linux-kernel - Re: [PATCH] implement flush_cache_vmap and flush_cache

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Date:   Tue, 30 Mar 2021 03:02:50 -0400
From:   Alex Ghiti <alex@...ti.fr>
To:     Jiuyang Liu <liu@...yang.me>
Cc:     Andrew Waterman <waterman@...s.berkeley.edu>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] implement flush_cache_vmap and flush_cache_vunmap for
 RISC-V

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@...yang.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@...ti.fr>

Thanks,

Alex