Re: [Qemu-devel] [PATCH] target-s390x: fix LOAD MULTIPLE instruction on page boundary

[Richard Henderson <rth@twiddle.net>]

On 05/21/2015 02:32 PM, Aurelien Jarno wrote:
> When consecutive memory locations are on page boundary a page fault
> might occur when using the LOAD MULTIPLE instruction. In that case real
> hardware doesn't load any register.
> 
> This is an important detail in case the base register is in the list
> of registers to be loaded. If a page fault occurs this register might be
> overwritten and when the instruction is later restarted the wrong
> base register value is useD.
> 
> Fix this by first loading all values from memory and then writing them
> back to the registers.
> 
> This fixes random segmentation faults seen in the guest.
> 
> Cc: Alexander Graf <agraf@suse.de>
> Cc: Richard Henderson <rth@twiddle.net>
> Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
> ---
>  target-s390x/translate.c | 56 +++++++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 51 insertions(+), 5 deletions(-)

Hmm.  Seems to be un/under-specified in the PoO.  That said,

Reviewed-by: Richard Henderson <rth@twiddle.net>

It would be nice to know if there ought to be similar up-front access checking
for STM, to avoid errant partial stores.


r~