linux-kernel - Re: [PATCH 2/2] x86/xen: fix memblock

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Message-ID: <ZqIIgc9xj6wmDJtE@macbook>
Date: Thu, 25 Jul 2024 10:10:41 +0200
From: Roger Pau Monné <roger.pau@...rix.com>
To: Jürgen Groß <jgross@...e.com>
Cc: xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	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>
Subject: Re: [PATCH 2/2] x86/xen: fix memblock_reserve() usage on PVH

On Thu, Jul 25, 2024 at 10:01:17AM +0200, Jürgen Groß wrote:
> On 25.07.24 09:31, Roger Pau Monne wrote:
> > The current usage of memblock_reserve() in init_pvh_bootparams() is done before
> > the .bss is zeroed, and that used to be fine when
> > memblock_reserved_init_regions implicitly ended up in the .meminit.data
> > section.  However after commit 73db3abdca58c memblock_reserved_init_regions
> > ends up in the .bss section, thus breaking it's usage before the .bss is
> > cleared.
> > 
> > Move and rename the call to xen_reserve_extra_memory() so it's done in the
> > x86_init.oem.arch_setup hook, which gets executed after the .bss has been
> > zeroed, but before calling e820__memory_setup().
> > 
> > Fixes: 38620fc4e893 ('x86/xen: attempt to inflate the memory balloon on PVH')
> > Signed-off-by: Roger Pau Monné <roger.pau@...rix.com>
> > ---
> > While the commit that introduced the user-noticeable regression is
> > 73db3abdca58c, I think 38620fc4e893 should have been more careful to not
> > initialize the memblock ranges ahead of the .bss zeroing.
> 
> Reviewed-by: Juergen Gross <jgross@...e.com>
> 
> I'd prefer using 73db3abdca58c for the fixes tag. Otherwise you'd need to
> add this patch to the stable branches, too, which is technically not really
> needed.
> 
> Additionally I'd like to drop the Fixes: tag from the prereq patch, as this
> one doesn't really fix anything.
> 
> I can do both while committing.

I was unsure myself (as noted in the post-commit notes) about which
"Fixes:" tag to use.

Is there anyway that it can be noted that this commit depends on the
previous change also being present?  For backport reasons, if anyone
ends up backporting 73db3abdca58c it would also need to pick the two
patches here.

Thanks, Roger.