linux-kernel - Re: [PATCH] x86/mm: Decouple dynamic __PHYSICAL

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Message-ID: <20180214042121.tza3cpvrnpztjeme@node.shutemov.name>
Date:   Wed, 14 Feb 2018 07:21:21 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Kai Huang <kai.huang@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/mm: Decouple dynamic __PHYSICAL_MASK from AMD SME

On Tue, Feb 13, 2018 at 10:10:22PM -0600, Tom Lendacky wrote:
> On 2/8/2018 6:55 AM, Kirill A. Shutemov wrote:
> > AMD SME claims one bit from physical address to indicate whether the
> > page is encrypted or not. To achieve that we clear out the bit from
> > __PHYSICAL_MASK.
> 
> I was actually working on a suggestion by Linus to use one of the software
> page table bits to indicate encryption and translate that to the hardware
> bit when writing the actual page table entry.  With that, __PHYSICAL_MASK
> would go back to its original definition.

But you would need to mask it on reading of pfn from page table entry,
right? I expect it to have more overhead than this one.

And software bits are valuable. Do we still have a spare one for this?

-- 
 Kirill A. Shutemov