linux-kernel - Re: [PATCH v2] sparc64: Add support for Application Data Integrity (ADI)

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Message-ID: <56DDF3C4.7070701@oracle.com>
Date:	Mon, 7 Mar 2016 14:33:56 -0700
From:	Khalid Aziz <khalid.aziz@...cle.com>
To:	David Miller <davem@...emloft.net>
Cc:	rob.gardner@...cle.com, corbet@....net, akpm@...ux-foundation.org,
	dingel@...ux.vnet.ibm.com, bob.picco@...cle.com,
	kirill.shutemov@...ux.intel.com, aneesh.kumar@...ux.vnet.ibm.com,
	aarcange@...hat.com, arnd@...db.de, sparclinux@...r.kernel.org,
	mhocko@...e.cz, chris.hyser@...cle.com, richard@....at,
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	gthelen@...gle.com, jack@...e.cz, xiexiuqi@...wei.com,
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	bsegall@...gle.com, geert@...ux-m68k.org, dave@...olabs.net,
	adobriyan@...il.com, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-arch@...r.kernel.org, linux-api@...r.kernel.org
Subject: Re: [PATCH v2] sparc64: Add support for Application Data Integrity
 (ADI)

On 03/07/2016 12:16 PM, David Miller wrote:
> From: Khalid Aziz <khalid.aziz@...cle.com>
> Date: Mon, 7 Mar 2016 11:24:54 -0700
>
>> Tags can be cleared by user by setting tag to 0. Tags are
>> automatically cleared by the hardware when the mapping for a virtual
>> address is removed from TSB (which is why swappable pages are a
>> problem), so kernel does not have to do it as part of clean up.
>
> You might be able to crib some bits for the Tag in the swp_entry_t, it's
> 64-bit and you can therefore steal bits from the offset field.
>
> That way you'll have the ADI tag in the page tables, ready to re-install
> at swapin time.
>

That is a possibility but limited in scope. An address range covered by 
a single TTE can have large number of tags. Version tags are set on 
cacheline. In extreme case, one could set a tag for each set of 64-bytes 
in a page. Also tags are set completely in userspace and no transition 
occurs to kernel space, so kernel has no idea of what tags have been 
set. I have not found a way to query the MMU on tags.

I will think some more about it.

Thanks,
Khalid