Message-ID: <af6034c3-98a3-239b-2c79-ff878f5d9673@intel.com>
Date:   Mon, 13 Feb 2023 14:43:12 -0800
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.6.1
Subject: Re: [PATCH v9 07/18] x86/virt/tdx: Do TDX module per-cpu
 initialization
Content-Language: en-US
To:     "Huang, Kai" <kai.huang@intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>
Cc:     "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "peterz@infradead.org" <peterz@infradead.org>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "Christopherson,, Sean" <seanjc@google.com>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "Williams, Dan J" <dan.j.williams@intel.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@intel.com>,
        "kirill.shutemov@linux.intel.com" <kirill.shutemov@linux.intel.com>,
        "Huang, Ying" <ying.huang@intel.com>,
        "Chatre, Reinette" <reinette.chatre@intel.com>,
        "Brown, Len" <len.brown@intel.com>,
        "Luck, Tony" <tony.luck@intel.com>,
        "ak@linux.intel.com" <ak@linux.intel.com>,
        "Yamahata, Isaku" <isaku.yamahata@intel.com>,
        "Gao, Chao" <chao.gao@intel.com>,
        "sathyanarayanan.kuppuswamy@linux.intel.com" 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        "david@redhat.com" <david@redhat.com>,
        "bagasdotme@gmail.com" <bagasdotme@gmail.com>,
        "Shahar, Sagi" <sagis@google.com>,
        "imammedo@redhat.com" <imammedo@redhat.com>
References: <cover.1676286526.git.kai.huang@intel.com>
 <557c526a1190903d11d67c4e2c76e01f67f6eb15.1676286526.git.kai.huang@intel.com>
 <86a8fe2f-566a-d0b9-7a22-9b41c91796f8@intel.com>
 <BL1PR11MB59789A024CFA9E9DE715C2F1F7DD9@BL1PR11MB5978.namprd11.prod.outlook.com>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <BL1PR11MB59789A024CFA9E9DE715C2F1F7DD9@BL1PR11MB5978.namprd11.prod.outlook.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

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.