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From: Mark Rutland <mark.rutland@arm.com>
To: Fuad Tabba <tabba@google.com>
Cc: "moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)"
	<linux-arm-kernel@lists.infradead.org>,
	Will Deacon <will@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Marc Zyngier <maz@kernel.org>, Ard Biesheuvel <ardb@kernel.org>,
	James Morse <james.morse@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>
Subject: Re: [PATCH v1 01/13] arm64: Do not enable uaccess for flush_icache_range
Date: Wed, 12 May 2021 11:53:08 +0100	[thread overview]
Message-ID: <20210512105308.GE88854@C02TD0UTHF1T.local> (raw)
In-Reply-To: <CA+EHjTxQYzKWyQzy1PUpynzTFUcDOcS=zDi9xq5QWFf4MAqNDA@mail.gmail.com>

On Wed, May 12, 2021 at 11:29:53AM +0100, Fuad Tabba wrote:
> Hi Mark,
> 
> On Wed, May 12, 2021 at 10:59 AM Mark Rutland <mark.rutland@arm.com> wrote:
> >
> > On Wed, May 12, 2021 at 09:52:28AM +0100, Fuad Tabba wrote:
> > > Hi Mark,
> > >
> > > > > No functional change intended.
> > > >
> > > > There is a performance change here, since the existing
> > > > `__flush_cache_user_range` takes IDC and DIC into account, whereas
> > > > `invalidate_icache_by_line` does not.
> > >
> > > You're right. There is a performance change in this patch and a couple
> > > of the others, which I will note in v2. However, I don't think that
> > > this patch changes the behavior when it comes to IDC and DIC, does it?
> >
> > It shouldn't be a functional problem, but it means that the new
> > `__flush_icache_range` will always perform redundant I-cache maintenance
> > rather than skipping this when the cpu has DIC=1.
> 
> Sorry, but I can't quite see how this patch is making a difference in
> that regard. The existing code has __flush_icache_range fallthrough to
> __flush_cache_user_range, where the alternative_if
> ARM64_HAS_CACHE_{IDC,DIC} are invoked.
> 
> In this patch, __flush_icache_range and __flush_cache_user_range share
> the same code via the macro, where the alternative_ifs and branches
> over invalidate_icache_by_line are still there and behave the same:
> the macro jumps to 8 if ARM64_HAS_CACHE_DIC, avoiding any redundant
> cache maintenance.
> 
> Am I missing something else?

No; you're absolutely right. I had misread the patch and thought the
IDC/DIC parts didn't go into the common macro. That all looks fine.

Sorry again for the noise.

Thanks,
Mark.

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  reply	other threads:[~2021-05-12 10:55 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-11 14:42 [PATCH v1 00/13] Tidy up cache.S Fuad Tabba
2021-05-11 14:42 ` [PATCH v1 01/13] arm64: Do not enable uaccess for flush_icache_range Fuad Tabba
2021-05-11 15:22   ` Mark Rutland
2021-05-12  8:52     ` Fuad Tabba
2021-05-12  9:59       ` Mark Rutland
2021-05-12 10:29         ` Fuad Tabba
2021-05-12 10:53           ` Mark Rutland [this message]
2021-05-11 16:53   ` Robin Murphy
2021-05-12  8:57     ` Fuad Tabba
2021-05-11 14:42 ` [PATCH v1 02/13] arm64: Do not enable uaccess for invalidate_icache_range Fuad Tabba
2021-05-11 15:34   ` Mark Rutland
2021-05-12  9:35     ` Fuad Tabba
2021-05-11 14:42 ` [PATCH v1 03/13] arm64: Downgrade flush_icache_range to invalidate Fuad Tabba
2021-05-11 14:53   ` Ard Biesheuvel
2021-05-12  9:45     ` Fuad Tabba
2021-05-11 14:42 ` [PATCH v1 04/13] arm64: Move documentation of dcache_by_line_op Fuad Tabba
2021-05-11 14:42 ` [PATCH v1 05/13] arm64: __inval_dcache_area to take end parameter instead of size Fuad Tabba
2021-05-11 14:42 ` [PATCH v1 06/13] arm64: dcache_by_line_op " Fuad Tabba
2021-05-11 14:42 ` [PATCH v1 07/13] arm64: __flush_dcache_area " Fuad Tabba
2021-05-11 14:42 ` [PATCH v1 08/13] arm64: __clean_dcache_area_poc " Fuad Tabba
2021-05-11 14:42 ` [PATCH v1 09/13] arm64: __clean_dcache_area_pop " Fuad Tabba
2021-05-11 14:42 ` [PATCH v1 10/13] arm64: __clean_dcache_area_pou " Fuad Tabba
2021-05-11 14:42 ` [PATCH v1 11/13] arm64: sync_icache_aliases " Fuad Tabba
2021-05-11 14:42 ` [PATCH v1 12/13] arm64: Fix cache maintenance function comments Fuad Tabba
2021-05-11 14:42 ` [PATCH v1 13/13] arm64: Rename arm64-internal cache maintenance functions Fuad Tabba
2021-05-11 15:09   ` Ard Biesheuvel
2021-05-11 15:49     ` Mark Rutland
2021-05-12  9:51       ` Marc Zyngier
2021-05-12 10:00         ` Mark Rutland
2021-05-12 10:00       ` Fuad Tabba
2021-05-12 10:04         ` Mark Rutland
2021-05-12  9:56     ` Fuad Tabba

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