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

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Date:	Thu, 13 Feb 2014 11:52:03 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Russell King <linux@....linux.org.uk>,
	Will Deacon <Will.Deacon@....com>,
	Steven Capper <steve.capper@...aro.org>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Laura Abbott <lauraa@...eaurora.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] ARM: mm: report both sections from PMD

On Thu, Feb 13, 2014 at 9:12 AM, Catalin Marinas
<catalin.marinas@....com> 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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