linux-kernel - Re: [PATCH v1 01/31] x86/resctrl: Fix allocation of cleanest CLOSID on platforms with no monitors

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Message-ID: <ZhfwAASIZsjTu5b1@e133380.arm.com>
Date: Thu, 11 Apr 2024 15:13:20 +0100
From: Dave Martin <Dave.Martin@....com>
To: Reinette Chatre <reinette.chatre@...el.com>
Cc: James Morse <james.morse@....com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, Fenghua Yu <fenghua.yu@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	H Peter Anvin <hpa@...or.com>, Babu Moger <Babu.Moger@....com>,
	shameerali.kolothum.thodi@...wei.com,
	D Scott Phillips OS <scott@...amperecomputing.com>,
	carl@...amperecomputing.com, lcherian@...vell.com,
	bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
	baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
	Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
	dfustini@...libre.com, amitsinght@...vell.com,
	David Hildenbrand <david@...hat.com>,
	Rex Nie <rex.nie@...uarmicro.com>
Subject: Re: [PATCH v1 01/31] x86/resctrl: Fix allocation of cleanest CLOSID
 on platforms with no monitors

On Mon, Apr 08, 2024 at 08:13:40PM -0700, Reinette Chatre wrote:
> Hi James,
> 
> On 3/21/2024 9:50 AM, James Morse wrote:
> > commit 6eac36bb9eb0 ("x86/resctrl: Allocate the cleanest CLOSID by
> > searching closid_num_dirty_rmid") added a Kconfig option that causes
> 
> Please see section about "Fixes" tags in section "Ordering of commit tags"
> in Documentation/process/maintainer-tip.rst

Noted for James' attention.

> > resctrl to search for the CLOSID with the fewest dirty cache lines when
> > creating a new control group. This depends on the values read from the
> > llc_occupancy counters.
> > 
> > This support missed that some platforms may not have these counters.
> > This causes a NULL pointer dereference when creating a new control
> > group as the array was not allocated by dom_data_init().
> > 
> > As this feature isn't necessary on platforms that don't have cache
> > occupancy monitors, add this to the check that occurs when a new
> > control group is allocated.
> > 
> > The existing code is not selected by any upstream platform, it makes
> > no sense to backport this patch to stable.
> > 
> > Signed-off-by: James Morse <james.morse@....com>
> > ---
> >  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > index 011e17efb1a6..1767c1affa60 100644
> > --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > @@ -149,7 +149,8 @@ static int closid_alloc(void)
> >  
> >  	lockdep_assert_held(&rdtgroup_mutex);
> >  
> > -	if (IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID)) {
> > +	if (IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID) &&
> > +	    is_llc_occupancy_enabled()) {
> >  		cleanest_closid = resctrl_find_cleanest_closid();
> >  		if (cleanest_closid < 0)
> >  			return cleanest_closid;
> 
> Patch looks good.
> 
> Thank you
> 
> Reinette
> 

Noted, thanks.

Cheers
---Dave