_WRITE) != 0) | ||
| goto out; | ||
|
|
||
| if (setjmp(buf) == 0) { | ||
| *address = n; | ||
| ok = 1; | ||
| } | ||
|
|
||
| out: | ||
| if (mapped != NULL) | ||
| munmap(mapped, UM_KERN_PAGE_SIZE); | ||
| return ok; | ||
| } | ||
|
|
||
| unsigned long os_get_task_size(void) | ||
| { | ||
| struct sigaction sa, old; | ||
| unsigned long bottom = 0; | ||
| /* | ||
| * A 32-bit UML on a 64-bit host gets confused about the VDSO at | ||
| * 0xffffe000. It is mapped, is readable, can be reprotected writeable | ||
| * and written. However, exec discovers later that it can't be | ||
| * unmapped. So, just set the highest address to be checked to just | ||
| * below it. This might waste some address space on 4G/4G 32-bit | ||
| * hosts, but shouldn't hurt otherwise. | ||
| */ | ||
| unsigned long top = 0xffffd000 >> UM_KERN_PAGE_SHIFT; | ||
| unsigned long test; | ||
|
|
||
| printf("Locating the top of the address space ... "); | ||
| fflush(stdout); | ||
|
|
||
| /* | ||
| * We're going to be longjmping out of the signal handler, so | ||
| * SA_DEFER needs to be set. | ||
| */ | ||
| sa.sa_handler = segfault; | ||
| sigemptyset(&sa.sa_mask); | ||
| sa.sa_flags = SA_NODEFER; | ||
| sigaction(SIGSEGV, &sa, &old); | ||
|
|
||
| if (!page_ok(bottom)) { | ||
| fprintf(stderr, "Address 0x%x no good?\n", | ||
| bottom << UM_KERN_PAGE_SHIFT); | ||
| exit(1); | ||
| } | ||
|
|
||
| /* This could happen with a 4G/4G split */ | ||
| if (page_ok(top)) | ||
| goto out; | ||
|
|
||
| do { | ||
| test = bottom + (top - bottom) / 2; | ||
| if (page_ok(test)) | ||
| bottom = test; | ||
| else | ||
| top = test; | ||
| } while (top - bottom > 1); | ||
|
|
||
| out: | ||
| /* Restore the old SIGSEGV handling */ | ||
| sigaction(SIGSEGV, &old, NULL); | ||
|
|
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| top <<= UM_KERN_PAGE_SHIFT; | ||
| printf("0x%x\n", top); | ||
| fflush(stdout); | ||
|
|
||
| return top; | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,5 @@ | ||
| unsigned long os_get_task_size(unsigned long shift) | ||
| { | ||
| /* The old value of CONFIG_TOP_ADDR */ | ||
| return 0x7fc0000000; | ||
| } |
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