lkml.org 
[lkml]   [2018]   [Jul]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCHv5 10/19] x86/mm: Implement page_keyid() using page_ext
On Mon, Jul 23, 2018 at 12:45:17PM +0300, Kirill A. Shutemov wrote:
> On Wed, Jul 18, 2018 at 04:38:02PM -0700, Dave Hansen wrote:
> > On 07/17/2018 04:20 AM, Kirill A. Shutemov wrote:
> > > Store KeyID in bits 31:16 of extended page flags. These bits are unused.
> >
> > I'd love a two sentence remind of what page_ext is and why you chose to
> > use it. Yes, you need this. No, not everybody that you want to review
> > this patch set knows what it is or why you chose it.
>
> Okay.
>
> > > page_keyid() returns zero until page_ext is ready.
> >
> > Is there any implication of this? Or does it not matter because we
> > don't run userspace until after page_ext initialization is done?
>
> It matters in sense that we shouldn't reference page_ext before it's
> initialized otherwise we will get garbage and crash.
>
> > > page_ext initializer enables static branch to indicate that
> >
> > "enables a static branch"
> >
> > > page_keyid() can use page_ext. The same static branch will gate MKTME
> > > readiness in general.
> >
> > Can you elaborate on this a bit? It would also be a nice place to hint
> > to the folks working hard on the APIs to ensure she checks this.
>
> Okay.

At API init time we can check if (MKTME_ENABLED && mktme_nr_keyids > 0)
Sounds like this is another dependency we need to check and 'wait' on?
It happens after MKTME_ENABLED is set? Let me know.

>
> > > We don't yet set KeyID for the page. It will come in the following
> > > patch that implements prep_encrypted_page(). All pages have KeyID-0 for
> > > now.
> >
> > It also wouldn't hurt to mention why you don't use an X86_FEATURE_* for
> > this rather than an explicit static branch. I'm sure the x86
> > maintainers will be curious.
>
> Sure.
>
> --
> Kirill A. Shutemov

\
 
 \ /
  Last update: 2018-07-23 19:26    [W:0.107 / U:0.244 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site