linux-kernel - Re: [PATCH, RFC 13/62] x86/mm: Add hooks to allocate and free encrypted pages

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Message-ID: <20190614110458.GN3463@hirez.programming.kicks-ass.net>
Date:   Fri, 14 Jun 2019 13:04:58 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     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 13/62] x86/mm: Add hooks to allocate and free
 encrypted pages

On Fri, Jun 14, 2019 at 11:34:09AM +0200, Peter Zijlstra wrote:
> On Wed, May 08, 2019 at 05:43:33PM +0300, Kirill A. Shutemov wrote:
> 
> > +		lookup_page_ext(page)->keyid = keyid;

> > +		lookup_page_ext(page)->keyid = 0;

Also, perhaps paranoid; but do we want something like:

static inline void page_set_keyid(struct page *page, int keyid)
{
	/* ensure nothing creeps after changing the keyid */
	barrier();
	WRITE_ONCE(lookup_page_ext(page)->keyid, keyid);
	barrier();
	/* ensure nothing creeps before changing the keyid */
}

And this is very much assuming there is no concurrency through the
allocator locks.