Re: [PATCH] powerpc: handle VSX alignment faults correctly in little-endian mode

[Michael Neuling <mikey@neuling.org>]

> This patch fixes the handling of VSX alignment faults in little-endian
> mode (the current code assumes the processor is in big-endian mode).
> 
> The patch also makes the handlers clear the top 8 bytes of the register
> when handling an 8 byte VSX load.
> 
> This is based on 2.6.32.
> 
> Signed-off-by: Neil Campbell <neilc@linux.vnet.ibm.com>

Thanks for this Neil!

Acked-by: Michael Neuling <mikey@neuling.org>

> Cc: <stable@kernel.org>
> ---
> diff --git a/arch/powerpc/kernel/align.c b/arch/powerpc/kernel/align.c
> index a5b632e..f0c624f 100644
> --- a/arch/powerpc/kernel/align.c
> +++ b/arch/powerpc/kernel/align.c
> @@ -642,10 +642,14 @@ static int emulate_spe(struct pt_regs *regs, unsigned i
nt reg,
>   */
>  static int emulate_vsx(unsigned char __user *addr, unsigned int reg,
>  		       unsigned int areg, struct pt_regs *regs,
> -		       unsigned int flags, unsigned int length)
> +		       unsigned int flags, unsigned int length,
> +		       unsigned int elsize)
>  {
>  	char *ptr;
> +	unsigned long *lptr;
>  	int ret = 0;
> +	int sw = 0;
> +	int i, j;
>  
>  	flush_vsx_to_thread(current);
>  
> @@ -654,19 +658,35 @@ static int emulate_vsx(unsigned char __user *addr, unsi
gned int reg,
>  	else
>  		ptr = (char *) &current->thread.vr[reg - 32];
>  
> -	if (flags & ST)
> -		ret = __copy_to_user(addr, ptr, length);
> -        else {
> -		if (flags & SPLT){
> -			ret = __copy_from_user(ptr, addr, length);
> -			ptr += length;
> +	lptr = (unsigned long *) ptr;
> +
> +	if (flags & SW)
> +		sw = elsize-1;
> +
> +	for (j = 0; j < length; j += elsize) {
> +		for (i = 0; i < elsize; ++i) {
> +			if (flags & ST)
> +				ret |= __put_user(ptr[i^sw], addr + i);
> +			else
> +				ret |= __get_user(ptr[i^sw], addr + i);
>  		}
> -		ret |= __copy_from_user(ptr, addr, length);
> +		ptr  += elsize;
> +		addr += elsize;
>  	}
> -	if (flags & U)
> -		regs->gpr[areg] = regs->dar;
> -	if (ret)
> +
> +	if (!ret) {
> +		if (flags & U)
> +			regs->gpr[areg] = regs->dar;
> +
> +		/* Splat load copies the same data to top and bottom 8 bytes */
> +		if (flags & SPLT)
> +			lptr[1] = lptr[0];
> +		/* For 8 byte loads, zero the top 8 bytes */
> +		else if (!(flags & ST) && (8 == length))
> +			lptr[1] = 0;
> +	} else
>  		return -EFAULT;
> +
>  	return 1;
>  }
>  #endif
> @@ -767,16 +787,25 @@ int fix_alignment(struct pt_regs *regs)
>  
>  #ifdef CONFIG_VSX
>  	if ((instruction & 0xfc00003e) == 0x7c000018) {
> -		/* Additional register addressing bit (64 VSX vs 32 FPR/GPR */
> +		unsigned int elsize;
> +
> +		/* Additional register addressing bit (64 VSX vs 32 FPR/GPR) */
>  		reg |= (instruction & 0x1) << 5;
>  		/* Simple inline decoder instead of a table */
> +		/* VSX has only 8 and 16 byte memory accesses */
> +		nb = 8;
>  		if (instruction & 0x200)
>  			nb = 16;
> -		else if (instruction & 0x080)
> -			nb = 8;
> -		else
> -			nb = 4;
> +
> +		/* Vector stores in little-endian mode swap individual
> +		   elements, so process them separately */
> +		elsize = 4;
> +		if (instruction & 0x80)
> +			elsize = 8;
> +
>  		flags = 0;
> +		if (regs->msr & MSR_LE)
> +			flags |= SW;
>  		if (instruction & 0x100)
>  			flags |= ST;
>  		if (instruction & 0x040)
> @@ -787,7 +816,7 @@ int fix_alignment(struct pt_regs *regs)
>  			nb = 8;
>  		}
>  		PPC_WARN_EMULATED(vsx);
> -		return emulate_vsx(addr, reg, areg, regs, flags, nb);
> +		return emulate_vsx(addr, reg, areg, regs, flags, nb, elsize);
>  	}
>  #endif
>  	/* A size of 0 indicates an instruction we don't support, with
>