linux-kernel - Re: [PATCH v9 07/18] x86/virt/tdx: Do TDX module per-cpu initialization

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Date:   Mon, 13 Feb 2023 14:43:12 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Huang, Kai" <kai.huang@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Cc:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "Brown, Len" <len.brown@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "Gao, Chao" <chao.gao@...el.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "david@...hat.com" <david@...hat.com>,
        "bagasdotme@...il.com" <bagasdotme@...il.com>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "imammedo@...hat.com" <imammedo@...hat.com>
Subject: Re: [PATCH v9 07/18] x86/virt/tdx: Do TDX module per-cpu
 initialization

On 2/13/23 13:19, Huang, Kai wrote:
>> On 2/13/23 03:59, Kai Huang wrote:
>>> To avoid duplicated code, add a
>>> helper to call SEAMCALL on all online cpus one by one but with a skip
>>> function to check whether to skip certain cpus, and use that helper to
>>> do the per-cpu initialization.
>> ...
>>> +/*
>>> + * Call @func on all online cpus one by one but skip those cpus
>>> + * when @skip_func is valid and returns true for them.
>>> + */
>>> +static int tdx_on_each_cpu_cond(int (*func)(void *), void *func_data,
>>> +                           bool (*skip_func)(int cpu, void *),
>>> +                           void *skip_data)
>> I only see one caller of this.  Where is the duplicated code?
> The other caller is in patch 15 (x86/virt/tdx: Configure global KeyID on all packages).
> 
> I kinda mentioned this in the changelog:
> 
>         " Similar to the per-cpu module initialization, a later step to config the key for the global KeyID..."
> 
> If we don't have this helper, then we can end up with having below loop in two functions:
> 
>         for_each_online(cpu) {
>                 if (should_skip(cpu))
>                         continue;
> 
>                 // call @func on @cpu.
>         }

I don't think saving two lines of actual code is worth the opacity that
results from this abstraction.