Re: [PATCH 03/03] fbdev: maxine: fix 64-bit build error

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] `smem_start` is incorrectly populated with a virtual address instead of a physical address, which breaks user-space mmap.
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--- Patch [3]: [PATCH 03/03] fbdev: maxine: fix 64-bit build error ---
commit 4b24e26365b585612a868800c1d954fcade38bb4
Author: Randy Dunlap <rdunlap@infradead.org>
fbdev: maxine: fix 64-bit build error

This commit resolves a 64-bit build error in the maxinefb driver by
replacing the KSEG1ADDR() macro, which is only defined for non-64BIT
builds, with the CKSEG1ADDR() macro.

> diff --git a/include/video/maxinefb.h b/include/video/maxinefb.h
> index 6aeb4acca2bdb..2b66b32f355cf 100644
> --- a/include/video/maxinefb.h
> +++ b/include/video/maxinefb.h
[ ... ]
> @@ -19,7 +19,7 @@
>  /*
>   * Begin of DECstation 5000/xx onboard framebuffer memory, default resolution
>   * is 1024x768x8
>   */
> -#define DS5000_xx_ONBOARD_FBMEM_START	KSEG1ADDR(0x0a000000)
> +#define DS5000_xx_ONBOARD_FBMEM_START	CKSEG1ADDR(0x0a000000)

[Severity: High]
This is a pre-existing issue, but does assigning this virtual address to
the framebuffer's fix.smem_start break user-space mmap?

When user-space applications call mmap() on the framebuffer device, fb_mmap 
calculates the physical frame number by shifting info->fix.smem_start. Since 
this macro defines a virtual CKSEG1 address instead of a physical address 
(0x0a000000), the resulting physical frame number maps to invalid physical 
memory space.

Looking at drivers/video/fbdev/maxinefb.c in maxinefb_init():

    fb_start = DS5000_xx_ONBOARD_FBMEM_START;
    ...
    maxinefb_fix.smem_start = fb_start;

Should smem_start be populated with the actual physical address rather than
the CKSEG1-mapped virtual address to prevent bus errors or unintended physical
memory access during user-space mappings?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260813232934.2718291-1-rdunlap@infradead.org?part=3