Messages in this thread | | | Date | Thu, 7 Aug 2008 16:27:41 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] Make PFN_PHYS return a properly-formed physical address |
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On Thu, 07 Aug 2008 15:10:11 -0700 Jeremy Fitzhardinge <jeremy@goop.org> wrote:
> Andrew Morton wrote: > > On Thu, 07 Aug 2008 14:38:08 -0700 > > Jeremy Fitzhardinge <jeremy@goop.org> wrote: > > > > > >> PFN_PHYS, as its name suggests, turns a pfn into a physical address. > >> However, it is a macro which just operates on its argument without > >> modifying its type. pfns are typed unsigned long, but an unsigned > >> long may not be long enough to hold a physical address (32-bit systems > >> with more than 32 bits of physcial address). This means that the > >> resulting address could be truncated if it doesn't fit within an > >> unsigned long. This isn't generally a problem because most users end > >> up using it for "low" memory, but there's no reason why PFN_PHYS > >> couldn't be used for any possible pfn. > >> > > > > Please copy a mailing list on patches. So you can get your titties > > toasted off ;) > > > > Oops. Forgot. > > >> Fortunately, resource_size_t is the right size, and has approximately > >> the right meaning. It's 64-bits on platforms where that's > >> appropriate, but 32-bits where the extra bits are not needed. > >> > > > > aww maaan. Hack or what? > > > > I don't know. Is it? It's what linux/ioport.h:struct resource uses to > hold "start" and "end", which presumably means its intended to hold > arbitrary physical addresses.
Yes, but resource_size_t is for IO addressing, not for memory addressing.
Lots of X86_32 machines can happily support 32-bit physical addresses for IO while needing >32 bit addresses for physical memory.
> >> #define PFN_ALIGN(x) (((unsigned long)(x) + (PAGE_SIZE - 1)) & PAGE_MASK) > >> #define PFN_UP(x) (((x) + PAGE_SIZE-1) >> PAGE_SHIFT) > >> #define PFN_DOWN(x) ((x) >> PAGE_SHIFT) > >> -#define PFN_PHYS(x) ((x) << PAGE_SHIFT) > >> +#define PFN_PHYS(x) ((resource_size_t)(x) << PAGE_SHIFT) > >> > > > > Busted on PAE with CONFIG_RESOURCES_64BIT=n, surely? > > > > Not an option: > > config X86_PAE > def_bool n > prompt "PAE (Physical Address Extension) Support" > depends on X86_32 && !HIGHMEM4G > select RESOURCES_64BIT >
err, OK, that was a bit arbitrary of us.
Oh well, scrub the above assertion.
Then again, do all architectures disallow 32-bit resource_size_t on 64-bit? And there's ppc32's CONFIG_HIGHMEM option to think about.
> And if you don't enable RESOURCES_64BIT, then I guess it's reasonable > for PFN_PHYS to discount the possibility of high pages? > > > Can we please do this properly, whatever that is? Even a dumb > > always-return-u64 would be better? > > > > I had that originally, but someone (hpa?) suggested resource_size_t. > The sad thing is that most users don't really care; they're either > 64-bit anyway, or immediately truncate the result to 32-bit. > > "Properly" would be to define a phys_addr_t which can always represent a > physical address. We have one in x86-land, but I hesitate to add it for > everyone else.
hm. It is a distinct and singular concept - it makes sense to have a specific type to represet "a physical address for memory".
> >> printk("initrd extends beyond end of memory " > >> - "(0x%08lx > 0x%08lx)\ndisabling initrd\n", > >> + "(0x%08lx > 0x%08llx)\ndisabling initrd\n", > >> INITRD_START + INITRD_SIZE, > >> PFN_PHYS(max_low_pfn)); > >> > > > > that'll generate a compile warning if m32r can set CONFIG_RESOURCES_64BIT=n. > > > > (u64) cast, I guess. >
nope ;) We don't know what type u64 has - some architectures use `unsigned long' (we might fix this soon).
For now, a full cast to `unsigned long long' is needed.
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