Commit 8af26be0 authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

perf/core: Fix arch_perf_get_page_size() 



The (new) page-table walker in arch_perf_get_page_size() is broken in
various ways. Specifically while it is used in a lockless manner, it
doesn't depend on CONFIG_HAVE_FAST_GUP nor uses the proper _lockless
offset methods, nor is careful to only read each entry only once.

Also the hugetlb support is broken due to calling pte_page() without
first checking pte_special().

Rewrite the whole thing to be a proper lockless page-table walker and
employ the new pXX_leaf_size() pgtable functions to determine the
pagetable size without looking at the page-frames.

Fixes: 51b646b2 ("perf,mm: Handle non-page-table-aligned hugetlbfs")
Fixes: 8d97e718 ("perf/core: Add PERF_SAMPLE_DATA_PAGE_SIZE")
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: default avatarKan Liang <kan.liang@linux.intel.com>
Link: https://lkml.kernel.org/r/20201126124207.GM3040@hirez.programming.kicks-ass.net
parent 560dabbd

kernel/events/core.c

+38 −65
Original line number Diff line number Diff line
@@ -52,6 +52,7 @@ 
#include <linux/mount.h>

#include <linux/min_heap.h>

#include <linux/highmem.h>

#include <linux/pgtable.h>



#include "internal.h"
@@ -7001,90 +7002,62 @@ static u64 perf_virt_to_phys(u64 virt) 
	return phys_addr;

}



#ifdef CONFIG_MMU



/*

 * Return the MMU page size of a given virtual address.

 *

 * This generic implementation handles page-table aligned huge pages, as well

 * as non-page-table aligned hugetlbfs compound pages.

 *

 * If an architecture supports and uses non-page-table aligned pages in their

 * kernel mapping it will need to provide it's own implementation of this

 * function.

 * Return the pagetable size of a given virtual address.

 */

__weak u64 arch_perf_get_page_size(struct mm_struct *mm, unsigned long addr)

static u64 perf_get_pgtable_size(struct mm_struct *mm, unsigned long addr)

{

	struct page *page;

	pgd_t *pgd;

	p4d_t *p4d;

	pud_t *pud;

	pmd_t *pmd;

	pte_t *pte;

	u64 size = 0;



	pgd = pgd_offset(mm, addr);

	if (pgd_none(*pgd))

		return 0;

#ifdef CONFIG_HAVE_FAST_GUP

	pgd_t *pgdp, pgd;

	p4d_t *p4dp, p4d;

	pud_t *pudp, pud;

	pmd_t *pmdp, pmd;

	pte_t *ptep, pte;



	p4d = p4d_offset(pgd, addr);

	if (!p4d_present(*p4d))

	pgdp = pgd_offset(mm, addr);

	pgd = READ_ONCE(*pgdp);

	if (pgd_none(pgd))

		return 0;



	if (p4d_leaf(*p4d))

		return 1ULL << P4D_SHIFT;

	if (pgd_leaf(pgd))

		return pgd_leaf_size(pgd);



	pud = pud_offset(p4d, addr);

	if (!pud_present(*pud))

	p4dp = p4d_offset_lockless(pgdp, pgd, addr);

	p4d = READ_ONCE(*p4dp);

	if (!p4d_present(p4d))

		return 0;



	if (pud_leaf(*pud)) {

#ifdef pud_page

		page = pud_page(*pud);

		if (PageHuge(page))

			return page_size(compound_head(page));

#endif

		return 1ULL << PUD_SHIFT;

	}

	if (p4d_leaf(p4d))

		return p4d_leaf_size(p4d);



	pmd = pmd_offset(pud, addr);

	if (!pmd_present(*pmd))

	pudp = pud_offset_lockless(p4dp, p4d, addr);

	pud = READ_ONCE(*pudp);

	if (!pud_present(pud))

		return 0;



	if (pmd_leaf(*pmd)) {

#ifdef pmd_page

		page = pmd_page(*pmd);

		if (PageHuge(page))

			return page_size(compound_head(page));

#endif

		return 1ULL << PMD_SHIFT;

	}

	if (pud_leaf(pud))

		return pud_leaf_size(pud);



	pte = pte_offset_map(pmd, addr);

	if (!pte_present(*pte)) {

		pte_unmap(pte);

	pmdp = pmd_offset_lockless(pudp, pud, addr);

	pmd = READ_ONCE(*pmdp);

	if (!pmd_present(pmd))

		return 0;

	}



	page = pte_page(*pte);

	if (PageHuge(page)) {

		u64 size = page_size(compound_head(page));

		pte_unmap(pte);

		return size;

	}

	if (pmd_leaf(pmd))

		return pmd_leaf_size(pmd);



	pte_unmap(pte);

	return PAGE_SIZE;

}



#else

	ptep = pte_offset_map(&pmd, addr);

	pte = ptep_get_lockless(ptep);

	if (pte_present(pte))

		size = pte_leaf_size(pte);

	pte_unmap(ptep);

#endif /* CONFIG_HAVE_FAST_GUP */



static u64 arch_perf_get_page_size(struct mm_struct *mm, unsigned long addr)

{

	return 0;

	return size;

}



#endif



static u64 perf_get_page_size(unsigned long addr)

{

	struct mm_struct *mm;
@@ -7109,7 +7082,7 @@ static u64 perf_get_page_size(unsigned long addr) 
		mm = &init_mm;

	}



	size = arch_perf_get_page_size(mm, addr);

	size = perf_get_pgtable_size(mm, addr);



	local_irq_restore(flags);

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