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SubjectRe: [PATCH] ARM: allow, but warn, when issuing ioremap() on RAM
On Fri, Oct 08, 2010 at 10:41:42PM -0400, Nicolas Pitre wrote:
> On Sat, 9 Oct 2010, Russell King - ARM Linux wrote:
>
> > On Fri, Oct 08, 2010 at 05:00:46PM -0700, Greg KH wrote:
> > > But you can't expect that you make this change, and not fix up the
> > > drivers, and people would be happy, right? The rule for API changes
> > > like this, or anything, is that the person making the change fixes the
> > > other drivers, and that seems to be the issue here.
> >
> > Let's entirely revert the change and wait for people's data to be
> > corrupted then. I don't have the time nor the motivation to work
> > through crap driver code to fix up these unreliable games which are
> > already illegal on platforms such as x86.
> >
> > If people want their system to be unpredictable, then let's carry on
> > giving them the rope to hang themselves in that manner.
> >
> > > Any pointers to patches where people have fixed up the drivers?
> >
> > Despite the discussion, I'm unaware of anyone really taking the issue
> > seriously and producing any patches during the last six months.
> >
> > So, I say sod it, let's revert the change.
>
> I think that the real issue here is to avoid breaking those drivers
> which were using this legitimately. So what about this compromize
> instead:
>
> diff --git a/arch/arm/mm/ioremap.c b/arch/arm/mm/ioremap.c
> index 99627d3..4f071e4 100644
> --- a/arch/arm/mm/ioremap.c
> +++ b/arch/arm/mm/ioremap.c
> @@ -201,6 +201,15 @@ void __iomem * __arm_ioremap_pfn_caller(unsigned long pfn,
> if (pfn >= 0x100000 && (__pfn_to_phys(pfn) & ~SUPERSECTION_MASK))
> return NULL;
>
> + /*
> + * Warn if RAM is mapped to discourage this usage. Let's forbid it
> + * outright on ARMv6+ where this became architecturally undefined
> + * in theory and causes memory corruption in practice.
> + */
> + if (WARN_ON(pfn_valid(pfn)))
> + if (__LINUX_ARM_ARCH__ >= 6)
> + return NULL;
> +
> type = get_mem_type(mtype);
> if (!type)
> return NULL;
>

That looks good to me, anyone else object to this?

Now we also need a way to fix the drivers for real on ARMv6+ now...

thanks,

greg k-h


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