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From:   Guo Ren <guoren@kernel.org>
Date:   Sun, 30 Jul 2023 01:08:17 -0400
Message-ID: <CAJF2gTRm59RAJvSf=L2uqbb3rHnANVheO+yLqrJGuVBh1w8Oug@mail.gmail.com>
Subject: Re: [PATCH -fixes] riscv: Implement flush_cache_vmap()
To:     Alexandre Ghiti <alexghiti@rivosinc.com>
Cc:     Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn@rivosinc.com>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
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On Tue, Jul 25, 2023 at 9:22=E2=80=AFAM Alexandre Ghiti <alexghiti@rivosinc=
.com> wrote:
>
> The RISC-V kernel needs a sfence.vma after a page table modification: we
> used to rely on the vmalloc fault handling to emit an sfence.vma, but
> commit 7d3332be011e ("riscv: mm: Pre-allocate PGD entries for
> vmalloc/modules area") got rid of this path for 64-bit kernels, so now we
> need to explicitly emit a sfence.vma in flush_cache_vmap().
>
> Note that we don't need to implement flush_cache_vunmap() as the generic
> code should emit a flush tlb after unmapping a vmalloc region.
>
> Fixes: 7d3332be011e ("riscv: mm: Pre-allocate PGD entries for vmalloc/mod=
ules area")
> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
> ---
>  arch/riscv/include/asm/cacheflush.h | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/arch/riscv/include/asm/cacheflush.h b/arch/riscv/include/asm=
/cacheflush.h
> index 8091b8bf4883..b93ffddf8a61 100644
> --- a/arch/riscv/include/asm/cacheflush.h
> +++ b/arch/riscv/include/asm/cacheflush.h
> @@ -37,6 +37,10 @@ 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)
>
> +#ifdef CONFIG_64BIT
> +#define flush_cache_vmap(start, end)   flush_tlb_kernel_range(start, end=
)
Sorry, I couldn't agree with the above in a PIPT cache machine. It's
not worth for.

It would reduce the performance of vmap_pages_range,
ioremap_page_range ... API, which may cause some drivers' performance
issues when they install/uninstall memory frequently.

> +#endif
> +
>  #ifndef CONFIG_SMP
>
>  #define flush_icache_all() local_flush_icache_all()
> --
> 2.39.2
>


--=20
Best Regards
 Guo Ren