From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 32ECCC43334 for ; Tue, 4 Sep 2018 14:54:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DA90E2086C for ; Tue, 4 Sep 2018 14:54:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DA90E2086C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727536AbeIDTUT (ORCPT ); Tue, 4 Sep 2018 15:20:19 -0400 Received: from mga18.intel.com ([134.134.136.126]:17925 "EHLO mga18.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726004AbeIDTUT (ORCPT ); Tue, 4 Sep 2018 15:20:19 -0400 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by orsmga106.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 04 Sep 2018 07:54:52 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.53,329,1531810800"; d="scan'208";a="85910668" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.20]) by fmsmga004.fm.intel.com with ESMTP; 04 Sep 2018 07:54:51 -0700 Date: Tue, 4 Sep 2018 07:54:51 -0700 From: Sean Christopherson To: "Huang, Kai" Cc: Jarkko Sakkinen , "platform-driver-x86@vger.kernel.org" , "x86@kernel.org" , "nhorman@redhat.com" , "linux-kernel@vger.kernel.org" , "tglx@linutronix.de" , "suresh.b.siddha@intel.com" , "Ayoun, Serge" , "hpa@zytor.com" , "npmccallum@redhat.com" , "mingo@redhat.com" , "linux-sgx@vger.kernel.org" , "Hansen, Dave" Subject: Re: [PATCH v13 10/13] x86/sgx: Add sgx_einit() for initializing enclaves Message-ID: <20180904145451.GA5233@linux.intel.com> References: <20180827185507.17087-1-jarkko.sakkinen@linux.intel.com> <20180827185507.17087-11-jarkko.sakkinen@linux.intel.com> <1535406078.3416.9.camel@intel.com> <20180828070129.GA5301@linux.intel.com> <105F7BF4D0229846AF094488D65A09893541037C@PGSMSX112.gar.corp.intel.com> <20180831121645.GA18075@linux.intel.com> <20180831181509.GB21555@linux.intel.com> <20180903191926.GC13497@linux.intel.com> <105F7BF4D0229846AF094488D65A09893541970F@PGSMSX112.gar.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <105F7BF4D0229846AF094488D65A09893541970F@PGSMSX112.gar.corp.intel.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 03, 2018 at 04:45:14PM -0700, Huang, Kai wrote: > > -----Original Message----- > > From: linux-sgx-owner@vger.kernel.org [mailto:linux-sgx- > > owner@vger.kernel.org] On Behalf Of Jarkko Sakkinen > > Sent: Tuesday, September 4, 2018 7:19 AM > > To: Christopherson, Sean J > > Cc: Huang, Kai ; platform-driver-x86@vger.kernel.org; > > x86@kernel.org; nhorman@redhat.com; linux-kernel@vger.kernel.org; > > tglx@linutronix.de; suresh.b.siddha@intel.com; Ayoun, Serge > > ; hpa@zytor.com; npmccallum@redhat.com; > > mingo@redhat.com; linux-sgx@vger.kernel.org; Hansen, Dave > > > > Subject: Re: [PATCH v13 10/13] x86/sgx: Add sgx_einit() for initializing enclaves > > > > On Fri, Aug 31, 2018 at 11:15:09AM -0700, Sean Christopherson wrote: > > > On Fri, Aug 31, 2018 at 03:17:03PM +0300, Jarkko Sakkinen wrote: > > > > 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. > > > > > > Tracking the validity of the cache means we're hosed if we miss any > > > condition that causes the MSRs to be reset. I think we're better off > > > assuming the cache can be stale at any time, i.e. don't track power > > > cyles and instead handle EINIT failure due to INVALID_TOKEN by writing > > > the cache+MSRs with the desired hash and retrying EINIT. EINIT is > > > interruptible and its latency is extremely variable in any case, e.g. > > > tens of thousands of cycles, so this rarely-hit "slow path" probably > > > wouldn't affect the worst case latency of EINIT. > > > > Sounds a good refiniment. Pretty good solution to heal from host sleep on the > > guest VM and then there is no need for driver changes. > > To me either way should be OK, keeping MSR cache or retrying EINIT, since EINIT should not be in performance critical path I think. > > But INVALID_TOKEN is not only returned when MSRs are mismatched, so do you plan to check to rule out other cases that cause INVALID_TOKEN before retrying EINIT, or unconditionally retry EINIT? And we should only retry once? I don't see any value in trying to rule out specific causes of INVALID_TOKEN, but we should only retry EINIT if ret==INVALID_TOKEN and RDMSR(HASH0) != sgx_lepubkeyhash[0]. Only the first MSR needs to be checked for validity as they're a package deal, i.e. they'll all be valid or all be reset. There shouldn't be a limit on retry attempts, e.g. the MSRs could theoretically be reset between WRMSR and EINIT. > > Thanks, > -Kai > > > > /Jarkko