Re: [PATCH] arm64: tlbflush: avoid writing RES0 bits

[Mark Rutland]

On Wed, Mar 21, 2018 at 05:02:52PM -0400, Philip Elcan wrote:
> Bits [47:44] of the TLBI register operand are RES0 for instructions that
> require a VA, per the ARM ARM spec, so TLBI operations should avoid writing
> non-zero values to these bits.
> 
> Signed-off-by: Philip Elcan <pelcan@xxxxxxxxxxxxxx>
> ---
>  arch/arm64/include/asm/tlbflush.h | 16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h
> index 9e82dd7..dbd22a9 100644
> --- a/arch/arm64/include/asm/tlbflush.h
> +++ b/arch/arm64/include/asm/tlbflush.h
> @@ -60,6 +60,9 @@
>  		__tlbi(op, (arg) | USER_ASID_FLAG);				\
>  } while (0)
>  
> +/* This macro masks out RES0 bits in the TLBI operand */
> +#define __TLBI_VADDR(addr) (addr & ~GENMASK_ULL(47, 44))

If we're going to mask the address bits, it would be simpler to keep the
valid bits than to clear the invalid bits. i.e.

#define __TLBI_VADDR(addr) (addr & GENMASK_ULL(43, 0))

Maybe we want a helper that does all of the addr / asid shifting and
masking, so we do that in one place rather than spreading it across all
helpers, e.g.

#define __tlbi_addr(addr, asid)				\
({							\
	unsigned long __ta = (addr) >> 12;		\
	__ta &= GENMASK_ULL(43, 0);			\
	__ta |= (asid) << 48;				\
	__ta;						\
})

Thanks,
Mark.