Re: [PATCH v5 3/3] ARM: mm: use static_vm for managing static mapped areas

Nicolas Pitre
2013-02-06T06:20:05Z

On Wed, 6 Feb 2013, Joonsoo Kim wrote:

> On Wed, Feb 06, 2013 at 11:07:07AM +0900, Joonsoo Kim wrote:
> > Hello, Rob.
> >
> > On Tue, Feb 05, 2013 at 01:12:51PM -0600, Rob Herring wrote:
> > > On 02/05/2013 12:13 PM, Nicolas Pitre wrote:
> > > > On Tue, 5 Feb 2013, Rob Herring wrote:
> > > >
> > > >> On 02/04/2013 10:44 PM, Nicolas Pitre wrote:
> > > >>> On Tue, 5 Feb 2013, Joonsoo Kim wrote:
> > > >>>
> > > >>>> A static mapped area is ARM-specific, so it is better not to use
> > > >>>> generic vmalloc data structure, that is, vmlist and vmlist_lock
> > > >>>> for managing static mapped area. And it causes some needless overhead and
> > > >>>> reducing this overhead is better idea.
> > > >>>>
> > > >>>> Now, we have newly introduced static_vm infrastructure.
> > > >>>> With it, we don't need to iterate all mapped areas. Instead, we just
> > > >>>> iterate static mapped areas. It helps to reduce an overhead of finding
> > > >>>> matched area. And architecture dependency on vmalloc layer is removed,
> > > >>>> so it will help to maintainability for vmalloc layer.
> > > >>>>
> > > >>>> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> > > >>
> > > >> [snip]
> > > >>
> > > >>>> @@ -859,17 +864,12 @@ static void __init pci_reserve_io(void)
> > > >>>> {
> > > >>>> struct vm_struct *vm;
> > > >>>> unsigned long addr;
> > > >>>> + struct static_vm *svm;
> > > >>>>
> > > >>>> - /* we're still single threaded hence no lock needed here */
> > > >>>> - for (vm = vmlist; vm; vm = vm->next) {
> > > >>>> - if (!(vm->flags & VM_ARM_STATIC_MAPPING))
> > > >>>> - continue;
> > > >>>> - addr = (unsigned long)vm->addr;
> > > >>>> - addr &= ~(SZ_2M - 1);
> > > >>>> - if (addr == PCI_IO_VIRT_BASE)
> > > >>>> - return;
> > > >>>> + svm = find_static_vm_vaddr((void *)PCI_IO_VIRT_BASE);
> > > >>>> + if (svm)
> > > >>>> + return;
> > > >>>>
> > > >>>> - }
> > > >>>>
> > > >>>> vm_reserve_area_early(PCI_IO_VIRT_BASE, SZ_2M, pci_reserve_io);
> > > >>>> }
> > > >>>
> > > >>> The replacement code is not equivalent. I can't recall why the original
> > > >>> is as it is, but it doesn't look right to me. The 2MB round down
> > > >>> certainly looks suspicious.
> > > >>
> > > >> The PCI mapping is at a fixed, aligned 2MB mapping. If we find any
> > > >> virtual address within that region already mapped, it is an error.
> > > > Ah, OK. This wasn't clear looking at the code.
> > > >> We probably should have had a WARN here.
> > > >
> > > > Indeed.
> > > >
> >
> > Okay.
> > I should fix it to find any mapping within PCI reserved region.
>
> Ah...
> Above comment is my mistake.
>
> If there is a region already mapped within PCI reserved region and
> it is not found by find_static_vm_vaddr(), vm_area_add_early() hit BUG_ON().
> So, to leave find_static_vm_vaddr() is safe.

Yes. In conclusion, your patch was fine. You may remove the redundant
parents and send the whole set to Russell.

Nicolas