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SubjectRe: [PATCH v4 4/4] sparc64: Add support for ADI (Application Data Integrity)
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On 01/16/2017 09:39 PM, David Miller wrote:
> 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.

Hi David,

"rd %%asr14, %0" should work but does not due to bugs in assembler -
<https://sourceware.org/ml/binutils/2016-03/msg00302.html>, and
<https://sourceware.org/ml/binutils/2016-03/msg00303.html>. These bugs
were fixed in binutils 2.27 but older assemblers will cause kernel build
to fail. Using byte coded equivalent is the safest option.

>
>> + ".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?

%pmcdper is not an asr, rather a privileged register (pr23).

Thanks,
Khalid

>
>> 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.
> --
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