linux-kernel - Re: [PATCH v5 05/17] arm64: pgtable: use mmu gather to free p4d level page table

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Message-ID: <a017d072-943f-4008-bb1d-7be438804a44@bytedance.com>
Date: Tue, 14 Jan 2025 10:26:54 +0800
From: Qi Zheng <zhengqi.arch@...edance.com>
To: Will Deacon <will@...nel.org>
Cc: peterz@...radead.org, agordeev@...ux.ibm.com, kevin.brodsky@....com,
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Subject: Re: [PATCH v5 05/17] arm64: pgtable: use mmu gather to free p4d level
 page table

Hi Will,

On 2025/1/14 00:26, Will Deacon wrote:
> On Wed, Jan 08, 2025 at 02:57:21PM +0800, Qi Zheng wrote:
>> Like other levels of page tables, also use mmu gather mechanism to free
>> p4d level page table.
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
>> Originally-by: Peter Zijlstra (Intel) <peterz@...radead.org>
>> Reviewed-by: Kevin Brodsky <kevin.brodsky@....com>
>> Cc: linux-arm-kernel@...ts.infradead.org
>> ---
>>   arch/arm64/include/asm/pgalloc.h |  1 -
>>   arch/arm64/include/asm/tlb.h     | 14 ++++++++++++++
>>   2 files changed, 14 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/include/asm/pgalloc.h b/arch/arm64/include/asm/pgalloc.h
>> index 2965f5a7e39e3..1b4509d3382c6 100644
>> --- a/arch/arm64/include/asm/pgalloc.h
>> +++ b/arch/arm64/include/asm/pgalloc.h
>> @@ -85,7 +85,6 @@ static inline void pgd_populate(struct mm_struct *mm, pgd_t *pgdp, p4d_t *p4dp)
>>   	__pgd_populate(pgdp, __pa(p4dp), pgdval);
>>   }
>>   
>> -#define __p4d_free_tlb(tlb, p4d, addr)  p4d_free((tlb)->mm, p4d)
>>   #else
>>   static inline void __pgd_populate(pgd_t *pgdp, phys_addr_t p4dp, pgdval_t prot)
>>   {
>> diff --git a/arch/arm64/include/asm/tlb.h b/arch/arm64/include/asm/tlb.h
>> index a947c6e784ed2..445282cde9afb 100644
>> --- a/arch/arm64/include/asm/tlb.h
>> +++ b/arch/arm64/include/asm/tlb.h
>> @@ -111,4 +111,18 @@ static inline void __pud_free_tlb(struct mmu_gather *tlb, pud_t *pudp,
>>   }
>>   #endif
>>   
>> +#if CONFIG_PGTABLE_LEVELS > 4
>> +static inline void __p4d_free_tlb(struct mmu_gather *tlb, p4d_t *p4dp,
>> +				  unsigned long addr)
>> +{
>> +	struct ptdesc *ptdesc = virt_to_ptdesc(p4dp);
>> +
>> +	if (!pgtable_l5_enabled())
>> +		return;
>> +
>> +	pagetable_p4d_dtor(ptdesc);
>> +	tlb_remove_ptdesc(tlb, ptdesc);
>> +}
> 
> Should we update p4d_free() to call the destructor, too? It looks like
> it just does free_page() atm.

The patch #3 introduces the generic p4d_free() and lets arm64 to use it.
The patch #4 adds the destructor to generic p4d_free(). So IIUC, there
is no problem here.

Thanks!

> 
> Will