linux-kernel - Re: [PATCH v38 14/24] x86/sgx: Add SGX_IOC_ENCLAVE

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Date:   Tue, 22 Sep 2020 10:29:18 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>, x86@...nel.org,
        linux-sgx@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jethro Beekman <jethro@...tanix.com>,
        Haitao Huang <haitao.huang@...ux.intel.com>,
        Chunyang Hui <sanqian.hcy@...fin.com>,
        Jordan Hand <jorhand@...ux.microsoft.com>,
        Nathaniel McCallum <npmccallum@...hat.com>,
        Seth Moore <sethmo@...gle.com>,
        Darren Kenny <darren.kenny@...cle.com>,
        Suresh Siddha <suresh.b.siddha@...el.com>,
        akpm@...ux-foundation.org, andriy.shevchenko@...ux.intel.com,
        asapek@...gle.com, cedric.xing@...el.com, chenalexchen@...gle.com,
        conradparker@...gle.com, cyhanish@...gle.com,
        dave.hansen@...el.com, haitao.huang@...el.com,
        josh@...htriplett.org, kai.huang@...el.com, kai.svahn@...el.com,
        kmoy@...gle.com, ludloff@...gle.com, luto@...nel.org,
        nhorman@...hat.com, puiterwijk@...hat.com, rientjes@...gle.com,
        tglx@...utronix.de, yaozhangx@...gle.com
Subject: Re: [PATCH v38 14/24] x86/sgx: Add SGX_IOC_ENCLAVE_INIT

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