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

[Khalid Aziz]

On 08/30/2017 06:09 PM, David Miller wrote:
> From: Khalid Aziz <khalid.aziz@xxxxxxxxxx>
> 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