linux-kernel - Re: [PATCH V8 41/44] kmap: Ensure kmap works for devmap pages

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Message-ID: <Yh55EQ4BTN/VNpAI@iweiny-desk3>
Date:   Tue, 1 Mar 2022 11:50:41 -0800
From:   Ira Weiny <ira.weiny@...el.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V8 41/44] kmap: Ensure kmap works for devmap pages

On Tue, Mar 01, 2022 at 11:45:41AM -0800, Ira Weiny wrote:
> On Fri, Feb 04, 2022 at 01:07:10PM -0800, Dan Williams wrote:
> > On Thu, Jan 27, 2022 at 9:55 AM <ira.weiny@...el.com> wrote:
> > >
> > > From: Ira Weiny <ira.weiny@...el.com>
> > >
> 
> > 
> > > Co-opt the kmap_{local_page,atomic}() to mediate access to PKS protected
> > > pages via the devmap facility.  kmap_{local_page,atomic}() are both
> > > thread local mappings so they work well with the thread specific
> > > protections available.
> > >
> > > kmap(), on the other hand, allows for global mappings to be established,
> > > Which is incompatible with the underlying PKS facility.
> > 
> > Why is kmap incompatible with PKS? I know why, but this is a claim
> > without evidence. If you documented that in a previous patch, there's
> > no harm and copying and pasting into this one. A future git log user
> > will thank you for not making them go to lore to try to find the one
> > patch with the  details.
> 
> Good point.
> 

FWIW, I just noticed the previous paragraph mentioned the PKS protections were
thread local.  I'll still reiterate and clarify here.

Ira