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

[Andrew Jones <ajones@ventanamicro.com>]

On Thu, Jul 18, 2024 at 10:09:35AM GMT, Yunhui Cui 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@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;

arm64 show_pte starts with a summary line where the pgtable type (swapper
vs. user), number of VA bits, and physical address of the pgd are
displayed. Should we add that too?

Thanks,
drew

> +	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);
> +	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
> 
> 
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