Re: [PATCH v2] ARM: mm: report both sections from PMD

From: Kees Cook
Date: Thu Feb 13 2014 - 14:52:13 EST


On Thu, Feb 13, 2014 at 9:12 AM, Catalin Marinas
<catalin.marinas@xxxxxxx> wrote:
> On Wed, Feb 12, 2014 at 10:46:38PM +0000, Kees Cook wrote:
>> diff --git a/arch/arm/include/asm/pgtable-3level.h b/arch/arm/include/asm/pgtable-3level.h
>> index 03243f7eeddf..fb3de59ee811 100644
>> --- a/arch/arm/include/asm/pgtable-3level.h
>> +++ b/arch/arm/include/asm/pgtable-3level.h
>> @@ -138,10 +138,6 @@
>> #define pud_none(pud) (!pud_val(pud))
>> #define pud_bad(pud) (!(pud_val(pud) & 2))
>> #define pud_present(pud) (pud_val(pud))
>> -#define pmd_table(pmd) ((pmd_val(pmd) & PMD_TYPE_MASK) == \
>> - PMD_TYPE_TABLE)
>> -#define pmd_sect(pmd) ((pmd_val(pmd) & PMD_TYPE_MASK) == \
>> - PMD_TYPE_SECT)
>> #define pmd_large(pmd) pmd_sect(pmd)
>>
>> #define pud_clear(pudp) \
>> diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
>> index 7d59b524f2af..934aa5b60c7c 100644
>> --- a/arch/arm/include/asm/pgtable.h
>> +++ b/arch/arm/include/asm/pgtable.h
>> @@ -183,6 +183,10 @@ extern pgd_t swapper_pg_dir[PTRS_PER_PGD];
>>
>> #define pmd_none(pmd) (!pmd_val(pmd))
>> #define pmd_present(pmd) (pmd_val(pmd))
>> +#define pmd_table(pmd) ((pmd_val(pmd) & PMD_TYPE_MASK) == \
>> + PMD_TYPE_TABLE)
>> +#define pmd_sect(pmd) ((pmd_val(pmd) & PMD_TYPE_MASK) == \
>> + PMD_TYPE_SECT)
>
> Do you still need to move these two if you only use pmd_large()? AFAICT,
> it is equivalent to pmd_sect().

Why does pmd_sect exist? I can reduce it to just using pmd_large.

>
>> static inline pte_t *pmd_page_vaddr(pmd_t pmd)
>> {
>> diff --git a/arch/arm/mm/dump.c b/arch/arm/mm/dump.c
>> index 2b342177f5de..32635b474832 100644
>> --- a/arch/arm/mm/dump.c
>> +++ b/arch/arm/mm/dump.c
>> @@ -260,8 +260,14 @@ static void walk_pmd(struct pg_state *st, pud_t *pud, unsigned long start)
>>
>> for (i = 0; i < PTRS_PER_PMD; i++, pmd++) {
>> addr = start + i * PMD_SIZE;
>> - if (pmd_none(*pmd) || pmd_large(*pmd) || !pmd_present(*pmd))
>> + if (pmd_none(*pmd) || pmd_large(*pmd) || !pmd_present(*pmd)) {
>> note_page(st, addr, 3, pmd_val(*pmd));
>> + if (SECTION_SIZE < PMD_SIZE &&
>> + pmd_sect(*pmd) && pmd_sect(pmd[1])) {
>
> I think the first patch was better with pmd[0] and pmd[1] treated
> independently if SECTION_SIZE < PMD_SIZE, only that it should have
> checked for pmd_sect(pmd[1]). I don't see anything in
> __map_init_section() that would prevent populating only the second pmd
> leaving the first one empty.

Ah, gotcha. Okay, I will send a new version. Thanks!

-Kees

--
Kees Cook
Chrome OS Security
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