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Date: Tue, 12 Mar 2024 15:06:32 -0500
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From: "Moger, Babu" <babu.moger@amd.com>
Subject: Re: [PATCH v5 1/2] x86/resctrl: Pass domain to target CPU
Reply-To: babu.moger@amd.com
To: Tony Luck <tony.luck@intel.com>,
 "Chatre, Reinette" <reinette.chatre@intel.com>,
 Borislav Petkov <bp@alien8.de>, James Morse <james.morse@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, x86@kernel.org,
 linux-kernel@vger.kernel.org, "Yu, Fenghua" <fenghua.yu@intel.com>,
 Ingo Molnar <mingo@redhat.com>, H Peter Anvin <hpa@zytor.com>,
 shameerali.kolothum.thodi@huawei.com,
 D Scott Phillips OS <scott@os.amperecomputing.com>,
 carl@os.amperecomputing.com, lcherian@marvell.com,
 bobo.shaobowang@huawei.com, tan.shaopeng@fujitsu.com,
 baolin.wang@linux.alibaba.com, Jamie Iles <quic_jiles@quicinc.com>,
 Xin Hao <xhao@linux.alibaba.com>, peternewman@google.com,
 dfustini@baylibre.com, amitsinght@marvell.com,
 David Hildenbrand <david@redhat.com>,
 Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
References: <ZdZPht8hY4J9uIOz@agluck-desk3>
 <20240308213846.77075-1-tony.luck@intel.com>
 <20240308213846.77075-2-tony.luck@intel.com>
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On 3/8/24 15:38, Tony Luck wrote:
> reset_all_ctrls() and resctrl_arch_update_domains() use on_each_cpu_mask()
> to call rdt_ctrl_update() on potentially one CPU from each domain.
> 
> But this means rdt_ctrl_update() needs to figure out which domain to
> apply changes to. Doing so requires a search of all domains in a resource,
> which can only be done safely if cpus_lock is held. Both callers do hold
> this lock, but there isn't a way for a function called on another CPU
> via IPI to verify this.
> 
> Commit c0d848fcb09d ("x86/resctrl: Remove lockdep annotation that triggers
> false positive") removed the incorrect assertions.
> 
> Add the target domain to the msr_param structure and
> call rdt_ctrl_update() for each domain separately using
> smp_call_function_single(). This means that rdt_ctrl_update() doesn't
> need to search for the domain and get_domain_from_cpu() can safely assert
> that the cpus_lock is held since the remaining callers do not use IPI.
> 
> Signed-off-by: Tony Luck <tony.luck@intel.com>
> Tested-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
> Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
> Reviewed-by: James Morse <james.morse@arm.com>

Reviewed-by: Babu Moger <babu.moger@amd.com>