linux-kernel - Re: [PATCH -fixes 2/2] riscv: Fix set_huge_pte_at() for NAPOT mappings when a swap entry is set

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Date:   Mon, 2 Oct 2023 09:18:52 +0200
From:   Alexandre Ghiti <alex@...ti.fr>
To:     Conor Dooley <conor@...nel.org>,
        Alexandre Ghiti <alexghiti@...osinc.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Andrew Jones <ajones@...tanamicro.com>,
        Qinglin Pan <panqinglin2020@...as.ac.cn>,
        Ryan Roberts <ryan.roberts@....com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -fixes 2/2] riscv: Fix set_huge_pte_at() for NAPOT
 mappings when a swap entry is set

Hi Conor,

On 30/09/2023 11:14, Conor Dooley wrote:
> On Thu, Sep 28, 2023 at 05:18:46PM +0200, Alexandre Ghiti wrote:
>> We used to determine the number of page table entries to set for a NAPOT
>> hugepage by using the pte value which actually fails when the pte to set is
>> a swap entry.
>>
>> So take advantage of a recent fix for arm64 reported in [1] which
>> introduces the size of the mapping as an argument of set_huge_pte_at(): we
>> can then use this size to compute the number of page table entries to set
>> for a NAPOT region.
>>
>> Fixes: 82a1a1f3bfb6 ("riscv: mm: support Svnapot in hugetlb page")
>> Reported-by: Ryan Roberts <ryan.roberts@....com>
>> Closes: https://lore.kernel.org/linux-arm-kernel/20230922115804.2043771-1-ryan.roberts@arm.com/ [1]
>> Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
> Breaks the build. Your $subject marks this for -fixes, but this will not
> build there, as it relies on content that's not yet in that branch.
> AFAICT, you're going to have to resend this with akpm on CC, as the
> dependency is in his tree...

I see, but I still don't understand why -fixes does not point to the 
latest rcX instead of staying on rc1? The patch which this series 
depends on just made it to rc4.

Thanks,

Alex

> Thanks,
> Conor.
>
>> ---
>>   arch/riscv/mm/hugetlbpage.c | 19 +++++++++++++------
>>   1 file changed, 13 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/riscv/mm/hugetlbpage.c b/arch/riscv/mm/hugetlbpage.c
>> index e4a2ace92dbe..b52f0210481f 100644
>> --- a/arch/riscv/mm/hugetlbpage.c
>> +++ b/arch/riscv/mm/hugetlbpage.c
>> @@ -183,15 +183,22 @@ void set_huge_pte_at(struct mm_struct *mm,
>>   		     pte_t pte,
>>   		     unsigned long sz)
>>   {
>> +	unsigned long hugepage_shift;
>>   	int i, pte_num;
>>   
>> -	if (!pte_napot(pte)) {
>> -		set_pte_at(mm, addr, ptep, pte);
>> -		return;
>> -	}
>> +	if (sz >= PGDIR_SIZE)
>> +		hugepage_shift = PGDIR_SHIFT;
>> +	else if (sz >= P4D_SIZE)
>> +		hugepage_shift = P4D_SHIFT;
>> +	else if (sz >= PUD_SIZE)
>> +		hugepage_shift = PUD_SHIFT;
>> +	else if (sz >= PMD_SIZE)
>> +		hugepage_shift = PMD_SHIFT;
>> +	else
>> +		hugepage_shift = PAGE_SHIFT;
>>   
>> -	pte_num = napot_pte_num(napot_cont_order(pte));
>> -	for (i = 0; i < pte_num; i++, ptep++, addr += PAGE_SIZE)
>> +	pte_num = sz >> hugepage_shift;
>> +	for (i = 0; i < pte_num; i++, ptep++, addr += (1 << hugepage_shift))
>>   		set_pte_at(mm, addr, ptep, pte);
>>   }
>>   
>> -- 
>> 2.39.2
>>
>>
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>> linux-riscv@...ts.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-riscv
>>
>> _______________________________________________
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