linux-kernel - Re: [PATCH V4 01/13] perf/core, x86: Add PERF_SAMPLE_DATA_PAGE

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Date:   Fri, 1 Feb 2019 10:22:40 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     kan.liang@...ux.intel.com
Cc:     acme@...nel.org, tglx@...utronix.de, mingo@...hat.com,
        linux-kernel@...r.kernel.org, eranian@...gle.com, jolsa@...hat.com,
        namhyung@...nel.org, ak@...ux.intel.com, luto@...capital.net,
        Vlastimil Babka <vbabka@...e.cz>, kirill@...temov.name
Subject: Re: [PATCH V4 01/13] perf/core, x86: Add PERF_SAMPLE_DATA_PAGE_SIZE

On Thu, Jan 31, 2019 at 12:27:54PM -0800, kan.liang@...ux.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, };