On Thu, Nov 26, 2020 at 01:01:17PM +0100, Peter Zijlstra wrote:
> 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: 51b646b2d9f8 ("perf,mm: Handle non-page-table-aligned hugetlbfs")
> Fixes: 8d97e71811aa ("perf/core: Add PERF_SAMPLE_DATA_PAGE_SIZE")
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Tested-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> ---
> arch/arm64/include/asm/pgtable.h | 3 +
> arch/sparc/include/asm/pgtable_64.h | 13 ++++
> arch/sparc/mm/hugetlbpage.c | 19 ++++--
> include/linux/pgtable.h | 16 +++++
> kernel/events/core.c | 102 +++++++++++++-----------------------
> 5 files changed, 82 insertions(+), 71 deletions(-)
This diffstat doesn't match the patch in this email ...
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -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 +7001,62 @@ 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;
> - }
> -
> - pte_unmap(pte);
> - return PAGE_SIZE;
> -}
> + if (pmd_leaf(pmd))
> + return pmd_leaf_size(pmd);
>
> -#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 +7081,7 @@ static u64 perf_get_page_size(unsigned l
> mm = &init_mm;
> }
>
> - size = arch_perf_get_page_size(mm, addr);
> + size = perf_get_pgtable_size(mm, addr);
>
> local_irq_restore(flags);
>
>
>
