Re: [PATCH V4 01/13] perf/core, x86: Add PERF_SAMPLE_DATA_PAGE_SIZE

Peter Zijlstra
2019-02-01T09:22:49Z

On Thu, Jan 31, 2019 at 12:27:54PM -0800, kan.liang@linux.intel.com wrote:
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index 374a197..229a73b 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -2578,3 +2578,34 @@ void perf_get_x86_pmu_capability(struct x86_pmu_capability *cap)
> cap->events_mask_len = x86_pmu.events_mask_len;
> }
> EXPORT_SYMBOL_GPL(perf_get_x86_pmu_capability);
> +
> +u64 perf_get_page_size(u64 virt)
> +{
> + unsigned long flags;
> + unsigned int level;
> + pte_t *pte;
> +
> + if (!virt)
> + return 0;
> +
> + /*
> + * Interrupts are disabled, so it prevents any tear down
> + * of the page tables.
> + * See the comment near struct mmu_table_batch.
> + */
> + local_irq_save(flags);
> + if (virt >= TASK_SIZE)
> + pte = lookup_address(virt, &level);
> + else {
> + if (current->mm) {
> + pte = lookup_address_in_pgd(pgd_offset(current->mm, virt),
> + virt, &level);
> + } else
> + level = PG_LEVEL_NUM;
> + }
> + local_irq_restore(flags);
> + if (level >= PG_LEVEL_NUM)
> + return 0;
> +
> + return (u64)page_level_size(level);
> +}

*sigh* there really isn't anything x86 specific there.

> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 236bb8d..d233f45 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -6352,6 +6358,12 @@ static u64 perf_virt_to_phys(u64 virt)
> return phys_addr;
> }
>
> +/* Return page size of given virtual address. IRQ-safe required. */
> +u64 __weak perf_get_page_size(u64 virt)
> +{
> + return 0;
> +}
> +
> static struct perf_callchain_entry __empty_callchain = { .nr = 0, };
>
> struct perf_callchain_entry *

How about something like so instead?

(completely untested, will likely make your grandma eat puppies)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6357,10 +6357,72 @@ static u64 perf_virt_to_phys(u64 virt)
return phys_addr;
}

-/* Return page size of given virtual address. IRQ-safe required. */
-u64 __weak perf_get_page_size(u64 virt)
+static u64 __perf_get_page_size(struct mm_struct *mm, unsigned long addr)
{
- return 0;
+ pgd_t *pgd;
+ p4d_t *p4d;
+ pud_t *pud;
+ pmd_t *pmd;
+
+ pgd = pgd_offset(mm, addr);
+ if (pgd_none(*pgd))
+ return 0;
+
+ p4d = p4d_offset(pgd, addr);
+ if (p4d_none(*p4d))
+ return 0;
+
+ if (p4d_large(*p4d));
+ return 1ULL << P4D_SHIFT;
+
+ if (!p4d_present(*p4d))
+ return 0;
+
+ pud = pud_offset(p4d, addr);
+ if (pud_none(*pud))
+ return 0;
+
+ if (pud_large(*pud))
+ return 1ULL << PUD_SHIFT;
+
+ if (!pud_present(*pud))
+ return 0;
+
+ pmd = pmd_offset(pud, addr);
+ if (pmd_none(*pmd))
+ return 0;
+
+ if (pmd_large(*pmd))
+ return 1ULL << PMD_SHIFT;
+
+ if (!pmd_present(*pmd))
+ return 0;
+
+ return 1ULL << PAGE_SHIFT;
+}
+
+static u64 perf_get_page_size(unsigned long addr)
+{
+ struct mm_struct *mm;
+ unsigned long flags;
+ u64 ret;
+
+ /*
+ * Software page-table walkers must disable IRQs, see asm-generic/tlb.h.
+ */
+ local_irq_save(flags);
+ mm = current->mm;
+ if (!mm) {
+ /*
+ * For kernel threads and the like, use init_mm so that
+ * we can find kernel memory.
+ */
+ mm = &init_mm;
+ }
+ ret = __perf_get_page_size(mm, addr);
+ local_irq_restore(flags);
+
+ return ret;
}

static struct perf_callchain_entry __empty_callchain = { .nr = 0, };