Re: [PATCH] RISC-V: Don't have MAX_PHYSMEM_BITS exceed phys_addr_t

[Charlie Jenkins <charlie@rivosinc.com>]

On Wed, Jul 31, 2024 at 09:22:00AM -0700, Palmer Dabbelt wrote:
> I recently ended up with a warning on some compilers along the lines of
> 
>       CC      kernel/resource.o
>     In file included from include/linux/ioport.h:16,
>                      from kernel/resource.c:15:
>     kernel/resource.c: In function 'gfr_start':
>     include/linux/minmax.h:49:37: error: conversion from 'long long unsigned int' to 'resource_size_t' {aka 'unsigned int'} changes value from '17179869183' to '4294967295' [-Werror=overflow]
>        49 |         ({ type ux = (x); type uy = (y); __cmp(op, ux, uy); })
>           |                                     ^
>     include/linux/minmax.h:52:9: note: in expansion of macro '__cmp_once_unique'
>        52 |         __cmp_once_unique(op, type, x, y, __UNIQUE_ID(x_), __UNIQUE_ID(y_))
>           |         ^~~~~~~~~~~~~~~~~
>     include/linux/minmax.h:161:27: note: in expansion of macro '__cmp_once'
>       161 | #define min_t(type, x, y) __cmp_once(min, type, x, y)
>           |                           ^~~~~~~~~~
>     kernel/resource.c:1829:23: note: in expansion of macro 'min_t'
>      1829 |                 end = min_t(resource_size_t, base->end,
>           |                       ^~~~~
>     kernel/resource.c: In function 'gfr_continue':
>     include/linux/minmax.h:49:37: error: conversion from 'long long unsigned int' to 'resource_size_t' {aka 'unsigned int'} changes value from '17179869183' to '4294967295' [-Werror=overflow]
>        49 |         ({ type ux = (x); type uy = (y); __cmp(op, ux, uy); })
>           |                                     ^
>     include/linux/minmax.h:52:9: note: in expansion of macro '__cmp_once_unique'
>        52 |         __cmp_once_unique(op, type, x, y, __UNIQUE_ID(x_), __UNIQUE_ID(y_))
>           |         ^~~~~~~~~~~~~~~~~
>     include/linux/minmax.h:161:27: note: in expansion of macro '__cmp_once'
>       161 | #define min_t(type, x, y) __cmp_once(min, type, x, y)
>           |                           ^~~~~~~~~~
>     kernel/resource.c:1847:24: note: in expansion of macro 'min_t'
>      1847 |                addr <= min_t(resource_size_t, base->end,
>           |                        ^~~~~
>     cc1: all warnings being treated as errors
> 
> which looks like a real problem: our phys_addr_t is only 32 bits now, so
> having 34-bit masks is just going to result in overflows.
> 
> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
> ---
> This is sort of a v2 of
> https://lore.kernel.org/r/20240729151652.15063-2-palmer@rivosinc.com,
> but I think that was just bogus.
> ---
>  arch/riscv/include/asm/sparsemem.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/include/asm/sparsemem.h b/arch/riscv/include/asm/sparsemem.h
> index 63acaecc3374..2f901a410586 100644
> --- a/arch/riscv/include/asm/sparsemem.h
> +++ b/arch/riscv/include/asm/sparsemem.h
> @@ -7,7 +7,7 @@
>  #ifdef CONFIG_64BIT
>  #define MAX_PHYSMEM_BITS	56
>  #else
> -#define MAX_PHYSMEM_BITS	34

I was trying to figure out why this was set to 34. It looks like that
comes from this patch (which heavily changed over the course of review)
[1] and the following text:

"On the Sifive hardware this allows us to provide struct pages for
the lower I/O TileLink address ranges, the 32-bit and 34-bit DRAM areas
and 172GB of 240GB of the high I/O TileLink region. Once we progress to
Sv48 we should be able to cover all the available memory regions."

Seems like the max should be 32 though so:

Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>

Link: https://lore.kernel.org/all/20190327213643.23789-4-logang@deltatee.com/ [1]


> +#define MAX_PHYSMEM_BITS	32
>  #endif /* CONFIG_64BIT */
>  #define SECTION_SIZE_BITS	27
>  #endif /* CONFIG_SPARSEMEM */
> -- 
> 2.45.2
> 
> 
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