linux-kernel - Re: [PATCH v5 5/6] arm64: move ARM64_HAS_CACHE_DIC/

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Date:   Tue, 14 Jan 2020 18:26:41 +0000
From:   Will Deacon <will@...nel.org>
To:     Pavel Tatashin <pasha.tatashin@...een.com>
Cc:     jmorris@...ei.org, sashal@...nel.org, linux-kernel@...r.kernel.org,
        catalin.marinas@....com, steve.capper@....com,
        linux-arm-kernel@...ts.infradead.org, maz@...nel.org,
        james.morse@....com, vladimir.murzin@....com, mark.rutland@....com,
        tglx@...utronix.de, gregkh@...uxfoundation.org,
        allison@...utok.net, info@...ux.net, alexios.zavras@...el.com,
        sstabellini@...nel.org, boris.ostrovsky@...cle.com,
        jgross@...e.com, stefan@...er.ch, yamada.masahiro@...ionext.com,
        xen-devel@...ts.xenproject.org, linux@...linux.org.uk,
        andrew.cooper3@...rix.com, julien@....org
Subject: Re: [PATCH v5 5/6] arm64: move ARM64_HAS_CACHE_DIC/_IDC from asm to C

On Thu, Jan 02, 2020 at 04:13:56PM -0500, Pavel Tatashin wrote:
> The assmbly functions __asm_flush_cache_user_range and
> __asm_invalidate_icache_range have alternatives:
> 
> alternative_if ARM64_HAS_CACHE_DIC
> ...
> 
> alternative_if ARM64_HAS_CACHE_IDC
> ...
> 
> But, the implementation of those alternatives is trivial and therefore
> can be done in the C inline wrappers.
> 
> Signed-off-by: Pavel Tatashin <pasha.tatashin@...een.com>
> ---
>  arch/arm64/include/asm/cacheflush.h | 19 +++++++++++++++++++
>  arch/arm64/mm/cache.S               | 27 +++++----------------------
>  arch/arm64/mm/flush.c               |  1 +
>  3 files changed, 25 insertions(+), 22 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/cacheflush.h b/arch/arm64/include/asm/cacheflush.h
> index 047af338ba15..fc5217a18398 100644
> --- a/arch/arm64/include/asm/cacheflush.h
> +++ b/arch/arm64/include/asm/cacheflush.h
> @@ -77,8 +77,22 @@ static inline long __flush_cache_user_range(unsigned long start,
>  {
>  	int ret;
>  
> +	if (cpus_have_const_cap(ARM64_HAS_CACHE_IDC)) {
> +		dsb(ishst);
> +		if (cpus_have_const_cap(ARM64_HAS_CACHE_DIC)) {
> +			isb();
> +			return 0;
> +		}
> +	}
> +
>  	uaccess_ttbr0_enable();
>  	ret = __asm_flush_cache_user_range(start, end);

I don't understand this. Doesn't it mean a CPU with IDC but not DIC will
end up with doing the D-cache maintenance?

Will