Re: [PATCH 02/10] arm64: KVM: Add invalidate_icache_range helper

[Will Deacon <will.deacon@arm.com>]

On Mon, Oct 09, 2017 at 04:20:24PM +0100, Marc Zyngier wrote:
> We currently tightly couple dcache clean with icache invalidation,
> but KVM could do without the initial flush to PoU, as we've
> already flushed things to PoC.
> 
> Let's introduce invalidate_icache_range which is limited to
> invalidating the icache from the linear mapping (and thus
> has none of the userspace fault handling complexity), and
> wire it in KVM instead of flush_icache_range.
> 
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
>  arch/arm64/include/asm/cacheflush.h |  8 ++++++++
>  arch/arm64/include/asm/kvm_mmu.h    |  4 ++--
>  arch/arm64/mm/cache.S               | 24 ++++++++++++++++++++++++
>  3 files changed, 34 insertions(+), 2 deletions(-)

[...]

> diff --git a/arch/arm64/mm/cache.S b/arch/arm64/mm/cache.S
> index 7f1dbe962cf5..0c330666a8c9 100644
> --- a/arch/arm64/mm/cache.S
> +++ b/arch/arm64/mm/cache.S
> @@ -80,6 +80,30 @@ USER(9f, ic	ivau, x4	)		// invalidate I line PoU
>  ENDPROC(flush_icache_range)
>  ENDPROC(__flush_cache_user_range)
>  
> +/*
> + *	invalidate_icache_range(start,end)
> + *
> + *	Ensure that the I cache is invalid within specified region. This
> + *	assumes that this is done on the linear mapping. Do not use it
> + *	on a userspace range, as this may fault horribly.
> + *
> + *	- start   - virtual start address of region
> + *	- end     - virtual end address of region
> + */
> +ENTRY(invalidate_icache_range)
> +	icache_line_size x2, x3
> +	sub	x3, x2, #1
> +	bic	x4, x0, x3
> +1:
> +	ic	ivau, x4			// invalidate I line PoU
> +	add	x4, x4, x2
> +	cmp	x4, x1
> +	b.lo	1b
> +	dsb	ish
> +	isb
> +	ret
> +ENDPROC(invalidate_icache_range)

Is there a good reason not to make this work for user addresses? If it's as
simple as adding a USER annotation and a fallback, then we should wrap that
in a macro and reuse it for __flush_cache_user_range.

Will