[Crash-utility] [PATCH] s390x: Fix virtual address check for 5 level page tables

[Dave Anderson]

----- Original Message -----
> Hello Dave,
> 
> We have recently found that Crash is not capable of processing 5 level
> page tables virtual addresses (higher than 8 Petabytes). Please find the
> enclosed patch below.
> 
> Thanks,
> Mikhail Zaslonko

Hi Mikhail,

For the changelog, can you give an example of the symptoms of the
failure?  Does it fail to handle kernel modules during session 
initialization, or what?

Thanks,
  Dave


> 
> 
> [PATCH] s390x: Fix virtual address check for 5 level page tables
> 
> 
> The current validity check for virtual addresses fails for
> five level page tables because in that case it uses a 64 bit
> left-shift operation which is undefined in the C standard.
> 
> Quote from C99 standard:
> 
>   If the  value  of  the  right  operand  is  negative or is
>   greater than or equal to the width of the promoted left operand,
>   the behavior is undefined.
> 
> To fix this, we just skip the validity check in case of highest
> page-level (level = 3) due to redundancy
> 
> Signed-off-by: Mikhail Zaslonko <zaslonko at linux.vnet.ibm.com>
> ---
>   s390x.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/s390x.c b/s390x.c
> index e13bd59..96ce3dc 100644
> --- a/s390x.c
> +++ b/s390x.c
> @@ -688,7 +688,7 @@ int s390x_vtop(ulong table, ulong vaddr, physaddr_t
> *phys_addr, int verbose)
>   	/* Read the first entry to find the number of page table levels. */
>   	readmem(table, KVADDR, &entry, sizeof(entry), "entry", FAULT_ON_ERROR);
>   	level = (entry & 0xcULL) >> 2;
> -	if ((vaddr >> (31 + 11*level)) != 0ULL) {
> +	if ((level < 3) && (vaddr >> (31 + 11*level)) != 0ULL) {
>   		/* Address too big for the number of page table levels. */
>   		return FALSE;
>   	}
> --
> 2.10.2
> 
>