Re: [RFC PATCH v2 1/1] x86/pkeys: update PKRU to enable pkey 0 before XSAVE

[jeffxu]

From: Jeff Xu <jeffxu@xxxxxxxxxxxx>

>The semantics you've implemented for sigaltstacks are not the only possible 
>ones. In principle, a signal handler with its own stack might want to have 
>its own key(s) enabled. In a way a Linux signal handler is a mini-thread 
>created on the fly, with its own stack and its own attributes. Some thought 
>& analysis should go into which way to go here, and the best path should be 
>chosen. Fixing the SIGSEGV you observed should be a happy side effect of 
>other worthwile improvements.
>
This is exactly right. we wants to use altstack with its own pkey. The pkey
won't be writeable during thread's normal operation, only by signaling
handling itself.

Thanks
-Jeff

>Thanks,
>
>	Ingo
>