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

Nicolas Pitre
2013-02-05T18:13:13Z

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.

> >
> > The replacement code should be better. However I'd like you to get an
> > ACK from Rob Herring as well for this patch.
>
> It doesn't appear to me the above case is handled. The virt addr is
> checked whether it is within an existing mapping, but not whether the
> new mapping would overlap an existing mapping. It would be good to check
> for this generically rather than specifically for the PCI i/o mapping.

Agreed. However that is checked already in vm_area_add_early().
Therefore the overlap test here is redundant.

Nicolas