linux-kernel - Re: [PATCH v3 0/5] x86: Show in sysfs if a memory node is able to do encryption

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Message-ID: <9ab81982-d2f1-01ac-959a-50683f4c2a05@intel.com>
Date:   Tue, 7 Dec 2021 12:13:49 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Martin Fernandez <martin.fernandez@...ypsium.com>,
        Richard Hughes <hughsient@...il.com>,
        linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
        platform-driver-x86@...r.kernel.org, linux-mm@...ck.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        ardb@...nel.org, dvhart@...radead.org, andy@...radead.org,
        gregkh@...uxfoundation.org, rafael@...nel.org,
        akpm@...ux-foundation.org, daniel.gutson@...ypsium.com,
        alex.bazhaniuk@...ypsium.com, alison.schofield@...el.com
Subject: Re: [PATCH v3 0/5] x86: Show in sysfs if a memory node is able to do
 encryption

On 12/7/21 12:06 PM, Mike Rapoport wrote:
>> An ABI that says "everything is encrypted" is pretty meaningless and
>> only useful for this one, special case.
>>
>> A per-node ABI is useful for this case and is also useful going forward
>> if folks want to target allocations from applications to NUMA nodes
>> which have encryption capabilities.  The ABI in this set is useful for
>> the immediate case and is useful to other folks.
> I don't mind per-node ABI, I'm just concerned that having a small region
> without the encryption flag set will render the entire node "not
> encryptable". This may happen because a bug in firmware, a user that shoot
> themself in a leg with weird memmap= or some hidden gem in interaction
> between e820, EFI and memblock that we still didn't discover.

That's a good point.  But, that seems more in the realm of a
pr_{info,warn}_once() than something deserving of its own specific ABI.

If we have a 100GB of a node that supports encryption, and 4k that
causes the whole thing to be considered un-encryptable, a warning is be
appropriate and feasible.