Re: [PATCH v12 4/5] arm64: Implement page table free interfaces

[Chintan Pandya]

On 6/4/2018 5:43 PM, Will Deacon wrote:
> On Fri, Jun 01, 2018 at 06:09:17PM +0530, Chintan Pandya wrote:
> > Implement pud_free_pmd_page() and pmd_free_pte_page().
> >
> > Implementation requires,
> >   1) Clearing off the current pud/pmd entry
> >   2) Invalidate TLB which could have previously
> >      valid but not stale entry
> >   3) Freeing of the un-used next level page tables
>
> Please can you rewrite this describing the problem that you're solving,
> rather than a brief summary of some requirements?

Okay. I'll fix this in v13.

> > Signed-off-by: Chintan Pandya <cpandya@xxxxxxxxxxxxxx>
> > ---
> >   arch/arm64/mm/mmu.c | 38 ++++++++++++++++++++++++++++++++++----
> >   1 file changed, 34 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> > index 8ae5d7a..6e7e16c 100644
> > --- a/arch/arm64/mm/mmu.c
> > +++ b/arch/arm64/mm/mmu.c
> > @@ -45,6 +45,7 @@
> >   #include <asm/memblock.h>
> >   #include <asm/mmu_context.h>
> >   #include <asm/ptdump.h>
> > +#include <asm/tlbflush.h>
> >   
> >   #define NO_BLOCK_MAPPINGS	BIT(0)
> >   #define NO_CONT_MAPPINGS	BIT(1)
> > @@ -977,12 +978,41 @@ int pmd_clear_huge(pmd_t *pmdp)
> >   	return 1;
> >   }
> >   
> > -int pud_free_pmd_page(pud_t *pud, unsigned long addr)
> > +int pmd_free_pte_page(pmd_t *pmdp, unsigned long addr)
> >   {
> > -	return pud_none(*pud);
> > +	pte_t *table;
> > +	pmd_t pmd;
> > +
> > +	pmd = READ_ONCE(*pmdp);
> > +	if (pmd_present(pmd)) {
> > +		table = pmd_page_vaddr(pmd);
> > +		pmd_clear(pmdp);
> > +		__flush_tlb_kernel_pgtable(addr);
> > +		pte_free_kernel(NULL, table);
> > +	}
> > +	return 1;
> >   }
> >   
> > -int pmd_free_pte_page(pmd_t *pmd, unsigned long addr)
> > +int pud_free_pmd_page(pud_t *pudp, unsigned long addr)
> >   {
> > -	return pmd_none(*pmd);
> > +	pmd_t *table;
> > +	pmd_t *entry;
> > +	pud_t pud;
> > +	unsigned long next, end;
> > +
> > +	pud = READ_ONCE(*pudp);
> > +	if (pud_present(pud)) {
>
> Just some stylistic stuff, but please can you rewrite this as:
>
> 	if (!pud_present(pud) || VM_WARN_ON(!pud_table(pud)))
> 		return 1;
>
> similarly for the pmd/pte code above.

Okay. v13 will have this.

> > +		table = pud_page_vaddr(pud);
> > +		entry = table;
>
> Could you rename entry -> pmdp, please?

Sure.

> > +		next = addr;
> > +		end = addr + PUD_SIZE;
> > +		do {
> > +			pmd_free_pte_page(entry, next);
> > +		} while (entry++, next += PMD_SIZE, next != end);
> > +
> > +		pud_clear(pudp);
> > +		__flush_tlb_kernel_pgtable(addr);
> > +		pmd_free(NULL, table);
> > +	}
> > +	return 1;
>
> So with these patches, we only ever return 1 from these helpers. It looks
> like the same is true for x86, so how about we make them void and move the
> calls inside the conditionals in lib/ioremap.c? Obviously, this would be a
> separate patch on the end.

That sounds valid code churn to me. But since x86 discussion is not
concluded yet, I would wait to share until that gets resolved. May be
not in v13 but separate effort. Would that be okay to you ?

> Will

Chintan
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