linux-kernel - Re: [PATCH] implement flush_cache_vmap for RISC-V

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Message-ID: <18d198ac-7bc0-934d-e1e9-eca01b790d61@ghiti.fr>
Date:   Wed, 14 Apr 2021 03:03:13 -0400
From:   Alex Ghiti <alex@...ti.fr>
To:     Jisheng Zhang <Jisheng.Zhang@...aptics.com>,
        Jiuyang Liu <liu@...yang.me>
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        Andrew Waterman <waterman@...s.berkeley.edu>,
        Paul Walmsley <paul.walmsley@...ive.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 for RISC-V

Hi,

Le 4/12/21 à 3:08 AM, Jisheng Zhang a écrit :
> Hi Jiuyang,
> 
> On Mon, 12 Apr 2021 00:05:30 +0000 Jiuyang Liu <liu@...yang.me> wrote:
> 
> 
>>
>> This patch implements flush_cache_vmap for RISC-V, since it modifies PTE.
>> Without this patch, SFENCE.VMA won't be added to related codes, which
>> might introduce a bug in the out-of-order micro-architecture
>> implementations.
>>
>> Signed-off-by: Jiuyang Liu <liu@...yang.me>
>> Reviewed-by: Alexandre Ghiti <alex@...ti.fr>
>> Reviewed-by: Palmer Dabbelt <palmer@...belt.com>
> 
> IIRC, Palmer hasn't given this Reviewed-by tag.
> 
>> ---
> 
> Could you plz add version and changes? IIRC, this is the v3.
> 
>>   arch/riscv/include/asm/cacheflush.h | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/arch/riscv/include/asm/cacheflush.h b/arch/riscv/include/asm/cacheflush.h
>> index 23ff70350992..3fd528badc35 100644
>> --- a/arch/riscv/include/asm/cacheflush.h
>> +++ b/arch/riscv/include/asm/cacheflush.h
>> @@ -30,6 +30,12 @@ static inline void flush_dcache_page(struct page *page)
>>   #define flush_icache_user_page(vma, pg, addr, len) \
>>          flush_icache_mm(vma->vm_mm, 0)
>>
>> +/*
>> + * flush_cache_vmap is invoked after map_kernel_range() has installed the page
>> + * table entries, which modifies PTE, SFENCE.VMA should be inserted.
> 
> Just my humble opinion, flush_cache_vmap() may not be necessary. vmalloc_fault
> can take care of this, and finally sfence.vma is inserted in related path.
> 

I believe Palmer and Jisheng are right, my initial proposal to implement 
flush_cache_vmap is wrong.

But then, Jiuyang should not have noticed any problem here, so what's 
wrong? @Jiuyang: Does implementing flush_cache_vmap fix your issue?

And regarding flush_cache_vunmap, from Jisheng call stack, it seems also 
not necessary.

@Jiuyang: Can you tell us more about what you noticed?

> Regards
> 
>> + */
>> +#define flush_cache_vmap(start, end) flush_tlb_all()
>> +
>>   #ifndef CONFIG_SMP
>>
>>   #define flush_icache_all() local_flush_icache_all()
>> --
>> 2.31.1
> 
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> linux-riscv@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv
> 

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