Re: [PATCH v3] x86/e820: Fix handling of subpage regions when calculating nosave ranges

* Ingo Molnar mingo@kernel.org wrote:

• Myrrh Periwinkle myrrhperiwinkle@qtmlabs.xyz wrote:

...

The current implementation of e820__register_nosave_regions suffers from multiple serious issues:

• The end of last region is tracked by PFN, causing it to find holes that aren't there if two consecutive subpage regions are present
• The nosave PFN ranges derived from holes are rounded out (instead of rounded in) which makes it inconsistent with how explicitly reserved regions are handled

Fix this by:

• Treating reserved regions as if they were holes, to ensure consistent handling (rounding out nosave PFN ranges is more correct as the kernel does not use partial pages)
• Tracking the end of the last RAM region by address instead of pages to detect holes more precisely

Cc: stable@vger.kernel.org Fixes: e5540f875404 ("x86/boot/e820: Consolidate 'struct e820_entry *entry' local variable names")

So why is this SHA1 indicated as the root cause? AFAICS that commit does nothing but cleanups, so it cannot cause such regressions.

BTW.:

A) "It was the first random commit that seemed related, sry" B) "It's a 15 years old bug, but I wanted to indicate a fresh, 8-year old bug to get this into -stable. Busted!"

... are perfectly fine answers in my book. :-)

I'm glad about the fixes, I'm just curious how the Fixes tag came about.

Thanks,

Ingo