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Subject: Re: [PATCH v4 2/5] x86/sgx: Reduce the locking range in
 sgx_sanitize_section()
To:     Jarkko Sakkinen <jarkko@kernel.org>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Sean Christopherson <seanjc@google.com>,
        Shuah Khan <shuah@kernel.org>, x86@kernel.org,
        linux-sgx@vger.kernel.org, linux-kselftest@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Jia Zhang <zhang.jia@linux.alibaba.com>
References: <20210201132653.35690-1-tianjia.zhang@linux.alibaba.com>
 <20210201132653.35690-3-tianjia.zhang@linux.alibaba.com>
 <YBnLaEz0hi/s9T8X@kernel.org>
From:   Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Message-ID: <ef2fb93a-819a-fb67-b3d0-b0aa5a7e62bf@linux.alibaba.com>
Date:   Thu, 11 Feb 2021 14:15:16 +0800
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On 2/3/21 6:00 AM, Jarkko Sakkinen wrote:
> On Mon, Feb 01, 2021 at 09:26:50PM +0800, Tianjia Zhang wrote:
>> The spin lock of sgx_epc_section only locks the page_list. The
>> EREMOVE operation and init_laundry_list is not necessary in the
>> protection range of the spin lock. This patch reduces the lock
>> range of the spin lock in the function sgx_sanitize_section()
>> and only protects the operation of the page_list.
>>
>> Suggested-by: Sean Christopherson <seanjc@google.com>
>> Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
> 
> I'm not confident that this change has any practical value.
> 
> /Jarkko
> 

As a process executed during initialization, this optimization effect 
may not be obvious. If possible, this critical area can be moved outside 
to protect the entire while loop.

Best regards,
Tianjia
>> ---
>>   arch/x86/kernel/cpu/sgx/main.c | 11 ++++-------
>>   1 file changed, 4 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
>> index c519fc5f6948..4465912174fd 100644
>> --- a/arch/x86/kernel/cpu/sgx/main.c
>> +++ b/arch/x86/kernel/cpu/sgx/main.c
>> @@ -41,20 +41,17 @@ static void sgx_sanitize_section(struct sgx_epc_section *section)
>>   		if (kthread_should_stop())
>>   			return;
>>   
>> -		/* needed for access to ->page_list: */
>> -		spin_lock(&section->lock);
>> -
>>   		page = list_first_entry(&section->init_laundry_list,
>>   					struct sgx_epc_page, list);
>>   
>>   		ret = __eremove(sgx_get_epc_virt_addr(page));
>> -		if (!ret)
>> +		if (!ret) {
>> +			spin_lock(&section->lock);
>>   			list_move(&page->list, &section->page_list);
>> -		else
>> +			spin_unlock(&section->lock);
>> +		} else
>>   			list_move_tail(&page->list, &dirty);
>>   
>> -		spin_unlock(&section->lock);
>> -
>>   		cond_resched();
>>   	}
>>   
>> -- 
>> 2.19.1.3.ge56e4f7
>>
>>