Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 31 Aug 2022 05:57:22 +0300
From:   "jarkko@kernel.org" <jarkko@kernel.org>
To:     "Huang, Kai" <kai.huang@intel.com>
Cc:     "pmenzel@molgen.mpg.de" <pmenzel@molgen.mpg.de>,
        "linux-sgx@vger.kernel.org" <linux-sgx@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        "Dhanraj, Vijay" <vijay.dhanraj@intel.com>,
        "Chatre, Reinette" <reinette.chatre@intel.com>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "bp@alien8.de" <bp@alien8.de>,
        "haitao.huang@linux.intel.com" <haitao.huang@linux.intel.com>,
        "hpa@zytor.com" <hpa@zytor.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/6] x86/sgx: Do not consider unsanitized pages an error
Message-ID: <Yw7OEh7QP8tb7BR1@kernel.org>
References: <20220830031206.13449-1-jarkko@kernel.org>
 <20220830031206.13449-2-jarkko@kernel.org>
 <1f43e7b9-c101-3872-bd1b-add66933b285@intel.com>
 <1b3308a364317d36ad41961ea9cfee24aa122f02.camel@intel.com>
 <Yw7EX5GCrEaLzpHV@kernel.org>
 <d07577c3f0b4b3fff0ce470c56f91fb634653703.camel@intel.com>
 <Yw7LJa7eRG+WZ0wv@kernel.org>
 <c3c085d69311ed759bff5bb325a2c182d423f91f.camel@intel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <c3c085d69311ed759bff5bb325a2c182d423f91f.camel@intel.com>
Precedence: bulk

On Wed, Aug 31, 2022 at 02:55:52AM +0000, Huang, Kai wrote:
> On Wed, 2022-08-31 at 05:44 +0300, jarkko@kernel.org wrote:
> > On Wed, Aug 31, 2022 at 02:35:53AM +0000, Huang, Kai wrote:
> > > On Wed, 2022-08-31 at 05:15 +0300, jarkko@kernel.org wrote:
> > > > On Wed, Aug 31, 2022 at 01:27:58AM +0000, Huang, Kai wrote:
> > > > > On Tue, 2022-08-30 at 15:54 -0700, Reinette Chatre wrote:
> > > > > > Hi Jarkko,
> > > > > > 
> > > > > > On 8/29/2022 8:12 PM, Jarkko Sakkinen wrote:
> > > > > > > In sgx_init(), if misc_register() for the provision device fails, and
> > > > > > > neither sgx_drv_init() nor sgx_vepc_init() succeeds, then ksgxd will be
> > > > > > > prematurely stopped.
> > > > > > 
> > > > > > I do not think misc_register() is required to fail for the scenario to
> > > > > > be triggered (rather use "or" than "and"?). Perhaps just
> > > > > > "In sgx_init(), if a failure is encountered after ksgxd is started
> > > > > > (via sgx_page_reclaimer_init()) ...".
> > > > > 
> > > > > IMHO "a failure" might be too vague.  For instance, failure to sgx_drv_init()
> > > > > won't immediately result in ksgxd to stop prematurally.  As long as KVM SGX can
> > > > > be initialized successfully, sgx_init() still returns 0.
> > > > > 
> > > > > Btw I was thinking whether we should move sgx_page_reclaimer_init() to the end
> > > > > of sgx_init(), after we make sure at least one of the driver and the KVM SGX is
> > > > > initialized successfully.  Then the code change in this patch won't be necessary
> > > > > if I understand correctly.  AFAICT there's no good reason to start the ksgxd at
> > > > > early stage before we are sure either the driver or KVM SGX will work.
> > > > 
> > > > I would focus fixing the existing flow rather than reinventing the flow.
> > > > 
> > > > It can be made to work, and therefore it is IMHO correct action to take.
> > > 
> > > From another perspective, the *existing flow* is the reason which causes this
> > > bug.  A real fix is to fix the flow itself.
> > 
> > Any existing flow in part of the kernel can have a bug. That
> > does not mean that switching flow would be proper way to fix
> > a bug.
> > 
> > BR, Jarkko
> 
> Yes but I think this is only true when the flow is reasonable.  If the flow
> itself isn't reasonable, we should fix the flow (given it's easy to fix AFAICT).
> 
> Anyway, let us also hear from others.

The flow can be made to work without issues, which in the
context of a bug fix is exactly what a bug fix should do.
Not more or less.

You don't gain any measurable value for the user with this
switch idea.

BR, Jarkko