Re: [PATCH v4 4/4] sparc64: Add support for ADI (Application Data Integrity)

From: David Miller <davem@davemloft.net>
To: khalid.aziz@oracle.com
Cc: corbet@lwn.net, viro@zeniv.linux.org.uk,
	nitin.m.gupta@oracle.com, mike.kravetz@oracle.com,
	akpm@linux-foundation.org, mingo@kernel.org,
	kirill.shutemov@linux.intel.com, adam.buchbinder@gmail.com,
	hughd@google.com, minchan@kernel.org, keescook@chromium.org,
	chris.hyser@oracle.com, atish.patra@oracle.com,
	cmetcalf@mellanox.com, atomlin@redhat.com, jslaby@suse.cz,
	joe@perches.com, paul.gortmaker@windriver.com, mhocko@suse.com,
	lstoakes@gmail.com, jack@suse.cz, dave.hansen@linux.intel.com,
	vbabka@suse.cz, dan.j.williams@intel.com, iamjoonsoo.kim@lge.com,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	sparclinux@vger.kernel.org, linux-mm@kvack.org,
	khalid@gonehiking.org
Subject: Re: [PATCH v4 4/4] sparc64: Add support for ADI (Application Data Integrity)
Date: Mon, 16 Jan 2017 23:39:24 -0500 (EST)	[thread overview]
Message-ID: <20170116.233924.374841184595409216.davem@davemloft.net> (raw)
In-Reply-To: <0c08eb00e5a9735d7d0bcbeaadeacaa761011aab.1483999591.git.khalid.aziz@oracle.com>

From: Khalid Aziz <khalid.aziz@oracle.com>
Date: Wed, 11 Jan 2017 09:12:54 -0700

> +		__asm__ __volatile__(
> +			".word 0xa1438000\n\t"	/* rd  %mcdper, %l0 */

Just use "rd %%asr14, %0" this way you don't have to play all of these
fixed register games which kill the code generated by gcc.  If you
forcefully clobber a windowed register like %l0 it means the function
being emitted can never be a leaf function, tail calls are no longer
allowed, etc.

> +			".word 0x9d800011\n\t"	/* wr  %g0, %l1, %mcdper */

Likewise use "wr %%g0, %0, %%asr14"

> +		".word 0xaf900001\n\t"	/* wrpr  %g0, %g1, %pmcdper */

Hmmm, which %asr encodes %pmcdper?

> diff --git a/arch/sparc/kernel/mdesc.c b/arch/sparc/kernel/mdesc.c
> index 8a6982d..68b03bf 100644
> --- a/arch/sparc/kernel/mdesc.c
> +++ b/arch/sparc/kernel/mdesc.c
> @@ -20,6 +20,7 @@
>  #include <asm/uaccess.h>
>  #include <asm/oplib.h>
>  #include <asm/smp.h>
> +#include <asm/adi.h>
>  
>  /* Unlike the OBP device tree, the machine description is a full-on
>   * DAG.  An arbitrary number of ARCs are possible from one
> @@ -1104,5 +1105,8 @@ void __init sun4v_mdesc_init(void)
>  
>  	cur_mdesc = hp;
>  
> +#ifdef CONFIG_SPARC64

mdesc.c is only built on sparc64, this ifdef is superfluous.

> +/* Update the state of MCDPER register in current task's mm context before
> + * dup so the dup'd task will inherit flags in this register correctly.
> + * Current task may have updated flags since it started running.
> + */
> +int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
> +{
> +	if (adi_capable() && src->mm) {
> +		register unsigned long tmp_mcdper;
> +
> +		__asm__ __volatile__(
> +			".word 0x83438000\n\t"	/* rd %mcdper, %g1 */
> +			"mov %%g1, %0\n\t"
> +			: "=r" (tmp_mcdper)
> +			:
> +			: "g1");
> +		src->mm->context.mcdper = tmp_mcdper;

I don't like the idea of duplicating 'mm' state using the task struct
copy.  Why do not the MM handling interfaces handle this properly?

Maybe it means you've abstracted the ADI register handling in the
wrong place.  Maybe it's a thread property which is "pushed" from
the MM context.