Re: [PATCH V4 1/2] riscv: Fixup _PAGE_GLOBAL in _PAGE_KERNEL

Guo Ren
2021-05-30T05:34:08Z

On Sun, May 30, 2021 at 7:42 AM <palmerdabbelt@google.com> wrote:
>
> On Tue, 25 May 2021 22:49:20 PDT (-0700), guoren@kernel.org wrote:
> > From: Guo Ren <guoren@linux.alibaba.com>
> >
> > Kernel virtual address translation should avoid to use ASIDs or it'll
> > cause more TLB-miss and TLB-refill. Because the current ASID in satp
> > belongs to the current process, but the target kernel va TLB entry's
> > ASID still belongs to the previous process.
>
> Sorry, I still can't quite figure out what this is trying to say. I
> went ahead and re-wrote the commit text to
>
> riscv: Use global mappings for kernel pages
>
> We map kernel pages into all addresses spages, so they can be marked as
> global. This allows hardware to avoid flushing the kernel mappings when
> moving between address spaces.
Okay

>
> LMK if I'm misunderstanding something here, it's on for-next.
>
> >
> > Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> > Reviewed-by: Anup Patel <anup@brainfault.org>
> > Reviewed-by: Christoph Hellwig <hch@lst.de>
> > Cc: Palmer Dabbelt <palmerdabbelt@google.com>
> > ---
> > arch/riscv/include/asm/pgtable.h | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> > index 9469f46..346a3c6 100644
> > --- a/arch/riscv/include/asm/pgtable.h
> > +++ b/arch/riscv/include/asm/pgtable.h
> > @@ -134,7 +134,8 @@
> > | _PAGE_WRITE \
> > | _PAGE_PRESENT \
> > | _PAGE_ACCESSED \
> > - | _PAGE_DIRTY)
> > + | _PAGE_DIRTY \
> > + | _PAGE_GLOBAL)
> >
> > #define PAGE_KERNEL __pgprot(_PAGE_KERNEL)
> > #define PAGE_KERNEL_READ __pgprot(_PAGE_KERNEL & ~_PAGE_WRITE)

--
Best Regards
Guo Ren

ML: https://lore.kernel.org/linux-csky/