linux-kernel - Re: [PATCH V8 09/44] x86/pkeys: Enable PKS on cpus which support it

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Message-ID: <97fc1205-4270-1924-d3b3-19708ada648c@intel.com>
Date:   Fri, 28 Jan 2022 15:53:22 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Ira Weiny <ira.weiny@...el.com>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V8 09/44] x86/pkeys: Enable PKS on cpus which support it

On 1/28/22 15:41, Ira Weiny wrote:
> On Fri, Jan 28, 2022 at 03:18:29PM -0800, Dave Hansen wrote:
>> On 1/27/22 09:54, ira.weiny@...el.com wrote:
>>> Initially, pks_setup() initializes the per-cpu MSR with 0 to enable all
>>> access on all pkeys.
>>
>> Why not just make it restrictive to start out?  That's what we do for PKU.
> 
> This maintains compatibility with the code prior to this patch.  Ie no
> restrictions on kernel mappings.

But, compatibility with what?  At this point, there are no non-pkey-0
kernel mappings.  So, PKRS can be set to anything as long as the two low
bits are clear.