linux-kernel - Re: [PATCH v8 2/5] x86/tdx: Add TDX Guest event notify interrupt support

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Message-ID: <97ace776b756312de05d3a9c8b1ca251e714db17.camel@intel.com>
Date:   Thu, 23 Jun 2022 22:24:29 +1200
From:   Kai Huang <kai.huang@...el.com>
To:     Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org
Cc:     "H . Peter Anvin" <hpa@...or.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Wander Lairson Costa <wander@...hat.com>,
        Isaku Yamahata <isaku.yamahata@...il.com>,
        marcelo.cerri@...onical.com, tim.gardner@...onical.com,
        khalid.elmously@...onical.com, philip.cox@...onical.com,
        linux-kernel@...r.kernel.org,
        "Nakajima, Jun" <jun.nakajima@...el.com>
Subject: Re: [PATCH v8 2/5] x86/tdx: Add TDX Guest event notify interrupt
 support

On Mon, 2022-06-20 at 08:44 -0700, Sathyanarayanan Kuppuswamy wrote:
> I agree that event notification is currently only used for attestation. But I
> think in future there could be other use cases for it. 
> 

We have TDVMCALL<Service> in GHCI 1.5.  It allows specifying the vector.  I
don't know whether there's any future case that still needs
SetupEventNotifyInterrupt.

> If the intention is just
> to use it for attestation, then we can just modify the GetQuote TDVMCALL to pass
> the vector address, and there is no need for new TDVMCALL. 

The TDVMCALL<Service> in GHCI 1.5 actually supports specifying the vector.  It
currently neither clearly says "the VMM should inject event to the vCPU on which
the TDVMCALL<Service> is called", nor it allows specifying which vCPU to inject.
Assuming we can lobby (I am already lobbying, actually) to make either way, in
fact I think it can be used as IRQ way (like I described in my first reply).

I once lobbied to completely remove GetQuote (and SetupEventNotifyInterrupt)
from GHCI 1.0 and move TDVMCALL<Service> from GHCI 1.5 to 1.0, and define a new
sub-service for attestation -- GetQuote will be one command then, and we can
define more attestation related commands (which is likely) when needed.  I
believe using TDVMCALL<Service> for GetQuote can actually allow kernel to use
IRQ way, but doesn't need a system vector.  But this wasn't successful.

-- 
Thanks,
-Kai