Re: [PATCH 04/11] KVM: PPC: fix incorrect element_size for stxsiwx in analyse_instr

[Paul Mackerras <paulus@ozlabs.org>]

On Wed, Apr 25, 2018 at 07:54:37PM +0800, wei.guo.simon@gmail.com wrote:
> From: Simon Guo <wei.guo.simon@gmail.com>
> 
> stwsiwx will place contents of word element 1 of VSR into word
> storage of EA. So the element size of stwsiwx should be 4.
> 
> This patch correct the size from 8 to 4.
> 
> Signed-off-by: Simon Guo <wei.guo.simon@gmail.com>
> ---
>  arch/powerpc/lib/sstep.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
> index 34d68f1..151d484 100644
> --- a/arch/powerpc/lib/sstep.c
> +++ b/arch/powerpc/lib/sstep.c
> @@ -2178,7 +2178,7 @@ int analyse_instr(struct instruction_op *op, const struct pt_regs *regs,
>  		case 140:	/* stxsiwx */
>  			op->reg = rd | ((instr & 1) << 5);
>  			op->type = MKOP(STORE_VSX, 0, 4);
> -			op->element_size = 8;
> +			op->element_size = 4;

I made the element_size be 8 deliberately because this way, with
size=4 but element_size=8, the code will naturally choose the correct
word (the least-significant word of the left half) of the register to
store into memory.  With this change you then need the special case in
a later patch for stxsiwx, which you shouldn't need if you don't make
this change.

Paul.