Re: [PATCH] x86/e820: discard high memory that can't be addressed by 32-bit systems

[Ingo Molnar]

* Nathan Chancellor <nathan@xxxxxxxxxx> wrote:

> Hi Mike,
> 
> On Sun, Apr 13, 2025 at 11:08:58AM +0300, Mike Rapoport wrote:
> ...
> >  arch/x86/kernel/e820.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
> > index 57120f0749cc..5f673bd6c7d7 100644
> > --- a/arch/x86/kernel/e820.c
> > +++ b/arch/x86/kernel/e820.c
> > @@ -1300,6 +1300,14 @@ void __init e820__memblock_setup(void)
> >  		memblock_add(entry->addr, entry->size);
> >  	}
> >  
> > +	/*
> > +	 * 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);
> > +
> >  	/* Throw away partial pages: */
> >  	memblock_trim_memory(PAGE_SIZE);
> 
> Our CI noticed a boot failure after this change as commit 1e07b9fad022
> ("x86/e820: Discard high memory that can't be addressed by 32-bit
> systems") in -tip when booting i386_defconfig with a simple buildroot
> initrd.

I've zapped this commit from tip:x86/urgent for the time being:

  1e07b9fad022 ("x86/e820: Discard high memory that can't be addressed by 32-bit systems")

until these bugs are better understood.

Thanks,

	Ingo