linux-kernel - Re: [PATCH, RFC 18/62] x86/mm: Implement syncing per-KeyID direct mappings

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Date:   Sat, 15 Jun 2019 01:43:09 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...capital.net>,
        David Howells <dhowells@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Kai Huang <kai.huang@...ux.intel.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Alison Schofield <alison.schofield@...el.com>,
        linux-mm@...ck.org, kvm@...r.kernel.org, keyrings@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH, RFC 18/62] x86/mm: Implement syncing per-KeyID direct
 mappings

On Fri, Jun 14, 2019 at 11:51:32AM +0200, Peter Zijlstra wrote:
> On Wed, May 08, 2019 at 05:43:38PM +0300, Kirill A. Shutemov wrote:
> > For MKTME we use per-KeyID direct mappings. This allows kernel to have
> > access to encrypted memory.
> > 
> > sync_direct_mapping() sync per-KeyID direct mappings with a canonical
> > one -- KeyID-0.
> > 
> > The function tracks changes in the canonical mapping:
> >  - creating or removing chunks of the translation tree;
> >  - changes in mapping flags (i.e. protection bits);
> >  - splitting huge page mapping into a page table;
> >  - replacing page table with a huge page mapping;
> > 
> > The function need to be called on every change to the direct mapping:
> > hotplug, hotremove, changes in permissions bits, etc.
> 
> And yet I don't see anything in pageattr.c.

You're right. I've hooked up the sync in the wrong place.
> 
> Also, this seems like an expensive scheme; if you know where the changes
> where, a more fine-grained update would be faster.

Do we have any hot enough pageattr users that makes it crucial?

I'll look into this anyway.

-- 
 Kirill A. Shutemov