Re: [PATCH] riscv: Add sfence.vma after page table changed

Greentime Hu
2020-09-15T03:58:34Z

Palmer Dabbelt <palmer@dabbelt.com> 於 2020年8月5日 週三 上午10:03寫道：
>
> On Mon, 03 Aug 2020 20:29:32 PDT (-0700), anup@brainfault.org wrote:
> > On Tue, Aug 4, 2020 at 8:32 AM Greentime Hu <greentime.hu@sifive.com> wrote:
> >>
> >> This patch addes local_flush_tlb_page(addr) to use sfence.vma after the
> >
> > s/addes/adds
> >
> >> page table changed. That address will be used immediately in
> >> memset(nextp, 0, PAGE_SIZE) to cause this issue so we should add the
> >> sfence.vma before we use it.
> >
> > Alternate version of this commit description can be:
> >
> > Invalidate local TLB after both set_pet() and clear_pte() because the
> > address can be used immediately after page table change.
> >
> >> Fixes: f2c17aabc917 ("RISC-V: Implement compile-time fixed mappings")
> >>
> >> Reported-by: Syven Wang <syven.wang@sifive.com>
> >> Signed-off-by: Syven Wang <syven.wang@sifive.com>
> >> Signed-off-by: Greentime Hu <greentime.hu@sifive.com>
> >> ---
> >> arch/riscv/mm/init.c | 7 +++----
> >> 1 file changed, 3 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> >> index f4adb3684f3d..29b0f7108054 100644
> >> --- a/arch/riscv/mm/init.c
> >> +++ b/arch/riscv/mm/init.c
> >> @@ -202,12 +202,11 @@ void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot)
> >>
> >> ptep = &fixmap_pte[pte_index(addr)];
> >>
> >> - if (pgprot_val(prot)) {
> >> + if (pgprot_val(prot))
> >> set_pte(ptep, pfn_pte(phys >> PAGE_SHIFT, prot));
> >> - } else {
> >> + else
> >> pte_clear(&init_mm, addr, ptep);
> >> - local_flush_tlb_page(addr);
> >> - }
> >> + local_flush_tlb_page(addr);
> >> }
>
> arm64 appears to be upgrading all set_pte()s on valid kernel mappings to
> include the fence. It looks like the message from 7f0b1bf04511 ("arm64: Fix
> barriers used for page table modifications") is out of date, as I can't find
> create_mapping() any more. If that was some generic kernel thing then we
> should probably upgrade ours as well, but if it was arch/arm64/ code then this
> approach seems fine as __set_fixmap() isn't on the hot path -- I guess this is
> fine either way, but there may be other issues that the arm64 approach fixes.
>
> Do you guys happen to remember what was going on here?

Hi Palmer,

Some architectures add cache writeback in set_pte(), just like nds32, csky.

https://github.com/torvalds/linux/blob/master/arch/nds32/include/asm/pgtable.h#L213
https://github.com/torvalds/linux/blob/master/arch/csky/include/asm/pgtable.h#L104

Would you like to pick this patch or should I send another patch to
implement it in set_pte()?