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

Will Deacon
2017-10-19T16:46:28Z

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