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Date: Sun, 6 Apr 2025 20:36:47 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Myrrh Periwinkle <myrrhperiwinkle@qtmlabs.xyz>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
	Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
	"H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org,
	stable@vger.kernel.org, Roberto Ricci <io@r-ricci.it>
Subject: Re: [PATCH v3] x86/e820: Fix handling of subpage regions when
 calculating nosave ranges
Message-ID: <Z_LJv9gATY6nk4Yu@gmail.com>
References: <20250406-fix-e820-nosave-v3-1-f3787bc1ee1d@qtmlabs.xyz>
 <Z_LGqgUhDrTmzj5r@gmail.com>
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In-Reply-To: <Z_LGqgUhDrTmzj5r@gmail.com>


* 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