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

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Date:	Wed, 6 Feb 2013 11:07:07 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Rob Herring <robherring2@...il.com>
Cc:	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Rob Herring <rob.herring@...xeda.com>,
	Russell King <linux@....linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5 3/3] ARM: mm: use static_vm for managing static mapped
 areas

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@....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.
But, I think that it is not an error.
Now, I see your original commit 'c2794437091a4fda72c4a4f3567dd728dcc0c3c9'
and find below message.

"Platforms which need early i/o mapping (e.g. for vga console) can call
pci_map_io_early in their .map_io function."

Therfore, for some platform, it is possible that there is a mapping within
PCI reserved range.

So, I will not add WARN here.

I will fix and re-send v6 with your ACK.

Thanks for review.

> >>>
> >>> 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.
> 
> Ah, right. In that case:
> 
> Acked-by: Rob Herring <rob.herring@...xeda.com>
> 
> Rob
> 
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