linux-kernel - Re: [PATCH v13 10/13] x86/sgx: Add sgx

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Date:   Fri, 31 Aug 2018 15:17:03 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     "Huang, Kai" <kai.huang@...el.com>
Cc:     "platform-driver-x86@...r.kernel.org" 
        <platform-driver-x86@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "nhorman@...hat.com" <nhorman@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Christopherson, Sean J" <sean.j.christopherson@...el.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "suresh.b.siddha@...el.com" <suresh.b.siddha@...el.com>,
        "Ayoun, Serge" <serge.ayoun@...el.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "npmccallum@...hat.com" <npmccallum@...hat.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
        "Hansen, Dave" <dave.hansen@...el.com>
Subject: Re: [PATCH v13 10/13] x86/sgx: Add sgx_einit() for initializing
 enclaves

On Wed, Aug 29, 2018 at 07:33:54AM +0000, Huang, Kai wrote:
> [snip..]
> 
> > > >
> > > > @@ -38,6 +39,18 @@ static LIST_HEAD(sgx_active_page_list);  static
> > > > DEFINE_SPINLOCK(sgx_active_page_list_lock);
> > > >  static struct task_struct *ksgxswapd_tsk;  static
> > > > DECLARE_WAIT_QUEUE_HEAD(ksgxswapd_waitq);
> > > > +static struct notifier_block sgx_pm_notifier; static u64
> > > > +sgx_pm_cnt;
> > > > +
> > > > +/* The cache for the last known values of IA32_SGXLEPUBKEYHASHx
> > > > +MSRs
> > > > for each
> > > > + * CPU. The entries are initialized when they are first used by
> > > > sgx_einit().
> > > > + */
> > > > +struct sgx_lepubkeyhash {
> > > > +	u64 msrs[4];
> > > > +	u64 pm_cnt;
> > >
> > > May I ask why do we need pm_cnt here? In fact why do we need suspend
> > > staff (namely, sgx_pm_cnt above, and related code in this patch) here
> > > in this patch? From the patch commit message I don't see why we need
> > > PM staff here. Please give comment why you need PM staff, or you may
> > > consider to split the PM staff to another patch.
> > 
> > Refining the commit message probably makes more sense because without PM
> > code sgx_einit() would be broken. The MSRs have been reset after waking up.
> > 
> > Some kind of counter is required to keep track of the power cycle. When going
> > to sleep the sgx_pm_cnt is increased. sgx_einit() compares the current value of
> > the global count to the value in the cache entry to see whether we are in a new
> > power cycle.
> 
> You mean reset to Intel default? I think we can also just reset the
> cached MSR values on each power cycle, which would be simpler, IMHO?

I don't really see that much difference in the complexity.

> I think we definitely need some code to handle S3-S5, but should be in
> separate patches, since I think the major impact of S3-S5 is entire
> EPC being destroyed. I think keeping pm_cnt is not sufficient enough
> to handle such case?

The driver has SGX_POWER_LOST_ENCLAVE for ioctls and it deletes the TCS
entries.

> > This brings up one question though: how do we deal with VM host going to sleep?
> > VM guest would not be aware of this.
> 
> IMO VM just gets "sudden loss of EPC" after suspend & resume in host.
> SGX driver and SDK should be able to handle "sudden loss of EPC", ie,
> co-working together to re-establish the missing enclaves.

This is not about EPC. It is already dealt by the driver. I'm concerned
about the MSR cache as it would mess up.

But I guess this logic is part of the KVM code anyway now that I think
more of it.

/Jarkko