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

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Message-ID: <d1d45a72-1506-4b81-a905-b9e94eb52825@suse.com>
Date: Wed, 14 May 2025 17:56:27 +0200
From: Jürgen Groß <jgross@...e.com>
To: Roger Pau Monne <roger.pau@...rix.com>, xen-devel@...ts.xenproject.org,
 linux-kernel@...r.kernel.org
Cc: jason.andryuk@....com, John <jw@...learfallout.net>,
 Stefano Stabellini <sstabellini@...nel.org>,
 Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
Subject: Re: [PATCH] xen/x86: fix initial memory balloon target

On 14.05.25 10:04, 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>

Reviewed-by: Juergen Gross <jgross@...e.com>


Juergen

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