linux-kernel - Re: [PATCH v2 1/3] x86/tdx: Add TDX Guest event notify interrupt support

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Message-ID: <11b38df4d91b1a85cec500d5fae9ab2242361f52.camel@intel.com>
Date:   Fri, 28 Apr 2023 13:50:51 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "corbet@....net" <corbet@....net>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "shuah@...nel.org" <shuah@...nel.org>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "x86@...nel.org" <x86@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>
CC:     "Yu, Guorui" <guorui.yu@...ux.alibaba.com>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "wander@...hat.com" <wander@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "chongc@...gle.com" <chongc@...gle.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "qinkun@...che.org" <qinkun@...che.org>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Aktas, Erdem" <erdemaktas@...gle.com>,
        "dionnaglaze@...gle.com" <dionnaglaze@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "Du, Fan" <fan.du@...el.com>
Subject: Re: [PATCH v2 1/3] x86/tdx: Add TDX Guest event notify interrupt
 support

On Tue, 2023-04-25 at 23:07 -0700, Sathyanarayanan Kuppuswamy wrote:
> > > +/**
> > > + * tdx_event_irq_init() - Register IRQ for event notification from the
> > > VMM to
> > > + *                       the TDX Guest.
> > > + *
> > > + * Use SetupEventNotifyInterrupt TDVMCALL to register the event
> > > notification
> > > + * IRQ with the VMM, which is used by the VMM to notify the TDX guest
> > > when
> > > + * needed, for instance, when VMM finishes the GetQuote request from the
> > > TDX
> > > + * guest. The VMM always notifies the TDX guest via the same CPU on which
> > > the
> > > + * SetupEventNotifyInterrupt TDVMCALL is called. For simplicity, just
> > > allocate
> > > + * an IRQ (and a vector) directly from x86_vector_domain for such
> > > notification
> > > + * and pin the IRQ to the same CPU on which TDVMCALL is called.
> > 
> > I think "for simplicity" applies to allocate IRQ/vector "from BSP using
> > early_initcall()" (so TDVMCALL is easily guaranteed to be called on the same
> > cpu
> > where vector is allocated), but doesn't apply to allocate IRQ/vector from
> > x86_vector_domain and "pin the IRQ to the same CPU on which TDVMCALAL is
> > called".  The latter is something you must do (otherwise you need to
> > allocate
> > the same vector on all cpus), but not something that you do "for
> > simplicity".
> > 
> > > + *
> > > + * Since tdx_event_irq_init() is triggered via early_initcall(), it will
> > > be
> > > + * called before secondary CPUs bring up, so no special logic is required
> > > to
> > > + * ensure that the same CPU is used for SetupEventNotifyInterrupt
> > > TDVMCALL and
> > > + * IRQ allocation.
> > 
> > IMHO the second paragraph is obvious and no need to mention.
> > 
> > As explained above, I guess you just need to at somewhere simply mention
> > something like: "for simplicity use early_initcall() to allocate and pin the
> > IRQ/vector on BSP and also call the TDVMCALL on BSP".  Or probably "also
> > call
> > the TDVMCALL on BSP" can also be omitted as it's kinda already explained in
> > the
> > nature of the TDVMCALL.
> 
> How about the following?
> 
> Use SetupEventNotifyInterrupt TDVMCALL to register the event notification
> IRQ with the VMM, which is used by the VMM to notify the TDX guest when
> needed, for instance, when VMM finishes the GetQuote request from the TDX
> guest. The VMM always notifies the TDX guest via the same CPU that calls the
> SetupEventNotifyInterrupt TDVMCALL. Allocate an IRQ/vector from the
> x86_vector_domain and pin it on the same CPU on which TDVMCALL is called.
> For simplicity, use early_initcall() to allow both IRQ allocation and
> TDVMCALL to use BSP.

Sorry I missed your reply.  OK to me.