linux-kernel - Re: [PATCH v2] x86/sgx: Remove redundant if conditions in sgx_encl

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Date:   Thu, 21 Jan 2021 02:30:49 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-sgx@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jia Zhang <zhang.jia@...ux.alibaba.com>
Subject: Re: [PATCH v2] x86/sgx: Remove redundant if conditions in
 sgx_encl_create

On Wed, Jan 20, 2021 at 09:47:53AM -0800, Sean Christopherson wrote:
> On Wed, Jan 20, 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>
> > Suggested-by: Sean Christopherson <seanjc@...gle.com>
> > Signed-off-by: Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
> > ---
> >  arch/x86/kernel/cpu/sgx/ioctl.c | 9 ++++++---
> >  1 file changed, 6 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
> > index 1c6ecf9fbeff..efad2fb61c76 100644
> > --- a/arch/x86/kernel/cpu/sgx/ioctl.c
> > +++ b/arch/x86/kernel/cpu/sgx/ioctl.c
> > @@ -66,9 +66,12 @@ 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. */
> > +
> > +	if (WARN_ONCE(!va_page,
> > +		      "the tail page of the VA page list had free slots\n"))
> 
> IMO it's worth trimming down the message to keep this on a single line.  The
> newline isn't necessary, and this code expects a completely empty list, e.g. it
> can be reworded to something like:
> 
> 	if (WARN_ONCE(!va_page, "non-empty VA page list before ECREATE"))

Agreed. If I recall correctly, these days you can have at least 100
characters per line (if not more, cannot recall the exact number).

/Jarkko

> 
> > +		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
> > 
>