unimore/kernel-hacking-2024-linux-steffo
unimore/kernel-hacking-2024-linux-steffo
1
Fork 0
Code Pull requests 5 Wiki Activity

perf/core: Fix arch_perf_get_page_size()

Browse source 
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: 51b646b2d9 ("perf,mm: Handle non-page-table-aligned hugetlbfs")
Fixes: 8d97e71811 ("perf/core: Add PERF_SAMPLE_DATA_PAGE_SIZE")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Kan Liang <kan.liang@linux.intel.com>
Link: https://lkml.kernel.org/r/20201126124207.GM3040@hirez.programming.kicks-ass.net
This commit is contained in:
Peter Zijlstra 2020-11-11 13:43:57 +01:00
parent 560dabbdf6
commit 8af26be062
1 changed files with 40 additions and 67 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

107
kernel/events/core.c
View file

@ -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))
#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;
pgdp = pgd_offset(mm, addr);
pgd = READ_ONCE(*pgdp);
if (pgd_none(pgd))
return 0;
p4d = p4d_offset(pgd, addr);
if (!p4d_present(*p4d))
if (pgd_leaf(pgd))
return pgd_leaf_size(pgd);
p4dp = p4d_offset_lockless(pgdp, pgd, addr);
p4d = READ_ONCE(*p4dp);
if (!p4d_present(p4d))
return 0;
if (p4d_leaf(*p4d))
return 1ULL << P4D_SHIFT;
if (p4d_leaf(p4d))
return p4d_leaf_size(p4d);
pud = pud_offset(p4d, addr);
if (!pud_present(*pud))
pudp = pud_offset_lockless(p4dp, p4d, addr);
pud = READ_ONCE(*pudp);
if (!pud_present(pud))
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 (pud_leaf(pud))
return pud_leaf_size(pud);
pmd = pmd_offset(pud, addr);
if (!pmd_present(*pmd))
pmdp = pmd_offset_lockless(pudp, pud, addr);
pmd = READ_ONCE(*pmdp);
if (!pmd_present(pmd))
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 (pmd_leaf(pmd))
return pmd_leaf_size(pmd);
pte = pte_offset_map(pmd, addr);
if (!pte_present(*pte)) {
pte_unmap(pte);
return 0;
}
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 */
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;
return size;
}
#else
static u64 arch_perf_get_page_size(struct mm_struct *mm, unsigned long addr)
{
return 0;
}
#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);