linux-kernel - Re: [PATCH v7 9/9] sparc64: Add support for ADI (Application Data Integrity)

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Message-ID: <3ff76988-43f2-85e4-eaf4-cc0d10b420a3@oracle.com>
Date:   Thu, 31 Aug 2017 10:38:30 -0600
From:   Khalid Aziz <khalid.aziz@...cle.com>
To:     David Miller <davem@...emloft.net>
Cc:     anthony.yznaga@...cle.com, dave.hansen@...ux.intel.com,
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Subject: Re: [PATCH v7 9/9] sparc64: Add support for ADI (Application Data
 Integrity)

On 08/30/2017 06:09 PM, David Miller wrote:
> From: Khalid Aziz <khalid.aziz@...cle.com>
> Date: Wed, 30 Aug 2017 17:23:37 -0600
> 
>> That is an interesting idea. This would enable TSTATE_MCDE on all
>> threads of a process as soon as one thread enables it. If we consider
>> the case where the parent creates a shared memory area and spawns a
>> bunch of threads. These threads access the shared memory without ADI
>> enabled. Now one of the threads decides to enable ADI on the shared
>> memory. As soon as it does that, we enable TSTATE_MCDE across all
>> threads and since threads are all using the same TTE for the shared
>> memory, every thread becomes subject to ADI verification. If one of
>> the other threads was in the middle of accessing the shared memory, it
>> will get a sigsegv. If we did not enable TSTATE_MCDE across all
>> threads, it could have continued execution without fault. In other
>> words, updating TSTATE_MCDE across all threads will eliminate the
>> option of running some threads with ADI enabled and some not while
>> accessing the same shared memory. This could be necessary at least for
>> short periods of time before threads can communicate with each other
>> and all switch to accessing shared memory with ADI enabled using same
>> tag. Does that sound like a valid use case or am I off in the weeds
>> here?
> 
> A threaded application needs to synchronize and properly orchestrate
> access to shared memory.
> 
> When a change is made to a mappping, in this case setting ADI
> attributes, it's being done for the address space not the thread.
> 
> And the address space is shared amongst threads.
> 
> Therefore ADI is not really a per-thread property but rather
> a per-address-space property.
> 

That does make sense.

Thanks,
Khalid