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From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: Sami Tolvanen <samitolvanen@google.com>,
	Kees Cook <keescook@chromium.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Ard Biesheuvel <ardb@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	linux-arm-kernel@lists.infradead.org, llvm@lists.linux.dev
Subject: Re: [PATCH v5 04/10] ARM: mm: Type-annotate all cache assembly routines
Date: Mon, 29 Apr 2024 14:18:28 +0100	[thread overview]
Message-ID: <Zi+eJM8+ulDBYGrQ@shell.armlinux.org.uk> (raw)
In-Reply-To: <20240415-arm32-cfi-v5-4-ff11093eeccc@linaro.org>

On Mon, Apr 15, 2024 at 03:43:23PM +0200, Linus Walleij wrote:
> -ENTRY(fa_flush_user_cache_all)
> -	/* FALLTHROUGH */
> +SYM_TYPED_FUNC_START(fa_flush_user_cache_all)
> +	b	fa_flush_kern_cache_all
> +SYM_FUNC_END(fa_flush_user_cache_all)

The thing I don't like about this is that it makes these functions
less efficient - the early CPUs do _not_ have branch predictors,
and they flush the pipeline on branches, so rather than just dropping
rough, this kind of thing introduces pointless multi-cycle delays for
functionality just to keep CFI happy.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!

WARNING: multiple messages have this Message-ID (diff)
From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: Sami Tolvanen <samitolvanen@google.com>,
	Kees Cook <keescook@chromium.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Ard Biesheuvel <ardb@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	linux-arm-kernel@lists.infradead.org, llvm@lists.linux.dev
Subject: Re: [PATCH v5 04/10] ARM: mm: Type-annotate all cache assembly routines
Date: Mon, 29 Apr 2024 14:18:28 +0100	[thread overview]
Message-ID: <Zi+eJM8+ulDBYGrQ@shell.armlinux.org.uk> (raw)
In-Reply-To: <20240415-arm32-cfi-v5-4-ff11093eeccc@linaro.org>

On Mon, Apr 15, 2024 at 03:43:23PM +0200, Linus Walleij wrote:
> -ENTRY(fa_flush_user_cache_all)
> -	/* FALLTHROUGH */
> +SYM_TYPED_FUNC_START(fa_flush_user_cache_all)
> +	b	fa_flush_kern_cache_all
> +SYM_FUNC_END(fa_flush_user_cache_all)

The thing I don't like about this is that it makes these functions
less efficient - the early CPUs do _not_ have branch predictors,
and they flush the pipeline on branches, so rather than just dropping
rough, this kind of thing introduces pointless multi-cycle delays for
functionality just to keep CFI happy.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  parent reply	other threads:[~2024-04-29 13:18 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-04-15 13:43 [PATCH v5 00/10] CFI for ARM32 using LLVM Linus Walleij
2024-04-15 13:43 ` Linus Walleij
2024-04-15 13:43 ` [PATCH v5 01/10] ARM: bugs: Check in the vtable instead of defined aliases Linus Walleij
2024-04-15 13:43   ` Linus Walleij
2024-04-15 13:43 ` [PATCH v5 02/10] ARM: ftrace: Define ftrace_stub_graph Linus Walleij
2024-04-15 13:43   ` Linus Walleij
2024-04-15 13:43 ` [PATCH v5 03/10] ARM: mm: Make tlbflush routines CFI safe Linus Walleij
2024-04-15 13:43   ` Linus Walleij
2024-04-15 13:43 ` [PATCH v5 04/10] ARM: mm: Type-annotate all cache assembly routines Linus Walleij
2024-04-15 16:35   ` Ard Biesheuvel
2024-04-15 16:35     ` Ard Biesheuvel
2024-04-16  7:38     ` Linus Walleij
2024-04-16  7:38       ` Linus Walleij
2024-04-29 13:18   ` Russell King (Oracle) [this message]
2024-04-29 13:18     ` Russell King (Oracle)
2024-04-15 13:43 ` [PATCH v5 05/10] ARM: mm: Rewrite cacheflush vtables in CFI safe C Linus Walleij
2024-04-15 13:43   ` Linus Walleij
2024-04-15 13:43 ` [PATCH v5 06/10] ARM: mm Type-annotate all per-processor assembly routines Linus Walleij
2024-04-15 13:43   ` Linus Walleij
2024-04-15 13:43 ` [PATCH v5 07/10] ARM: mm: Define prototypes for all per-processor calls Linus Walleij
2024-04-15 13:43   ` Linus Walleij
2024-04-15 13:43 ` [PATCH v5 08/10] ARM: lib: Annotate loop delay instructions for CFI Linus Walleij
2024-04-15 13:43   ` Linus Walleij
2024-04-15 13:43 ` [PATCH v5 09/10] ARM: hw_breakpoint: Handle CFI breakpoints Linus Walleij
2024-04-15 13:43   ` Linus Walleij
2024-04-15 13:43 ` [PATCH v5 10/10] ARM: Support CLANG CFI Linus Walleij
2024-04-15 13:43   ` Linus Walleij

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