[PATCH] RISC-V: mm: Fix set_satp_mode() for platform not having Sv57

[Anup Patel]

On Fri, Apr 15, 2022 at 10:18 AM 潘庆霖 <panqinglin2020 at iscas.ac.cn> wrote:
>
> Hi Anup,
>
> >
> > When Sv57 is not available the satp.MODE test in set_satp_mode() will
> > fail and lead to pgdir re-programming for Sv48. The pgdir re-programming
> > will fail as well due to pre-existing pgdir entry used for Sv57 and as
> > a result kernel fails to boot on RISC-V platform not having Sv57.
> >
> > To fix above issue, we should clear the pgdir memory in set_satp_mode()
> > before re-programming.
> >
> > Fixes: 011f09d12052 ("riscv: mm: Set sv57 on defaultly")
> > Reported-by: Mayuresh Chitale <mchitale at ventanamicro.com>
> > Signed-off-by: Anup Patel <apatel at ventanamicro.com>
> > ---
> >  arch/riscv/mm/init.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> > index 9535bea8688c..b0793dc0c291 100644
> > --- a/arch/riscv/mm/init.c
> > +++ b/arch/riscv/mm/init.c
> > @@ -718,6 +718,7 @@ static __init void set_satp_mode(void)
> >            if (!check_l4) {
> >                    disable_pgtable_l5();
> >                    check_l4 = true;
> > +                  memset(early_pg_dir, 0, PAGE_SIZE);
> >                    goto retry;
> >            }
> >            disable_pgtable_l4();
> > --
>
>
> I find it that the set_satp_mode function is in .init.text section which begins at 0x80800000.
> And its pgd_index in both Sv48 and Sv57 will be 0. So it may not be necessary to clear the
> early_pg_dir when the kernel find Sv57 is not supported? And may I get the steps of reproduction
> from you?

We can't assume that it will be the same pgd_index for Sv48 and Sv57.

For example, some hypothetical SoC might have RAM starting after 1TB space.

We should ensure that early_pg_dir is cleaned entirely for detecting the next
mode.

Regards,
Anup

>
> Yours,
> Qinglin
> </apatel at ventanamicro.com></mchitale at ventanamicro.com>