linux-kernel - Re: [patches] [PATCH 3/4] RISC-V: Flush I$ when making a dirty page executable

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Date:   Thu, 30 Nov 2017 12:32:04 -0800
From:   Olof Johansson <olof@...om.net>
To:     patches@...ups.riscv.org
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Waterman <andrew@...ive.com>,
        Palmer Dabbelt <palmer@...ive.com>
Subject: Re: [patches] [PATCH 3/4] RISC-V: Flush I$ when making a dirty page executable

Hi,

On Mon, Nov 20, 2017 at 10:57 AM, Palmer Dabbelt <palmer@...ive.com> wrote:
> From: Andrew Waterman <andrew@...ive.com>
>
> The RISC-V ISA allows for instruction caches that are not coherent WRT
> stores, even on a single hart.  As a result, we need to explicitly flush
> the instruction cache whenever marking a dirty page as executable in
> order to preserve the correct system behavior.
>
> Local instruction caches aren't that scary (our implementations actually
> flush the cache, but RISC-V is defined to allow higher-performance
> implementations to exist), but RISC-V defines no way to perform an
> instruction cache shootdown.  When explicitly asked to do so we can
> shoot down remote instruction caches via an IPI, but this is a bit on
> the slow side.
>
> Instead of requiring an IPI to all harts whenever marking a page as
> executable, we simply flush the currently running harts.  In order to
> maintain correct behavior, we additionally mark every other hart as
> needing a deferred instruction cache which will be taken before anything
> runs on it.
>
> Signed-off-by: Andrew Waterman <andrew@...ive.com>
> Signed-off-by: Palmer Dabbelt <palmer@...ive.com>
> ---
>  arch/riscv/include/asm/cacheflush.h  | 24 ++++++++++++---
>  arch/riscv/include/asm/mmu.h         |  4 +++
>  arch/riscv/include/asm/mmu_context.h | 44 +++++++++++++++++++++++++++
>  arch/riscv/include/asm/pgtable.h     | 58 ++++++++++++++++++++----------------
>  arch/riscv/include/asm/tlbflush.h    |  2 ++
>  arch/riscv/kernel/smp.c              | 48 +++++++++++++++++++++++++++++
>  arch/riscv/mm/Makefile               |  2 ++
>  arch/riscv/mm/cacheflush.c           | 23 ++++++++++++++
>  8 files changed, 175 insertions(+), 30 deletions(-)
>  create mode 100644 arch/riscv/mm/cacheflush.c

[...]

> diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
> index 81f7d9ce6d88..786b5fdec0fd 100644
> --- a/arch/riscv/mm/Makefile
> +++ b/arch/riscv/mm/Makefile
> @@ -2,3 +2,5 @@ obj-y += init.o
>  obj-y += fault.o
>  obj-y += extable.o
>  obj-y += ioremap.o
> +obj-y += dma.o
> +obj-y += cacheflush.o

Looks like dma.c didn't make it into this patch (and didn't already
exist), so builds fail with:

 make[3]: *** No rule to make target 'arch/riscv/mm/dma.o', needed by
'arch/riscv/mm/built-in.o'.


-Olof