[PATCH v2] riscv/mm/fault: add show_pte() before die()

[Andrew Jones]

On Mon, Jul 22, 2024 at 12:20:37PM 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 at bytedance.com>
> Reviewed-by: Alexandre Ghiti <alexghiti at rivosinc.com>
> ---
>  arch/riscv/mm/fault.c | 53 +++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 53 insertions(+)
> 
> diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
> index 5224f3733802..666d282a8bf4 100644
> --- a/arch/riscv/mm/fault.c
> +++ b/arch/riscv/mm/fault.c
> @@ -22,6 +22,58 @@
>  
>  #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;
> +
> +	pr_alert("Current %s pgtable: %luK pagesize, %d-bit VAs, pgdp=0x%016lx\n",
> +		 current->comm, PAGE_SIZE/SZ_1K, VA_BITS,
> +		 (mm == &init_mm ? __pa_symbol(mm->pgd) :
> +		 (unsigned long)virt_to_phys(mm->pgd)));

nit: unnecessary () around the ternary.

> +
> +	pgdp = pgd_offset(mm, addr);
> +	pgd = pgdp_get(pgdp);
> +	pr_alert("[%016lx] pgd=%016lx", addr, pgd_val(pgd));
> +	if (pgd_none(pgd) || pgd_bad(pgd) || pgd_leaf(pgd))
> +		goto out;
> +
> +	p4dp = p4d_offset(pgdp, addr);
> +	p4d = p4dp_get(p4dp);
> +	pr_cont(", p4d=%016lx", p4d_val(p4d));
> +	if (p4d_none(p4d) || p4d_bad(p4d) || p4d_leaf(p4d))
> +		goto out;
> +
> +	pudp = pud_offset(p4dp, addr);
> +	pud = pudp_get(pudp);
> +	pr_cont(", pud=%016lx", pud_val(pud));
> +	if (pud_none(pud) || pud_bad(pud) || pud_leaf(pud))
> +		goto out;
> +
> +	pmdp = pmd_offset(pudp, addr);
> +	pmd = pmdp_get(pmdp);
> +	pr_cont(", pmd=%016lx", pmd_val(pmd));
> +	if (pmd_none(pmd) || pmd_bad(pmd) || pmd_leaf(pmd))
> +		goto out;
> +
> +	ptep = pte_offset_map(pmdp, addr);
> +	if (!ptep)
> +		goto out;
> +
> +	pte = ptep_get(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 +83,7 @@ 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
> 
>

Reviewed-by: Andrew Jones <ajones at ventanamicro.com>

Thanks,
drew