Re: [PATCH v9 3/4] arm64: Implement page table free interfaces

[Chintan Pandya]

On 5/23/2018 7:31 PM, Will Deacon wrote:
> Hi Chintan,

Hi Will,

> [as a side note: I'm confused on the status of this patch series, as part
>   of it was reposted separately by Toshi. Please can you work together?]

I will share all 4 patches once again as v10 and take latest version of
1/4 as updated by Toshi.

> On Mon, Apr 30, 2018 at 01:11:33PM +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
> >
> > Signed-off-by: Chintan Pandya <cpandya@xxxxxxxxxxxxxx>
> > ---
> >   arch/arm64/mm/mmu.c | 29 +++++++++++++++++++++++++----
> >   1 file changed, 25 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> > index da98828..0f651db 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)
> > @@ -973,12 +974,32 @@ 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);
> > +	pmd_t *table;
> > +
> > +	if (pmd_present(READ_ONCE(*pmdp))) {
>
> Might also be worth checking pmd_table here, just in case. (same for pud)

I had that check in v2 as below.

if (pud_val(*pud) && !pud_huge(*pud))

But removed that in v3 as unmap should change this to NONE if it is
not table. I still don't see the need of it.

> > +		table = __va(pmd_val(*pmdp));
>
> Can you avoid dereferencing *pmdp twice, and instead READ_ONCE into a local
> variable, please? (same for pud)

Okay.

> > +		pmd_clear(pmdp);
> > +		__flush_tlb_kernel_pgtable(addr);
> > +		free_page((unsigned long) table);
>
> Shouldn't this be pte_free_kernel, to pair with pte_alloc_kernel which
> was used to allocate the page in the first place? (similarly for pud)

Okay.

> > +	}
> > +	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;
> > +	int i;
> > +
> > +	if (pud_present(READ_ONCE(*pudp))) {
> > +		table = __va(pud_val(*pudp));
> > +		for (i = 0; i < PTRS_PER_PMD; i++)
> > +			pmd_free_pte_page(&table[i], addr + (i * PMD_SIZE));
>
> I think it would be cleaner to write this as a do { ... } while, for
> consistency with the ioremap and vmalloc code.

Okay.

I'll raise v10 fixing above things. Thanks for the review.

> Will
>
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Chintan
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