linux-kernel - Re: [PATCH v5 02/24] x86/resctrl: Access per-rmid structures by index

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Date:   Wed, 9 Aug 2023 15:32:42 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     James Morse <james.morse@....com>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>
CC:     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>,
        <xingxin.hx@...nanolis.org>, <baolin.wang@...ux.alibaba.com>,
        Jamie Iles <quic_jiles@...cinc.com>,
        Xin Hao <xhao@...ux.alibaba.com>, <peternewman@...gle.com>,
        <dfustini@...libre.com>
Subject: Re: [PATCH v5 02/24] x86/resctrl: Access per-rmid structures by index

Hi James,

On 7/28/2023 9:42 AM, James Morse wrote:


> @@ -600,7 +600,7 @@ static void clear_closid_rmid(int cpu)
>  	state->default_rmid = 0;
>  	state->cur_closid = 0;
>  	state->cur_rmid = 0;
> -	wrmsr(MSR_IA32_PQR_ASSOC, 0, 0);
> +	wrmsr(MSR_IA32_PQR_ASSOC, 0, RESCTRL_RESERVED_CLOSID);
>  }

Can the remaining "0" be replaced with RESCTRL_RESERVED_RMID?


...

> @@ -377,14 +399,17 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
>  
>  void free_rmid(u32 closid, u32 rmid)
>  {
> +	u32 idx = resctrl_arch_rmid_idx_encode(closid, rmid);
>  	struct rmid_entry *entry;
>  
> -	if (!rmid)
> -		return;
> -
>  	lockdep_assert_held(&rdtgroup_mutex);
>  
> -	entry = __rmid_entry(closid, rmid);
> +	/* do not allow the default rmid to be free'd */
> +	if (idx == resctrl_arch_rmid_idx_encode(RESCTRL_RESERVED_CLOSID,
> +						RESCTRL_RESERVED_RMID))
> +		return;
> +

Why is this encoding necessary? Can the provided function parameters
not be tested directly against RESCTRL_RESERVED_CLOSID and
RESCTRL_RESERVED_RMID ?

> +	entry = __rmid_entry(idx);
>  
>  	if (is_llc_occupancy_enabled())
>  		add_rmid_to_limbo(entry);

Reinette