[PATCH 1/2] powerpc/xmon: support dumping software pagetables

[Ram Pai]

On Fri, Jul 21, 2017 at 03:24:05PM +1000, Balbir Singh wrote:
> It would be nice to be able to dump page tables in a
> particular context
> 
> Example use cases
> 
> Dumping PTE contents to see the keys (useful for debugging)
> 
> c0000000ba48c880 c0000000bab438b0   2677   2675 T  2 protection_keys
> 0:mon> ds c0000000ba48c880 0x7ffff7f70000
> translating tsk c0000000ba48c880, addr 7ffff7f70000
> G: 0xb95b6400   U: 0xb6334000   M: 0xb6543000   PA: 0x012c0000, PTE: 0xd4800000012c0504
> 
> Dumping vmalloc space
> 
> 0:mon> ds 0 d000000000000000
> translating tsk           (null), addr d000000000000000
> G: 0x3d450400   U: 0xbc184000   M: 0x3d460000   PA: 0x7e010000, PTE: 0xc08000007e01018e
> 
> I did not replicate the complex code of dump_pagetable and have no support
> for bolted linear mapping, thats why I've called it software pagetable
> dumping support. The format of the PTE can be expanded to add more useful
> information about the flags in the PTE if required.

yes. a nice way of dumping all the flags in the PTE will be handy.
especially; my favorite, protection key values.

> 
> Signed-off-by: Balbir Singh <bsingharora at gmail.com>
> ---
>  arch/powerpc/xmon/xmon.c | 97 ++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 97 insertions(+)
> 
> diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
> index 08e367e..8aedfff 100644
> --- a/arch/powerpc/xmon/xmon.c
> +++ b/arch/powerpc/xmon/xmon.c
> @@ -126,6 +126,7 @@ static void byterev(unsigned char *, int);
>  static void memex(void);
>  static int bsesc(void);
>  static void dump(void);
> +static void show_pte(unsigned long);
>  static void prdump(unsigned long, long);
>  static int ppc_inst_dump(unsigned long, long, int);
>  static void dump_log_buf(void);
> @@ -233,6 +234,7 @@ Commands:\n\
>  #endif
>    "\
>    dr	dump stream of raw bytes\n\
> +  ds	dump software PTEs\n\
>    dt	dump the tracing buffers (uses printk)\n\
>  "
>  #ifdef CONFIG_PPC_POWERNV
> @@ -2528,6 +2530,9 @@ dump(void)
>  	} else if (c == 't') {
>  		ftrace_dump(DUMP_ALL);
>  		tracing_on();
> +	} else if (c == 's') {
> +		/* dump software pte */
> +		show_pte(adrs);
>  	} else if (c == 'r') {
>  		scanhex(&ndump);
>  		if (ndump == 0)
> @@ -2860,7 +2865,99 @@ static void show_task(struct task_struct *tsk)
>  		state, task_thread_info(tsk)->cpu,
>  		tsk->comm);
>  }
> +void format_pte(unsigned long pte)
> +{
> +	unsigned long pa = pte & PTE_RPN_MASK;
> +
> +	printf("PA: 0x%08lx, PTE: 0x%08lx\n", pa, pte);
> +}
> +
> +static void show_pte(unsigned long tskv)
> +{
> +	unsigned long addr = 0;
> +	struct task_struct *tsk = NULL;
> +	struct mm_struct *mm;
> +	pgd_t *pgdp;
> +	pud_t *pudp;
> +	pmd_t *pmdp;
> +	pte_t *ptep;
> +
> +	tsk = (struct task_struct *)tskv;
> +	if (tsk == NULL)
> +		mm = &init_mm;
> +	else
> +		mm = tsk->active_mm;
> +
> +	if (mm == NULL)
> +		mm = &init_mm;
> +
> +	if (!scanhex(&addr))
> +		printf("need address to translate\n");
> +
> +	if (setjmp(bus_error_jmp) != 0) {
> +		catch_memory_errors = 0;
> +		printf("*** Error dumping pte for task %p\n", tsk);
> +		return;
> +	}
> +
> +	catch_memory_errors = 1;
> +	sync();
> +
> +	if (mm == &init_mm)
> +		pgdp = pgd_offset_k(addr);
> +	else
> +		pgdp = pgd_offset(mm, addr);
> +
> +	if (pgd_none(*pgdp)) {
> +		printf("no linux page table for address\n");
> +		return;
> +	}
> 
> +	if (pgd_huge(*pgdp)) {
> +		format_pte(pgd_val(*pgdp));
> +		return;
> +	}
> +	printf("G: 0x%8lx\t", pgd_val(*pgdp));
> +
> +	pudp = pud_offset(pgdp, addr);
> +
> +	if (pud_none(*pudp)) {
> +		printf("No valid PUD\n");
> +		return;
> +	}
> +
> +	if (pud_huge(*pudp)) {
> +		format_pte(pud_val(*pudp));
> +		return;
> +	}
> +	printf("U: 0x%8lx\t", pud_val(*pudp));
> +
> +	pmdp = pmd_offset(pudp, addr);
> +
> +	if (pmd_none(*pmdp)) {
> +		printf("No valid PMD\n");
> +		return;
> +	}
> +
> +	if (pmd_huge(*pmdp)) {
> +		format_pte(pmd_val(*pmdp));
> +		return;
> +	}
> +	printf("M: 0x%8lx\t", pmd_val(*pmdp));
> +
> +	/* pte_offset_map is the same as pte_offset_kernel */
> +	ptep = pte_offset_kernel(pmdp, addr);
> +	if (pte_none(*ptep)) {
> +		printf("no valid PTE\n");
> +		return;
> +	}
> +
> +	format_pte(pte_val(*ptep));
> +

These two lines below always go togather. A nice macro
#define sync_delay() { sync(); __delay(200); }
can help.

> +	sync();
> +	__delay(200);


> +	catch_memory_errors = 0;


> +}
>  static void show_tasks(void)
>  {
>  	unsigned long tskv;
> -- 
> 2.9.4

-- 
Ram Pai