Re: Something very strange on x86_64 2.6.X kernels

[Eric Dumazet <dada1@cosmosbay.com>]

Petr Vandrovec wrote:

> 
> Maybe I already missed answer, but try patch below.  It is definitely bad
> to mark syscall page as global one...
>

Hi Petr

If I follow you, any 64 bits program is corrupted as soon one 32bits 
program using sysenter starts ?

Thank you for the patch, I will try it as soon as possible.
I tried your tpg program and had the same behavior you describe.

I confirm that avoiding the 0xFFFFE000 - 0x100000000 VM ranges is also 
OK , the program never crash...

Eric
> When you build program below, once as 64bit and once as 32bit, 32bit one
> should print 464C457F and 64bit one should die with SIGSEGV.  But when
> you run both in parallel, 64bit one sometime gets SIGSEGV as it should,
> sometime it gets 464C457F. (actually results below are from SMP system;
> I believe that on UP you'll get reproducible 464C457F on UP system...)
> 
> vana:~/64bit-test# ./tpg32
> Memory at ffffe000 is 464C457F
> vana:~/64bit-test# ./tpg
> Segmentation fault
> vana:~/64bit-test# ./tpg32 & ./tpg
> [1] 8450
> Memory at ffffe000 is 464C457F
> Memory at ffffe000 is 464C457F
> [1]+  Exit 31                 ./tpg32
> vana:~/64bit-test# ./tpg32 & ./tpg
> [1] 8454
> Memory at ffffe000 is 464C457F
> [1]+  Exit 31                 ./tpg32
> Segmentation fault
> vana:~/64bit-test# ./tpg32 & ./tpg
> [1] 8456
> Memory at ffffe000 is 464C457F
> Memory at ffffe000 is 464C457F
> [1]+  Exit 31                 ./tpg32
> vana:~/64bit-test# ./tpg32 & ./tpg
> [1] 8458
> Memory at ffffe000 is 464C457F
> Memory at ffffe000 is 464C457F
> [1]+  Exit 31                 ./tpg32
> vana:~/64bit-test#
> 
> 
> void main(void) {
> 	int acc;
> 	int i;
> 
> 	for (i = 0; i < 100000000; i++) ;
> 	acc = *(volatile unsigned long*)(0xffffe000);
> 	printf("Memory at ffffe000 is %08X\n", acc);
> }
> 
> 								Petr
> 
> 
> diff -urdN linux/arch/x86_64/ia32/syscall32.c linux/arch/x86_64/ia32/syscall32.c
> --- linux/arch/x86_64/ia32/syscall32.c	2005-01-17 12:29:05.000000000 +0000
> +++ linux/arch/x86_64/ia32/syscall32.c	2005-01-21 16:15:04.000000000 +0000
> @@ -55,7 +55,7 @@
>   			if (pte_none(*pte)) {
>   				set_pte(pte,
>   					mk_pte(virt_to_page(syscall32_page),
> - 					       PAGE_KERNEL_VSYSCALL));
> + 					       PAGE_KERNEL_VSYSCALL32));
>   			}
>   			/* Flush only the local CPU. Other CPUs taking a fault
>   			   will just end up here again
> diff -urdN linux/include/asm-x86_64/pgtable.h linux/include/asm-x86_64/pgtable.h
> --- linux/include/asm-x86_64/pgtable.h	2005-01-17 12:29:11.000000000 +0000
> +++ linux/include/asm-x86_64/pgtable.h	2005-01-21 16:14:44.000000000 +0000
> @@ -182,6 +182,7 @@
>  #define PAGE_KERNEL_EXEC MAKE_GLOBAL(__PAGE_KERNEL_EXEC)
>  #define PAGE_KERNEL_RO MAKE_GLOBAL(__PAGE_KERNEL_RO)
>  #define PAGE_KERNEL_NOCACHE MAKE_GLOBAL(__PAGE_KERNEL_NOCACHE)
> +#define PAGE_KERNEL_VSYSCALL32 __pgprot(__PAGE_KERNEL_VSYSCALL)
>  #define PAGE_KERNEL_VSYSCALL MAKE_GLOBAL(__PAGE_KERNEL_VSYSCALL)
>  #define PAGE_KERNEL_LARGE MAKE_GLOBAL(__PAGE_KERNEL_LARGE)
>  #define PAGE_KERNEL_VSYSCALL_NOCACHE MAKE_GLOBAL(__PAGE_KERNEL_VSYSCALL_NOCACHE)
> 
>