On Wed, Dec 23, 2020 at 08:35:37AM -0800, Roman Gushchin wrote:
> On Tue, Dec 22, 2020 at 08:06:06PM -0800, Andrew Morton wrote:
> > On Mon, 21 Dec 2020 09:05:51 -0800 Roman Gushchin <guro@xxxxxx> wrote:
> >
> > > Subject: [PATCH v3 1/2] mm: cma: allocate cma areas bottom-up
> >
> > i386 allmodconfig:
> >
> > In file included from ./include/vdso/const.h:5,
> > from ./include/linux/const.h:4,
> > from ./include/linux/bits.h:5,
> > from ./include/linux/bitops.h:6,
> > from ./include/linux/kernel.h:11,
> > from ./include/asm-generic/bug.h:20,
> > from ./arch/x86/include/asm/bug.h:93,
> > from ./include/linux/bug.h:5,
> > from ./include/linux/mmdebug.h:5,
> > from ./include/linux/mm.h:9,
> > from ./include/linux/memblock.h:13,
> > from mm/cma.c:24:
> > mm/cma.c: In function ‘cma_declare_contiguous_nid’:
> > ./include/uapi/linux/const.h:20:19: warning: conversion from ‘long long unsigned int’ to ‘phys_addr_t’ {aka ‘unsigned int’} changes value from ‘4294967296’ to ‘0’ [-Woverflow]
> > #define __AC(X,Y) (X##Y)
> > ^~~~~~
> > ./include/uapi/linux/const.h:21:18: note: in expansion of macro ‘__AC’
> > #define _AC(X,Y) __AC(X,Y)
> > ^~~~
> > ./include/linux/sizes.h:46:18: note: in expansion of macro ‘_AC’
> > #define SZ_4G _AC(0x100000000, ULL)
> > ^~~
> > mm/cma.c:349:53: note: in expansion of macro ‘SZ_4G’
> > addr = memblock_alloc_range_nid(size, alignment, SZ_4G,
> > ^~~~~
> >
>
> I thought that (!memblock_bottom_up() && memblock_end >= SZ_4G + size)
> can't be true on a 32-bit platform, so the whole if clause can be compiled out.
> Maybe it's because memblock_end can be equal to SZ_4G and if the size == 0...
>
> I have no better idea than wrapping everything into
> #if BITS_PER_LONG > 32
> #endif.
32-bit systems can have more than 32 bit in the physical address.
I think a better option would be to use CONFIG_PHYS_ADDR_T_64BIT
> Thanks!
>
> --
>
> diff --git a/mm/cma.c b/mm/cma.c
> index 4fe74c9d83b0..5d69b498603a 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -344,12 +344,14 @@ int __init cma_declare_contiguous_nid(phys_addr_t base,
> * Avoid using first 4GB to not interfere with constrained zones
> * like DMA/DMA32.
> */
> +#if BITS_PER_LONG > 32
> if (!memblock_bottom_up() && memblock_end >= SZ_4G + size) {
> memblock_set_bottom_up(true);
> addr = memblock_alloc_range_nid(size, alignment, SZ_4G,
> limit, nid, true);
> memblock_set_bottom_up(false);
> }
> +#endif
>
> if (!addr) {
> addr = memblock_alloc_range_nid(size, alignment, base,
--
Sincerely yours,
Mike.
