linux-kernel - Re: [PATCH V8 07/44] x86/pkeys: Add PKS CPU feature bit

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Message-ID: <20220204192128.GA785175@iweiny-DESK2.sc.intel.com>
Date:   Fri, 4 Feb 2022 11:21:28 -0800
From:   Ira Weiny <ira.weiny@...el.com>
To:     Dave Hansen <dave.hansen@...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 07/44] x86/pkeys: Add PKS CPU feature bit

On Fri, Jan 28, 2022 at 03:05:36PM -0800, Dave Hansen wrote:
> On 1/27/22 09:54, ira.weiny@...el.com wrote:
> > From: Ira Weiny <ira.weiny@...el.com>
> > 
> > Protection Keys for Supervisor pages (PKS) enables fast, hardware thread
> > specific, manipulation of permission restrictions on supervisor page
> 
> Nit: should be "hardware-thread-specific".
> 
> > mappings.  It uses the same mechanism of Protection Keys as those on
> > User mappings but applies that mechanism to supervisor mappings using a
> > supervisor specific MSR.
> 
> "supervisor-specific"
> 
> 	Memory Protection Keys (pkeys) provides a mechanism for
> 	enforcing page-based protections, but without requiring
> 	modification of the page tables when an application changes
> 	protection domains.
> 
> 	The kernel currently supports the pkeys for userspace (PKU)
> 	architecture.  That architecture has been extended to
> 	additionally support supervisor mappings.  The supervisor
> 	support is referred to as PKS.
> 
> I probably wouldn't mention the MSR unless you want to say:
> 
> 	The main difference between PKU and PKS is that PKS does not
> 	introduce any new instructions to write to its register.  The
> 	register is exposed as a normal MSR and is accessed with the
> 	normal MSR instructions.
> 
> 
> > The CPU indicates support for PKS in bit 31 of the ECX register after a
> > cpuid instruction.
> 
> I'd just remove this sentence.  We don't need to rehash each tiny morsel
> of the architecture in a commit message.

All done.  Thanks for the verbiage.
Ira