linux-kernel - Re: [PATCH v2 0/2] x86/sgx: Limit EPC overcommit

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Message-ID: <YeMaLTtcx9t0+HGG@iki.fi>
Date:   Sat, 15 Jan 2022 21:02:05 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@....fi>
To:     Kristen Carlson Accardi <kristen@...ux.intel.com>
Cc:     linux-sgx@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/2] x86/sgx: Limit EPC overcommit

On Sat, Jan 15, 2022 at 08:57:44PM +0200, Jarkko Sakkinen wrote:
> On Fri, Jan 07, 2022 at 10:16:15AM -0800, Kristen Carlson Accardi wrote:
> > SGX currently allows EPC pages to be overcommitted. If the system is
> > out of enclave memory, EPC pages are swapped to normal RAM via
> > a per enclave shared memory area. This shared memory is not charged
> > to the enclave or the task mapping it, making it hard to account
> > for using normal methods. Since SGX will allow EPC pages to be
> > overcommitted without limits, enclaves can consume system memory
> > for these backing pages without limits.
> > 
> > In order to prevent this, set a cap on the amount of overcommit SGX
> > allows.  Whenever a backing page is requested by an enclave, track
> > the total amount of shared memory pages used across all enclaves and
> > return an error if the overcommit limit has been reached. This will
> > restrict the total amount of backing pages that all enclaves can
> > consume to a maximum amount, and prevent enclaves from consuming
> > all the system RAM for backing pages.
> > 
> > The overcommit percentage has a value of 150, which limits shared
> > memory page consumption to 1.5x the number of EPC pages in the system.
> > 
> > Changes from v1
> > ----------------
> > * removed module parameter and disable boolean
> > * increased over commit percentage to 150% from 100%
> > 
> > Kristen Carlson Accardi (2):
> >   x86/sgx: Add accounting for tracking overcommit
> >   x86/sgx: account backing pages
> > 
> >  arch/x86/kernel/cpu/sgx/encl.c | 76 ++++++++++++++++++++++++++++++++--
> >  arch/x86/kernel/cpu/sgx/encl.h |  6 ++-
> >  arch/x86/kernel/cpu/sgx/main.c | 52 +++++++++++++++++++++--
> >  arch/x86/kernel/cpu/sgx/sgx.h  |  2 +
> >  4 files changed, 128 insertions(+), 8 deletions(-)
> > 
> > -- 
> > 2.20.1
> > 
> 
> I've tested also these. Looking at the feedback, there's
> nothing game changing, so you could add for the next
> version:
> 
> Tested-by: Jarkko Sakkinen <jarkko@...nel.org>

The test environment was a VM running my desktop [*] and I just
run many instances of kselftest as a test case.

[*] i5-9600KF CPU

/Jarkko