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

[linux@arm.linux.org.uk (Russell King - ARM Linux)]

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'.