Re: [PATCH v3 1/3] resource: Add @flags to region_intersects()

From: Toshi Kani
Date: Thu Dec 03 2015 - 14:40:31 EST


On Thu, 2015-12-03 at 11:01 -0800, Linus Torvalds wrote:
> On Thu, Dec 3, 2015 at 10:40 AM, Borislav Petkov <bp@xxxxxxxxx> wrote:
> > On Thu, Dec 03, 2015 at 11:54:19AM -0700, Toshi Kani wrote:
> > > Adding a new type for regular memory will require inspecting the
> > > codes using IORESOURCE_MEM currently, and modify them to use the new
> > > type if their target ranges are regular memory. There are many
> > > references to this type across multiple architectures and drivers,
> > > which make this inspection and testing challenging.
> >
> > What's wrong with adding a new type_flags to struct resource and not
> > touching IORESOURCE_* at all?
>
> Bah. Both of these ideas are bogus.
>
> Just add a new flag. The bits are already modifiers that you can
> *combine* to show what kind of resource it is, and we already have
> things like IORESOURCE_PREFETCH etc, that are in *addition* to the
> normal IORESOURCE_MEM bit.
>
> Just add another modifier: IORESOURCE_RAM.
>
> So it would still show up as IORESOURCE_MEM, but it would have
> additional information specifying that it's actually RAM.
>
> If somebody does something like
>
> if (res->flags == IORESOURCE_MEM)
>
> then they are already completely broken and won't work *anyway*. It's
> a bitmask, bit a set of values.

Yes, if we can assign new modifiers, that will be quite simple. :-) I
assume we can allocate new bits from the remaining free bits as follows.

+#define IORESOURCE_SYSTEM_RAM 0x01000000 /* System RAM */
+#define IORESOURCE_PMEM 0x02000000 /* Persistent memory */
#define IORESOURCE_EXCLUSIVE 0x08000000 /* Userland may not map
this resource */

Note, SYSTEM_RAM represents the OS memory, i.e. "System RAM", not any RAM
ranges.

With the new modifiers, region_intersect() can check these ranges. One
caveat is that the modifiers are not very extensible for new types as they
are bit maps. region_intersect() will no longer be capable of checking any
regions with any given name. I think this is OK since this function was
introduced recently, and is only used for checking "System RAM" and
"Persistent Memory" (with this patch series).

Thanks,
-Toshi
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