Re: [PATCH -next v6 5/6] arm64/mm: Enable ARCH_SUPPORTS_PAGE_TABLE_CHECK

[Tong Tiangen]

在 2022/5/5 1:26, Catalin Marinas 写道:
> On Tue, May 03, 2022 at 09:13:20AM +0800, Tong Tiangen wrote:
> > 在 2022/4/29 14:18, Anshuman Khandual 写道:
> > > On 4/26/22 13:40, Tong Tiangen wrote:
> > > > @@ -884,7 +928,11 @@ static inline pte_t ptep_get_and_clear(struct mm_struct *mm,
> > > >    static inline pmd_t pmdp_huge_get_and_clear(struct mm_struct *mm,
> > > >    					    unsigned long address, pmd_t *pmdp)
> > > >    {
> > > > -	return pte_pmd(ptep_get_and_clear(mm, address, (pte_t *)pmdp));
> > > > +	pmd_t pmd = pte_pmd(__pte(xchg_relaxed(&pte_val(*(pte_t *)pmdp), 0)));
> > >
> > > Why there is any change here ? Why not just the following instead, like what you did
> > > in ptep_get_and_clear() above. The page table entry return value here just needs to
> > > be preserved for subsequent page table check helpers.
> > >
> > > 	pmd_t pmd = pte_pmd(ptep_get_and_clear(mm, address, (pte_t *)pmdp));
> >
> > The purpose of what I do here is to avoid doing page_table_check_pte_clear()
> > in ptep_get_and_clear(). there is no functional change here.
>
> I'm fine with using xchg here but I'd go for pmd_val directly, no need
> for conversion to pte_t:
>
> 	pmd_t pmd = __pmd(xchg_relaxed(&pmd_val(*pmdp), 0));

OK, This implementation is good and avoids redundant conversion, will 
fix it next version.

Thanks,
Tong.