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

[Jeremy Compostella]

Tom Rini <trini at konsulko.com> writes:

> 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.

Thank you for looking into this. It would indeed help if someone else could review it.

>> 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

-- 
Jeremy
One Emacs to rule them all