Subject: Re: [PATCH v2] sparc64: Add support for Application Data Integrity
 (ADI)
To: Rob Gardner <rob.gardner@oracle.com>, David Miller <davem@davemloft.net>
References: <1456951177-23579-1-git-send-email-khalid.aziz@oracle.com>
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        linux-arch@vger.kernel.org, linux-api@vger.kernel.org
From: Khalid Aziz <khalid.aziz@oracle.com>
Organization: Oracle Corp
Message-ID: <56DDC776.3040003@oracle.com>
Date: Mon, 7 Mar 2016 11:24:54 -0700
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On 03/07/2016 11:09 AM, Rob Gardner wrote:
> On 03/07/2016 10:04 AM, Khalid Aziz wrote:
>> On 03/07/2016 09:56 AM, David Miller wrote:
>>> From: Khalid Aziz <khalid.aziz@oracle.com>
>>> Date: Mon, 7 Mar 2016 08:07:53 -0700
>>>
>>>> PR_GET_SPARC_ADICAPS
>>>
>>> Put this into a new ELF auxiliary vector entry via ARCH_DLINFO.
>>>
>>> So now all that's left is supposedly the TAG stuff, please explain
>>> that to me so I can direct you to the correct existing interface to
>>> provide that as well.
>>>
>>> Really, try to avoid prtctl, it's poorly typed and almost worse than
>>> ioctl().
>>>
>>
>> The two remaining operations I am looking at are:
>>
>> 1. Is PSTATE.mcde bit set for the process? PR_SET_SPARC_ADI provides
>> this in its return value in the patch I sent.
>>
>> 2. Is TTE.mcd set for a given virtual address? PR_GET_SPARC_ADI_STATUS
>> provides this function in the patch I sent.
>>
>> Setting and clearing version tags can be done entirely from userspace:
>>
>>         while (addr < end) {
>>                 asm volatile(
>>                         "stxa %1, [%0]ASI_MCD_PRIMARY\n\t"
>>                         :
>>                         : "r" (addr), "r" (version));
>>                 addr += adicap.blksz;
>>         }
>> so I do not have to add any kernel code for tags.
>>
>
> What about clearing the tags when the user is done with the memory? You
> can't count on the user to do that, so doesn't the kernel have to do it
> someplace?
>

Tags can be cleared by user by setting tag to 0. Tags are automatically 
cleared by the hardware when the mapping for a virtual address is 
removed from TSB (which is why swappable pages are a problem), so kernel 
does not have to do it as part of clean up.

Thanks,
Khalid