linux-kernel - Re: [PATCH 02/14] arm64: Call ARCH_WORKAROUND

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Date:   Thu, 24 May 2018 13:10:24 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Mark Rutland <mark.rutland@....com>,
        Julien Grall <julien.grall@....com>
Cc:     Kees Cook <keescook@...omium.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 02/14] arm64: Call ARCH_WORKAROUND_2 on transitions
 between EL0 and EL1

On 24/05/18 11:52, Mark Rutland wrote:
> On Wed, May 23, 2018 at 10:23:20AM +0100, Julien Grall wrote:
>> Hi Marc,
>>
>> On 05/22/2018 04:06 PM, Marc Zyngier wrote:
>>> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
>>> index ec2ee720e33e..f33e6aed3037 100644
>>> --- a/arch/arm64/kernel/entry.S
>>> +++ b/arch/arm64/kernel/entry.S
>>> @@ -18,6 +18,7 @@
>>>     * along with this program.  If not, see <http://www.gnu.org/licenses/>.
>>>     */
>>> +#include <linux/arm-smccc.h>
>>>    #include <linux/init.h>
>>>    #include <linux/linkage.h>
>>> @@ -137,6 +138,18 @@ alternative_else_nop_endif
>>>    	add	\dst, \dst, #(\sym - .entry.tramp.text)
>>>    	.endm
>>> +	// This macro corrupts x0-x3. It is the caller's duty
>>> +	// to save/restore them if required.
>>
>> NIT: Shouldn't you use /* ... */ for multi-line comments?
> 
> There's no requirement to do so, and IIRC even Torvalds prefers '//'
> comments for multi-line things these days.

Also, this is an assembly code, not C; '//' is the actual A64 assembler 
comment syntax so is arguably more appropriate here in spite of being 
moot thanks to preprocessing.

Robin.