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Date: Fri, 18 Apr 2025 08:33:02 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Nathan Chancellor <nathan@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>, Andy Shevchenko <andy@kernel.org>,
	Arnd Bergmann <arnd@arndb.de>, Arnd Bergmann <arnd@kernel.org>,
	Borislav Petkov <bp@alien8.de>, Dave Hansen <dave.hansen@intel.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Davide Ciminaghi <ciminaghi@gnudd.com>,
	Ingo Molnar <mingo@redhat.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Matthew Wilcox <willy@infradead.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	Thomas Gleixner <tglx@linutronix.de>, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org, x86@kernel.org
Subject: Re: [PATCH] x86/e820: discard high memory that can't be addressed by
 32-bit systems
Message-ID: <aAHyHuwbmhjWmDqc@gmail.com>
References: <Z_rDdnlSs0rts3b9@gmail.com>
 <20250413080858.743221-1-rppt@kernel.org>
 <20250417162206.GA104424@ax162>
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* Nathan Chancellor <nathan@kernel.org> 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