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Message-ID: <YAb//EYCkZ7wnl6D@mtj.duckdns.org>
Date: Tue, 19 Jan 2021 10:51:24 -0500
From: Tejun Heo <tj@...nel.org>
To: Vipin Sharma <vipinsh@...gle.com>
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Subject: Re: [Patch v4 1/2] cgroup: svm: Add Encryption ID controller
Hello,
On Fri, Jan 15, 2021 at 08:32:19PM -0800, Vipin Sharma wrote:
> SEV-ES has stronger memory encryption gurantees compared to SEV, apart
> from encrypting the application memory it also encrypts register state
> among other things. In a single host ASIDs can be distributed between
> these two types by BIOS settings.
>
> Currently, Google Cloud has Confidential VM machines offering using SEV.
> ASIDs are not compatible between SEV and SEV-ES, so a VM running on SEV
> cannot run on SEV-ES and vice versa
>
> There are use cases for both types of VMs getting used in future.
Can you please elaborate? I skimmed through the amd manual and it seemed to
say that SEV-ES ASIDs are superset of SEV but !SEV-ES ASIDs. What's the use
case for mixing those two?
> > > > > Other ID types can be easily added in the controller in the same way.
> > > >
> > > > I'm not sure this is necessarily a good thing.
> > >
> > > This is to just say that when Intel and PowerPC changes are ready it
> > > won't be difficult for them to add their controller.
> >
> > I'm not really enthused about having per-hardware-type control knobs. None
> > of other controllers behave that way. Unless it can be abstracted into
> > something common, I'm likely to object.
>
> There was a discussion in Patch v1 and consensus was to have individual
> files because it makes kernel implementation extremely simple.
>
> https://lore.kernel.org/lkml/alpine.DEB.2.23.453.2011131615510.333518@chino.kir.corp.google.com/#t
I'm very reluctant to ack vendor specific interfaces for a few reasons but
most importantly because they usually indicate abstraction and/or the
underlying feature not being sufficiently developed and they tend to become
baggages after a while. So, here are my suggestions:
* If there can be a shared abstraction which hopefully makes intuitive
sense, that'd be ideal. It doesn't have to be one knob but it shouldn't be
something arbitrary to specific vendors.
* If we aren't there yet and vendor-specific interface is a must, attach
that part to an interface which is already vendor-aware.
> This information is not available anywhere else in the system. Only
> other way to get this value is to use CPUID instruction (0x8000001F) of
> the processor. Which also has disdvantage if sev module in kernel
> doesn't use all of the available ASIDs for its work (right now it uses
> all) then there will be a mismatch between what user get through their
> code and what is actually getting used in the kernel by sev.
>
> In cgroup v2, I didn't see current files for other cgroups in root
> folder that is why I didn't show that file in root folder.
>
> Will you be fine if I show two files in the root, something like:
>
> encids.sev.capacity
> encids.sev.current
>
> In non root folder, it will be:
> encids.sev.max
> encids.sev.current
>
> I still prefer encids.sev.stat, as it won't repeat same information in
> each cgroup but let me know what you think.
Yeah, this will be a first and I was mostly wondering about the same number
appearing under different files / names on root and !root cgroups. I'm
leaning more towards capacity/current but let me think about it a bit more.
Thank you.
--
tejun
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