Re: [RFC V1 04/16] perf/events: Replace READ_ONCE() with standard pgtable accessors

[Anshuman Khandual <anshuman.khandual@arm.com>]

On 24/02/26 3:38 PM, Mark Rutland wrote:
> On Tue, Feb 24, 2026 at 10:41:41AM +0530, Anshuman Khandual wrote:
>> Replace READ_ONCE() with standard page table accessors i.e pxdp_get() which
>> anyways default into READ_ONCE() in cases where platform do not override.
> 
> For each of the patches where you make this sort of change, please
> explain in the commit message *why* it is necessary to do this.

Sure will explain the intent better for these patches.

> > IIUC the entire point of this is that in subsequent patches, arm64 will
> need to use something other than READ_ONCE() for all pXX levels in order
> to support D128 translation tables.

Right.

> 
> Spelling that out in the commit message makes it much easier for
> reviewers to see what's going on, and to focus any discussion/questions,
> e.g. *why* won't READ_ONCE() work?

Got it.

> 
> Mark.
> 
>>
>> Cc: Peter Zijlstra <peterz@infradead.org>
>> Cc: Ingo Molnar <mingo@redhat.com>
>> Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
>> Cc: Namhyung Kim <namhyung@kernel.org>
>> Cc: linux-perf-users@vger.kernel.org
>> Cc: linux-kernel@vger.kernel.org
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
>> ---
>>  kernel/events/core.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>> index ac70d68217b6..4ee151cd2c6d 100644
>> --- a/kernel/events/core.c
>> +++ b/kernel/events/core.c
>> @@ -8422,7 +8422,7 @@ 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;
>>  
>> @@ -8430,7 +8430,7 @@ 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;
>>  
>> @@ -8438,7 +8438,7 @@ 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;
>>  
>> -- 
>> 2.43.0
>>