From: Bibo Mao <maobibo@loongson.cn>
To: Tianyang Zhang <zhangtianyang@loongson.cn>,
chenhuacai@kernel.org, kernel@xen0n.name,
akpm@linux-foundation.org, willy@infradead.org, david@redhat.com,
linmag7@gmail.com, thuth@redhat.com, apopple@nvidia.com
Cc: loongarch@lists.linux.dev, linux-kernel@vger.kernel.org,
Liupu Wang <wangliupu@loongson.cn>
Subject: Re: [PATCH] Loongarch:Make pte/pmd_modify can set _PAGE_MODIFIED
Date: Wed, 8 Apr 2026 16:10:58 +0800 [thread overview]
Message-ID: <db75dcb9-25ab-ddea-f00f-c4322c867a63@loongson.cn> (raw)
In-Reply-To: <721fdf6e-61c4-2e31-c584-04d8380f2952@loongson.cn>
On 2025/11/6 下午5:53, Tianyang Zhang wrote:
>
> 在 2025/11/6 下午3:07, Bibo Mao 写道:
>>
>>
>> On 2025/11/4 下午3:30, Tianyang Zhang wrote:
>>> In the current pte_modify operation, _PAGE_DIRTY might be cleared. Since
>>> the hardware-page-walk does not have a predefined _PAGE_MODIFIED flag,
>>> this could lead to loss of valid data in certain scenarios.
>>>
>>> The new modification involves checking whether the original PTE has the
>>> _PAGE_DIRTY flag. If it exists, the _PAGE_MODIFIED bit is set, ensuring
>>> that the pte_dirty interface can return accurate information.
>>>
>>> Co-developed-by: Liupu Wang <wangliupu@loongson.cn>
>>> Signed-off-by: Liupu Wang <wangliupu@loongson.cn>
>>> Signed-off-by: Tianyang Zhang <zhangtianyang@loongson.cn>
>>> ---
>>> arch/loongarch/include/asm/pgtable.h | 17 +++++++++++++----
>>> 1 file changed, 13 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/arch/loongarch/include/asm/pgtable.h
>>> b/arch/loongarch/include/asm/pgtable.h
>>> index bd128696e96d..106abfa5183b 100644
>>> --- a/arch/loongarch/include/asm/pgtable.h
>>> +++ b/arch/loongarch/include/asm/pgtable.h
>>> @@ -424,8 +424,13 @@ static inline unsigned long
>>> pte_accessible(struct mm_struct *mm, pte_t a)
>>> static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
>>> {
>>> - return __pte((pte_val(pte) & _PAGE_CHG_MASK) |
>>> - (pgprot_val(newprot) & ~_PAGE_CHG_MASK));
>>> + unsigned long val = (pte_val(pte) & _PAGE_CHG_MASK) |
>>> + (pgprot_val(newprot) & ~_PAGE_CHG_MASK);
>>> +
>>> + if (pte_val(pte) & _PAGE_DIRTY)
>>> + val |= _PAGE_MODIFIED;
>> Since ptep_get_and_clear() is not atomic operation on LoongArch like
>> other architectures, considering this scenery with HW PTW enabled:
>> CPU 0: CPU1
>> old_pte = ptep_modify_prot_start();
>> old_pte = ptep_get(ptep);
>>
>> write(buf);
>> *HW will set _PAGE_DIRTY bit*
>> pte_clear(mm, address, ptep);
>> ^^^^^^^^^^ For CPU1, bit _PAGE_DIRTY is no set in old_pte, _PAGE_DIRTY
>> will be lost also. ^^^^^^^^^^^
>> pte = pte_modify(old_pte,)
>> ptep_modify_prot_commit(.., pte)
>
> There does appear to be an issue here. It seems we should use
> `__HAVE_ARCH_PTEP_GET_AND_CLEAR` and implement ptep_get_and_clear via
> `atomic_xchg`.
>
> However, I believe this change should be submitted in a new patch.
What is the status about API ptep_get_and_clear() on LoongArch?
Regards
Bibo Mao
>
> Thanks
>
> Tianyang
>
>>
>> Regards
>> Bibo Mao
>>> +
>>> + return __pte(val);
>>> }
>>> extern void __update_tlb(struct vm_area_struct *vma,
>>> @@ -547,9 +552,13 @@ static inline struct page *pmd_page(pmd_t pmd)
>>> static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
>>> {
>>> - pmd_val(pmd) = (pmd_val(pmd) & _HPAGE_CHG_MASK) |
>>> + unsigned long val = (pmd_val(pmd) & _HPAGE_CHG_MASK) |
>>> (pgprot_val(newprot) & ~_HPAGE_CHG_MASK);
>>> - return pmd;
>>> +
>>> + if (pmd_val(pmd) & _PAGE_DIRTY)
>>> + val |= _PAGE_MODIFIED;
>>> +
>>> + return __pmd(val);
>>> }
>>> static inline pmd_t pmd_mkinvalid(pmd_t pmd)
>>>
prev parent reply other threads:[~2026-04-08 8:13 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-11-04 7:30 [PATCH] Loongarch:Make pte/pmd_modify can set _PAGE_MODIFIED Tianyang Zhang
2025-11-04 8:00 ` Huacai Chen
2025-11-05 0:56 ` Tianyang Zhang
2025-11-05 1:07 ` Huacai Chen
2025-11-05 1:18 ` Bibo Mao
2025-11-06 1:55 ` Tianyang Zhang
2025-11-06 2:10 ` Bibo Mao
2025-11-06 8:50 ` Tianyang Zhang
2025-11-06 9:02 ` Bibo Mao
2025-11-06 7:07 ` Bibo Mao
2025-11-06 9:53 ` Tianyang Zhang
2026-04-08 8:10 ` Bibo Mao [this message]
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