linux-kernel - Re: [PATCH] x86/sgx: Remove redundant if conditions in sgx_encl

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Message-ID: <YAdBGO00lEmAHR1g@google.com>
Date:   Tue, 19 Jan 2021 12:29:12 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
Cc:     Jarkko Sakkinen <jarkko@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, haitao.huang@...el.com,
        Kai Huang <kai.huang@...el.com>, x86@...nel.org,
        linux-sgx@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
        Jia Zhang <zhang.jia@...ux.alibaba.com>
Subject: Re: [PATCH] x86/sgx: Remove redundant if conditions in
 sgx_encl_create

On Mon, Jan 18, 2021, Tianjia Zhang wrote:
> In this scenario, there is no case where va_page is NULL, and
> the error has been checked. The if condition statement here is
> redundant, so remove the condition detection.
> 
> Reported-by: Jia Zhang <zhang.jia@...ux.alibaba.com>
> Signed-off-by: Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
> ---
>  arch/x86/kernel/cpu/sgx/ioctl.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
> index 90a5caf76939..f45957c05f69 100644
> --- a/arch/x86/kernel/cpu/sgx/ioctl.c
> +++ b/arch/x86/kernel/cpu/sgx/ioctl.c
> @@ -66,9 +66,8 @@ static int sgx_encl_create(struct sgx_encl *encl, struct sgx_secs *secs)
>  	va_page = sgx_encl_grow(encl);
>  	if (IS_ERR(va_page))
>  		return PTR_ERR(va_page);
> -	else if (va_page)
> -		list_add(&va_page->list, &encl->va_pages);
> -	/* else the tail page of the VA page list had free slots. */
> +
> +	list_add(&va_page->list, &encl->va_pages);

Maybe add a WARN_ONCE to document/enforce the behavior?

	va_page = sgx_encl_grow(encl);
	if (IS_ERR(va_page))
		return PTR_ERR(va_page);

	if (WARN_ONCE(!va_page, "clever comment goes here))
		return -EIO;

	list_add(&va_page->list, &encl->va_pages);

>  
>  	/* The extra page goes to SECS. */
>  	encl_size = secs->size + PAGE_SIZE;
> -- 
> 2.19.1.3.ge56e4f7
>