Re: [PATCH] implement flush_cache_vmap for RISC-V

[Alex Ghiti]

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@xxxxxxxxxx> 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@xxxxxxxxxx>
> > Reviewed-by: Alexandre Ghiti <alex@xxxxxxxx>
> > Reviewed-by: Palmer Dabbelt <palmer@xxxxxxxxxxx>
>
> 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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