linux-kernel - Re: [PATCH] Partial revert "x86/xen: fix balloon target initialization for PVH dom0"

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Message-ID: <aXHej39h5cAs5-UL@Mac.lan>
Date: Thu, 22 Jan 2026 09:23:43 +0100
From: Roger Pau Monné <roger.pau@...rix.com>
To: Jan Beulich <jbeulich@...e.com>
Cc: xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
	James Dingwall <james@...gwall.me.uk>,
	Juergen Gross <jgross@...e.com>,
	Stefano Stabellini <sstabellini@...nel.org>,
	Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
	Jason Andryuk <jason.andryuk@....com>
Subject: Re: [PATCH] Partial revert "x86/xen: fix balloon target
 initialization for PVH dom0"

On Thu, Jan 22, 2026 at 08:17:22AM +0100, Jan Beulich wrote:
> On 21.01.2026 18:49, Roger Pau Monné wrote:
> > --- a/drivers/xen/balloon.c
> > +++ b/drivers/xen/balloon.c
> > @@ -724,7 +724,8 @@ static int __init balloon_add_regions(void)
> >  static int __init balloon_init(void)
> >  {
> >  	struct task_struct *task;
> > -	unsigned long current_pages;
> > +	unsigned long current_pages = 0;
> 
> With this, ...
> 
> > @@ -732,8 +733,13 @@ static int __init balloon_init(void)
> >  
> >  	pr_info("Initialising balloon driver\n");
> >  
> > -	current_pages = xen_pv_domain() ? min(xen_start_info->nr_pages, max_pfn)
> > -	                                : get_num_physpages();
> > +	if (xen_initial_domain())
> > +		current_pages = HYPERVISOR_memory_op(XENMEM_current_reservation,
> > +		                                     &domid);
> > +	if (current_pages <= 0)
> 
> ... why <= ? Gives the impression you may mean to cover HYPERVISOR_memory_op()
> returning an error, yet that'll require a signed long variable then.

Oh, indeed, current_pages should be signed long.  This was an untested
mash-up of a slightly different patch, where I didn't realize that
current_pages was unsigned.

Thanks, Roger.