linux-kernel - RE: [PATCH v1 12/23] KVM: VMX: Handle FRED event data

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Date:   Mon, 20 Nov 2023 08:16:48 +0000
From:   "Li, Xin3" <xin3.li@...el.com>
To:     "Gao, Chao" <chao.gao@...el.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
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        "peterz@...radead.org" <peterz@...radead.org>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>
Subject: RE: [PATCH v1 12/23] KVM: VMX: Handle FRED event data

> >> IIUC, L1 KVM can inject a nested exception whose vector isn't #DB, or
> >> #NM or #PF with a non-zero event_data to L2.
> >
> >No, this is not allowed.
> 
> How do you interpret the last sentence:
> 
> 	Section 5.2.1 specifies the event data that FRED event delivery of
> 	certain events saves on the stack. When FRED event delivery is used
> 	for an event injected by VM entry, the event data saved is the value
> 	of the injected-event-data field in the VMCS. This value is used
> 	instead of what is specified in Section 5.2.1 and is done for __ALL__
> 	injected events using FRED event delivery

To me, it means FRED event injection during VM entry simply pushes the
value in the injected-event-data field of the VMCS as event data.  But
the event data definition should comply with Section 5.2.1.  It is a
forward compatibility issue otherwise.