From: Ram Pai <linuxram@us.ibm.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Linux-MM <linux-mm@kvack.org>,
Dave Hansen <dave.hansen@intel.com>
Subject: Re: pkeys on POWER: Default AMR, UAMOR values
Date: Fri, 18 May 2018 17:52:19 -0700 [thread overview]
Message-ID: <20180519005219.GI5479@ram.oc3035372033.ibm.com> (raw)
In-Reply-To: <27e01118-be5c-5f90-78b2-56bb69d2ab95@redhat.com>
On Fri, May 18, 2018 at 11:13:30PM +0200, Florian Weimer wrote:
> On 05/18/2018 09:39 PM, Andy Lutomirski wrote:
> >The difference is that x86 starts out with deny-all instead of allow-all.
Ah!. this explains the discrepency. But still does not explain one
thing.. see below.
> >The POWER semantics make it very hard for a multithreaded program to
> >meaningfully use protection keys to prevent accidental access to important
> >memory.
>
> And you can change access rights for unallocated keys (unallocated
> at thread start time, allocated later) on x86. I have extended the
> misc/tst-pkeys test to verify that, and it passes on x86, but not on
> POWER, where the access rights are stuck.
This is something I do not understand. How can a thread change permissions
on a key, that is not even allocated in the first place. Do you consider a key
allocated in some other thread's context, as allocated in this threads
context? If not, does that mean -- On x86, you can activate a key just
by changing its permission?
RP
next prev parent reply other threads:[~2018-05-19 0:52 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-18 13:17 pkeys on POWER: Default AMR, UAMOR values Florian Weimer
2018-05-18 14:35 ` Andy Lutomirski
2018-05-18 17:44 ` Ram Pai
2018-05-18 19:39 ` Andy Lutomirski
2018-05-18 21:13 ` Florian Weimer
2018-05-19 0:52 ` Ram Pai [this message]
2018-05-19 5:15 ` Florian Weimer
2018-05-18 21:09 ` Florian Weimer
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