Re: [PATCH] x86/boot/e820: Re-enable fallback if e820 table is empty

[David Gow <david@davidgow.net>]

Le 15/04/2026 à 4:51 PM, Andy Shevchenko a écrit :
> On Wed, Apr 15, 2026 at 08:30:18AM +0800, David Gow wrote:
>> In commit 157266edcc56 ("x86/boot/e820: Simplify append_e820_table() and remove restriction on single-entry tables"),
> 
> Note, it's fine to wrap this line in the commit message, it's only requirement
> to tags to be "1 tag — 1 line".
> 

Thanks -- I vaguely recall checkpatch complaining about this at some 
point, though I could've been imagining it...

>> the check that the number of entries in the e820 table was removed. The
>> intention was to support single-entry maps, but by removing the check
>> entirely, we also skip the fallback (to, e.g., the BIOS 88h function).
>>
>> This means that if no E820 map is passed in from the bootloader (which is
>> the case on some bootloaders, like linld), we end up with an empty memory
>> map, and the kernel fails to boot (either by deadlocking on OOM, or by
>> failing to allocate the real mode trampoline, or similar).
>>
>> Re-instate the check in append_e820_table(), but only check nr_entries is
>> non-zero. This allows e820__memory_setup_default() to fall back to other
>> memory size sources, and doesn't affect e820__memory_setup_extended(), as
>> the latter ignores the return value from append_e820_table().
>>
>> Tested against linld, and the kernel boots again fine.
>>
>> Fixes: 157266edcc56 ("x86/boot/e820: Simplify append_e820_table() and remove restriction on single-entry tables")
> 
> ...
> 
>>   	struct boot_e820_entry *entry = entries;
>>   
>> +	/* If there aren't any entries, we'll want to fall-back to another source. */
>> +	if (!nr_entries)
>> +		return -1;
> 
> Can we return -ENODATA or -ENOENT here?
> 

Sounds like a good idea. The previous code (like this) used -1 for both 
"there are no entires" and "there are entries which look bogus". Maybe 
we should replace the latter with -EINVAL, too.

-- David