linux-kernel - Re: [PATCH] [v2] x86/sgx: Allow enclaves to use Asynchrounous Exit Notification

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Message-ID: <06a9fef8579e880b9b031f03911739d4d902dbe0.camel@intel.com>
Date:   Mon, 25 Jul 2022 22:36:17 +1200
From:   Kai Huang <kai.huang@...el.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     Jarkko Sakkinen <jarkko@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Haitao Huang <haitao.huang@...ux.intel.com>, x86@...nel.org,
        linux-sgx@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [v2] x86/sgx: Allow enclaves to use Asynchrounous Exit
 Notification

On Fri, 2022-07-22 at 08:21 -0700, Dave Hansen wrote:
> On 7/22/22 06:26, Kai Huang wrote:
> > Did a quick look at the spec.  It appears ENCLU[EDECCSSA] should be used
> > together with AEX-notify.  So besides advertising the new
> > SGX_ATTR_ASYNC_EXIT_NOTIFY bit to the KVM guest, I think we should also
> > advertise the ENCLU[EDECCSSA] support in guest's CPUID, like below (untested)?
> 
> Sounds like a great follow-on patch!  It doesn't seem truly functionally
> required from the spec:
> 
> > EDECCSSA is a new Intel SGX user leaf function
> > (ENCLU[EDECCSSA]) that can facilitate AEX notification handling...
> 
> If that's wrong or imprecise, I'd love to hear more about it and also
> about how the spec will be updated.
> 

They are enumerated separately, but looks in practice the notify handler will
use it to switch back to the correct/targeted CSSA to continue to run normally
after handling the exit notify.  This is my understanding of the "facilitate"
mean in the spec.

Btw, in real hardware I think the two should come together, meaning no real
hardware will only support one. 

Haitao, could you give us more information?

-- 
Thanks,
-Kai