On Mon, Apr 14, 2025 at 07:19:02AM -0700, Dave Hansen wrote:
> On 4/13/25 02:23, tip-bot2 for Mike Rapoport (Microsoft) wrote:
> > + /*
> > + * 32-bit systems are limited to 4BG of memory even with HIGHMEM and
> > + * to even less without it.
> > + * Discard memory after max_pfn - the actual limit detected at runtime.
> > + */
> > + if (IS_ENABLED(CONFIG_X86_32))
> > + memblock_remove(PFN_PHYS(max_pfn), -1);
>
> Mike, thanks for the quick fix! I did verify that this gets my silly
> test VM booting again.
>
> The patch obviously _works_. But in the case I was hitting max_pfn was
> set MAX_NONPAE_PFN. The unfortunate part about this hunk is that it's
> far away from the related warning:
Yeah, my first instinct was to put memblock_remove() in the same 'if',
but there's no memblock there yet :)
> > if (max_pfn > MAX_NONPAE_PFN) {
> > max_pfn = MAX_NONPAE_PFN;
> > printk(KERN_WARNING MSG_HIGHMEM_TRIMMED);
> > }
>
> and it's logically doing the same thing: truncating memory at
> MAX_NONPAE_PFN.
>
> How about we reuse 'MAX_NONPAE_PFN' like this:
>
> if (IS_ENABLED(CONFIG_X86_32))
> memblock_remove(PFN_PHYS(MAX_NONPAE_PFN), -1);
>
> Would that make the connection more obvious?
Yes, that's better. Here's the updated patch:
