[External] Re: [PATCH] riscv/mm/fault: add show_pte() before die()

[yunhui cui]

Hi Alex，

On Sat, Jul 20, 2024 at 12:26 AM Alexandre Ghiti <alexghiti at rivosinc.com> wrote:
>
> Hi Yunhui,
>
> On Thu, Jul 18, 2024 at 4:20 AM Yunhui Cui <cuiyunhui at bytedance.com> wrote:
> >
> > When the kernel displays "Unable to handle kernel paging request at
> > virtual address", we would like to confirm the status of the virtual
> > address in the page table. So add show_pte() before die().
> >
> > Signed-off-by: Yunhui Cui <cuiyunhui at bytedance.com>
> > ---
> >  arch/riscv/mm/fault.c | 47 +++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 47 insertions(+)
> >
> > diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
> > index 90d4ba36d1d0..dfe3ce38e16b 100644
> > --- a/arch/riscv/mm/fault.c
> > +++ b/arch/riscv/mm/fault.c
> > @@ -22,6 +22,52 @@
> >
> >  #include "../kernel/head.h"
> >
> > +static void show_pte(unsigned long addr)
> > +{
> > +       pgd_t *pgdp, pgd;
> > +       p4d_t *p4dp, p4d;
> > +       pud_t *pudp, pud;
> > +       pmd_t *pmdp, pmd;
> > +       pte_t *ptep, pte;
> > +       struct mm_struct *mm = current->mm;
> > +
> > +       if (!mm)
> > +               mm = &init_mm;
> > +       pgdp = pgd_offset(mm, addr);
> > +       pgd = READ_ONCE(*pgdp);
> > +       pr_alert("[%016lx] pgd=%016lx", addr, pgd_val(pgd));
> > +       if (pgd_none(pgd) || pgd_bad(pgd))
> > +               goto out;
> > +
> > +       p4dp = p4d_offset(pgdp, addr);
> > +       p4d = READ_ONCE(*p4dp);
> > +       pr_cont(", p4d=%016lx", p4d_val(p4d));
> > +       if (p4d_none(p4d) || p4d_bad(p4d))
> > +               goto out;
> > +
> > +       pudp = pud_offset(p4dp, addr);
> > +       pud = READ_ONCE(*pudp);
> > +       pr_cont(", pud=%016lx", pud_val(pud));
> > +       if (pud_none(pud) || pud_bad(pud))
> > +               goto out;
> > +
> > +       pmdp = pmd_offset(pudp, addr);
> > +       pmd = READ_ONCE(*pmdp);
> > +       pr_cont(", pmd=%016lx", pmd_val(pmd));
> > +       if (pmd_none(pmd) || pmd_bad(pmd))
> > +               goto out;
> > +
> > +       ptep = pte_offset_map(pmdp, addr);
> > +       if (!ptep)
> > +               goto out;
> > +
> > +       pte = READ_ONCE(*ptep);
>
> All the READ_ONCE() can be replaced by pXXp_get() macros defined here:
> https://elixir.bootlin.com/linux/v6.10/source/include/linux/pgtable.h#L315
>
> And we should stop as soon as we encounter a leaf entry using pXd_leaf().
>
Okay, I'll update it in v2.

> Thanks,
>
> Alex
>
> > +       pr_cont(", pte=%016lx", pte_val(pte));
> > +       pte_unmap(ptep);
> > +out:
> > +       pr_cont("\n");
> > +}
> > +
> >  static void die_kernel_fault(const char *msg, unsigned long addr,
> >                 struct pt_regs *regs)
> >  {
> > @@ -31,6 +77,7 @@ static void die_kernel_fault(const char *msg, unsigned long addr,
> >                 addr);
> >
> >         bust_spinlocks(0);
> > +       show_pte(addr);
> >         die(regs, "Oops");
> >         make_task_dead(SIGKILL);
> >  }
> > --
> > 2.39.2
> >
>
> Otherwise, that's a good idea to print the page table content on fault so:
>
> Reviewed-by: Alexandre Ghiti <alexghiti at rivosinc.com>
>
> Thanks,
>
> Alex

Thanks,
Yunhui