[PATCH] x86/coreboot: Exclude memory regions starting above 4GB

[Tom Rini]

On Thu, Feb 05, 2026 at 10:50:24AM -0700, Jeremy Compostella wrote:

> Is there anything more I should be doing? This is a bug fix I would really appreciate seeing merged.

It would be nice if someone else reviewed it. It's also been a day since
posting. I'll put it in my list to make sure doesn't get lost for the
next release, thanks.

> 
> Regards,
> Jeremy
> 
> Jeremy Compostella <jeremy.compostella at intel.com> writes:
> 
> > This commit updates the RAM region filtering logic in
> > board_get_usable_ram_top() to skip any memory regions whose start address
> > is above 4GB. Previously, only the end address was capped at 4GB, but
> > regions entirely above this threshold were still considered.
> >
> > Typically, the following memory map entries would cause
> > board_get_usable_ram_top() to return 0x100000000, which is incorrect.
> >
> >     start=00000000, end=00001000, type=16
> >     start=00001000, end=000a0000, type=1
> >     start=000a0000, end=000f6000, type=2
> >     start=000f6000, end=000f7000, type=16
> >     start=000f7000, end=00100000, type=2
> >     start=00100000, end=6f170000, type=1
> >     start=6f170000, end=70000000, type=16
> >     start=70000000, end=80800000, type=2
> >     start=e0000000, end=f8000000, type=2
> >     start=fa000000, end=fc000000, type=2
> >     start=fc800000, end=fc880000, type=2
> >     start=fd800000, end=fe800000, type=2
> >     start=feb00000, end=feb80000, type=2
> >     start=fec00000, end=fed00000, type=2
> >     start=fed20000, end=fed80000, type=2
> >     start=feda1000, end=feda2000, type=2
> >     start=fedc0000, end=fede0000, type=2
> >     start=100000000, end=102400000, type=2
> >     start=102400000, end=47f800000, type=1
> >     start=4000000000, end=4020000000, type=2
> >
> > By adding a check to continue the loop if the region's start address
> > exceeds 0xffffffffULL, the function now properly ignores regions that are
> > not usable in 32-bit address space.
> >
> > Change-Id: I8cbe0281aeea67a2f5bb9f6669456f5c7df9b409
> > Signed-off-by: Jeremy Compostella <jeremy.compostella at intel.com>
> > ---
> >  arch/x86/cpu/coreboot/sdram.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/arch/x86/cpu/coreboot/sdram.c b/arch/x86/cpu/coreboot/sdram.c
> > index 013225f129a..cc1edd7badd 100644
> > --- a/arch/x86/cpu/coreboot/sdram.c
> > +++ b/arch/x86/cpu/coreboot/sdram.c
> > @@ -42,6 +42,8 @@ phys_addr_t board_get_usable_ram_top(phys_size_t total_size)
> >  			continue;
> >  
> >  		/* Filter memory over 4GB. */
> > +		if (start > 0xffffffffULL)
> > +			continue;
> >  		if (end > 0xffffffffULL)
> >  			end = 0x100000000ULL;
> >  		/* Skip this region if it's too small. */
> 
> -- 
> Jeremy
> One Emacs to rule them all

-- 
Tom
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