[RFC/PATCH 3/7] ARM: ARM11 MPCore: {clean, flush}_pmd_entry are not preempt safe

[George G. Davis]

On Oct 13, 2011, at 10:31 AM, Russell King - ARM Linux wrote:

> On Tue, Oct 11, 2011 at 10:34:17PM -0400, George G. Davis wrote:
>> 
>> On Oct 11, 2011, at 5:53 AM, Catalin Marinas wrote:
>> 
>>> On Fri, Oct 07, 2011 at 03:38:37AM +0100, gdavis at mvista.com wrote:
>>>> diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
>>>> index 594d677..3c8253f 100644
>>>> --- a/arch/arm/mm/mmu.c
>>>> +++ b/arch/arm/mm/mmu.c
>>>> @@ -567,12 +567,24 @@ static void __init alloc_init_section(pud_t *pud, unsigned long addr,
>>>> 		if (addr & SECTION_SIZE)
>>>> 			pmd++;
>>>> 
>>>> +		if (cache_ops_need_broadcast())
>>>> +			preempt_disable();
>>>> 		do {
>>>> 			*pmd = __pmd(phys | type->prot_sect);
>>>> 			phys += SECTION_SIZE;
>>>> 		} while (pmd++, addr += SECTION_SIZE, addr != end);
>>>> 
>>>> +		/* FIXME: Multiple PMD entries may be written above
>>>> +		 * but only one cache line, up to 8 PMDs depending
>>>> +		 * on the alignment of this mapping, is flushed below.
>>>> +		 * IFF this mapping spans >8MiB, then only the first
>>>> +		 * 8MiB worth of entries will be flushed.  Entries
>>>> +		 * above the 8MiB limit will not be flushed if I
>>>> +		 * read this correctly.
>>>> +		 */
>>>> 		flush_pmd_entry(p);
>>>> +		if (cache_ops_need_broadcast())
>>>> +			preempt_enable();
>>> 
>>> My reading of the create_mapping() code is that alloc_init_pud() and
>>> alloc_init_section() are called with a 2MB range only (that's 2
>>> entries) given by pgd_addr_end().
>> 
>> You're correct of course.  I initially stuck that FIXME note in there more as
>> a reminder to review it more carefully.  Alas, in my haste, I submitted as-is
>> w/o checking parameter bounds passed from callers which do as you
>> say, so it's never more than 2MiB in size.  Thanks for the feedback.
>> I'll remove that note.
> 
> Note also that the early bringup of MMU mappings (alloc_init_section
> etc) are running before SMP bringup, so they're already bound to a
> single CPU.  So these shouldn't need 'fixing'.

Yep, I knew that and just went ahead and used a shot gun anyway.  I'll
drop cases which are already safe.

Thanks!

--
Regards,
George