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

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Message-ID: <Z_LGqgUhDrTmzj5r@gmail.com>
Date: Sun, 6 Apr 2025 20:23:38 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Myrrh Periwinkle <myrrhperiwinkle@...labs.xyz>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org, Roberto Ricci <io@...icci.it>
Subject: Re: [PATCH v3] x86/e820: Fix handling of subpage regions when
 calculating nosave ranges


* Myrrh Periwinkle <myrrhperiwinkle@...labs.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@...r.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.

Thanks,

	Ingo