Re: [PATCH v38 14/24] x86/sgx: Add SGX_IOC_ENCLAVE_INIT

[Jarkko Sakkinen]

On Tue, Sep 22, 2020 at 10:29:18AM +0200, Borislav Petkov wrote:
> 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@xxxxxxxxxxxxxxx
> 
> 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...

The way I see it after reading the thread is:

1. Start with simpler always-update-MSRs in this patch set.
2. If this ever causes a bottleneck, then we will fix it.

> Thx.
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette

/Jarkko