Re: [PATCH] implement flush_cache_vmap and flush_cache_vunmap for RISC-V

From: Alex Ghiti <alex@ghiti.fr>
To: Jiuyang Liu <liu@jiuyang.me>
Cc: Andrew Waterman <waterman@eecs.berkeley.edu>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Andrew Morton <akpm@linux-foundation.org>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] implement flush_cache_vmap and flush_cache_vunmap for RISC-V
Date: Tue, 30 Mar 2021 03:02:50 -0400	[thread overview]
Message-ID: <9749165b-32d4-94a2-7c8a-e219fdf1b102@ghiti.fr> (raw)
In-Reply-To: <20210329015510.44110-1-liu@jiuyang.me>

Hi Jiuyang,

Le 3/28/21 à 9:55 PM, Jiuyang Liu a écrit :
> This patch implements flush_cache_vmap and flush_cache_vunmap for
> RISC-V, since these functions might modify PTE. Without this patch,
> SFENCE.VMA won't be added to related codes, which might introduce a bug
> in some out-of-order micro-architecture implementations.
> 
> Signed-off-by: Jiuyang Liu <liu@jiuyang.me>
> ---
>   arch/riscv/include/asm/cacheflush.h | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/cacheflush.h b/arch/riscv/include/asm/cacheflush.h
> index 23ff70350992..4adf25248c43 100644
> --- a/arch/riscv/include/asm/cacheflush.h
> +++ b/arch/riscv/include/asm/cacheflush.h
> @@ -8,6 +8,14 @@
>   
>   #include <linux/mm.h>
>   
> +/*
> + * flush_cache_vmap and flush_cache_vunmap might modify PTE, needs SFENCE.VMA.

"might modify PTE" is not entirely true I think, this is what happens 
before using this function that might modify PTE, those functions ensure 
those modifications are made visible.

> + * - flush_cache_vmap is invoked after map_kernel_range() has installed the page table entries.
> + * - flush_cache_vunmap is invoked before unmap_kernel_range() deletes the page table entries
> + */
> +#define flush_cache_vmap(start, end) flush_tlb_all()
> +#define flush_cache_vunmap(start, end) flush_tlb_all()
> +
>   static inline void local_flush_icache_all(void)
>   {
>   	asm volatile ("fence.i" ::: "memory");
> 

FWIW, you can add:

Reviewed-by: Alexandre Ghiti <alex@ghiti.fr>

Thanks,

Alex

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