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Date:   Tue, 22 Sep 2020 10:29:18 +0200
From:   Borislav Petkov <bp@alien8.de>
To:     Sean Christopherson <sean.j.christopherson@intel.com>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>, x86@kernel.org,
        linux-sgx@vger.kernel.org, linux-kernel@vger.kernel.org,
        Jethro Beekman <jethro@fortanix.com>,
        Haitao Huang <haitao.huang@linux.intel.com>,
        Chunyang Hui <sanqian.hcy@antfin.com>,
        Jordan Hand <jorhand@linux.microsoft.com>,
        Nathaniel McCallum <npmccallum@redhat.com>,
        Seth Moore <sethmo@google.com>,
        Darren Kenny <darren.kenny@oracle.com>,
        Suresh Siddha <suresh.b.siddha@intel.com>,
        akpm@linux-foundation.org, andriy.shevchenko@linux.intel.com,
        asapek@google.com, cedric.xing@intel.com, chenalexchen@google.com,
        conradparker@google.com, cyhanish@google.com,
        dave.hansen@intel.com, haitao.huang@intel.com,
        josh@joshtriplett.org, kai.huang@intel.com, kai.svahn@intel.com,
        kmoy@google.com, ludloff@google.com, luto@kernel.org,
        nhorman@redhat.com, puiterwijk@redhat.com, rientjes@google.com,
        tglx@linutronix.de, yaozhangx@google.com
Subject: Re: [PATCH v38 14/24] x86/sgx: Add SGX_IOC_ENCLAVE_INIT
Message-ID: <20200922082918.GC22660@zn.tnic>
References: <20200915112842.897265-1-jarkko.sakkinen@linux.intel.com>
 <20200915112842.897265-15-jarkko.sakkinen@linux.intel.com>
 <20200921173514.GI5901@zn.tnic>
 <20200921181021.GA24481@linux.intel.com>
 <20200921182753.GK5901@zn.tnic>
 <20200921191658.GA24823@linux.intel.com>
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On Mon, Sep 21, 2020 at 12:17:00PM -0700, Sean Christopherson wrote:
> That was effectively my original suggestion as well, check for a stale cache
> and retry indefinitely.  I capitulated because it did feel like I was being
> overly paranoid.  I'm obviously ok going the retry indefinitely route :-).
> 
> https://lkml.kernel.org/r/20180904163546.GA5421@linux.intel.com

Right, so if EINIT is so expensive, why does it matter how many cyccles
WRMSR has? I.e., you don't really need to cache - you simply write the 4
MSRs and you're done. Simple.

As to "indefinitely" - caller can increment a counter which counts
how many times it returned SGX_INVALID_EINITTOKEN. I guess when it
reaches some too high number which should not be reached during normal
usage patterns, you can give up and issue a message to say that counter
reached max retries or so but other than that, you should be ok. That
thing is running interruptible in a loop anyway...

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette