linux-kernel - Re: [PATCH v4 2/5] x86/sgx: Reduce the locking range in sgx_sanitize

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Date:   Wed, 3 Feb 2021 00:00:08 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Shuah Khan <shuah@...nel.org>, x86@...nel.org,
        linux-sgx@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Jia Zhang <zhang.jia@...ux.alibaba.com>
Subject: Re: [PATCH v4 2/5] x86/sgx: Reduce the locking range in
 sgx_sanitize_section()

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@...gle.com>
> Signed-off-by: Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>

I'm not confident that this change has any practical value.

/Jarkko

> ---
>  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
> 
>