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

Palmer Dabbelt
2020-08-05T02:03:10Z

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barriers used for page table modifications") is out of date, as I can't find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?

>>
>> static pte_t *__init get_pte_virt(phys_addr_t pa)
>> --
>> 2.28.0
>>
>
> Otherwise looks good to me.
>
> Reviewed-by: Anup Patel <anup@brainfault.org>
>
> Regards,
> Anup