[PATCH v2] x86/sgx: Remove redundant if conditions in sgx_encl_create

[PATCH v2] x86/sgx: Remove redundant if conditions in sgx_encl_create

[Tianjia Zhang]

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@linux.alibaba.com>
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.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"))
+		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

Re: [PATCH v2] x86/sgx: Remove redundant if conditions in sgx_encl_create

[Sean Christopherson]

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@linux.alibaba.com>
> Suggested-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.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"))

> +		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
> 

Re: [PATCH v2] x86/sgx: Remove redundant if conditions in sgx_encl_create

[Jarkko Sakkinen]

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@linux.alibaba.com>
> > Suggested-by: Sean Christopherson <seanjc@google.com>
> > Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.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
> > 
> 

Re: [PATCH v2] x86/sgx: Remove redundant if conditions in sgx_encl_create

[Tianjia Zhang]

On 1/21/21 1:47 AM, 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@linux.alibaba.com>
>> Suggested-by: Sean Christopherson <seanjc@google.com>
>> Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.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"))
> 

Thanks for your suggestion, I have resubmitted a set of patches.

Best regards,
Tianjia