Commit 5a84b600 authored by Anshuman Khandual's avatar Anshuman Khandual Committed by Peter Zijlstra
Browse files

perf/events: Replace READ_ONCE() with standard pgtable accessors 



Replace raw READ_ONCE() dereferences of pgtable entries with corresponding
standard page table accessors pxdp_get() in perf_get_pgtable_size(). These
accessors default to READ_ONCE() on platforms that don't override them. So
there is no functional change on such platforms.

However arm64 platform is being extended to support 128 bit page tables via
a new architecture feature i.e FEAT_D128 in which case READ_ONCE() will not
provide required single copy atomic access for 128 bit page table entries.
Although pxdp_get() accessors can later be overridden on arm64 platform to
extend required single copy atomicity support on 128 bit entries.

Signed-off-by: default avatarAnshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260227062744.2215491-1-anshuman.khandual@arm.com
parent 9805ed3c

kernel/events/core.c

+3 −3
Original line number Diff line number Diff line
@@ -8421,7 +8421,7 @@ static u64 perf_get_pgtable_size(struct mm_struct *mm, unsigned long addr) 
	pte_t *ptep, pte;



	pgdp = pgd_offset(mm, addr);

	pgd = READ_ONCE(*pgdp);

	pgd = pgdp_get(pgdp);

	if (pgd_none(pgd))

		return 0;
@@ -8429,7 +8429,7 @@ static u64 perf_get_pgtable_size(struct mm_struct *mm, unsigned long addr) 
		return pgd_leaf_size(pgd);



	p4dp = p4d_offset_lockless(pgdp, pgd, addr);

	p4d = READ_ONCE(*p4dp);

	p4d = p4dp_get(p4dp);

	if (!p4d_present(p4d))

		return 0;
@@ -8437,7 +8437,7 @@ static u64 perf_get_pgtable_size(struct mm_struct *mm, unsigned long addr) 
		return p4d_leaf_size(p4d);



	pudp = pud_offset_lockless(p4dp, p4d, addr);

	pud = READ_ONCE(*pudp);

	pud = pudp_get(pudp);

	if (!pud_present(pud))

		return 0;