linux-kernel - Re: [PATCH] xen/x86: fix initial memory balloon target

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Message-ID: <aEBWmAoDSaNpsrvQ@mail-itl>
Date: Wed, 4 Jun 2025 16:22:16 +0200
From: Marek Marczykowski-Górecki <marmarek@...isiblethingslab.com>
To: Roger Pau Monne <roger.pau@...rix.com>
Cc: Juergen Gross <jgross@...e.com>, xen-devel@...ts.xenproject.org,
	linux-kernel@...r.kernel.org, jason.andryuk@....com,
	John <jw@...learfallout.net>,
	Stefano Stabellini <sstabellini@...nel.org>,
	Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
	stable@...r.kernel.org
Subject: Re: [PATCH] xen/x86: fix initial memory balloon target

On Thu, May 15, 2025 at 11:01:24AM +0200, Marek Marczykowski-Górecki wrote:
> On Wed, May 14, 2025 at 10:04:26AM +0200, Roger Pau Monne wrote:
> > When adding extra memory regions as ballooned pages also adjust the balloon
> > target, otherwise when the balloon driver is started it will populate
> > memory to match the target value and consume all the extra memory regions
> > added.
> > 
> > This made the usage of the Xen `dom0_mem=,max:` command line parameter for
> > dom0 not work as expected, as the target won't be adjusted and when the
> > balloon is started it will populate memory straight to the 'max:' value.
> > It would equally affect domUs that have memory != maxmem.
> > 
> > Kernels built with CONFIG_XEN_UNPOPULATED_ALLOC are not affected, because
> > the extra memory regions are consumed by the unpopulated allocation driver,
> > and then balloon_add_regions() becomes a no-op.
> > 
> > Reported-by: John <jw@...learfallout.net>
> > Fixes: 87af633689ce ('x86/xen: fix balloon target initialization for PVH dom0')
> > Signed-off-by: Roger Pau Monné <roger.pau@...rix.com>
> 
> Tested-by: Marek Marczykowski-Górecki <marmarek@...isiblethingslab.com>

I think this wants Cc: stable, since the commit named in Fixes: got
backported too. Or is the Fixes tag enough?

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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