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

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Date:   Thu, 16 Nov 2023 10:39:56 +0800
From:   Chao Gao <chao.gao@...el.com>
To:     "Li, Xin3" <xin3.li@...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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        "Shankar, Ravi V" <ravi.v.shankar@...el.com>
Subject: Re: [PATCH v1 12/23] KVM: VMX: Handle FRED event data

>> >> >+			default:
>> >> >+				WARN_ON(event_data != 0);
>> >>
>> >> I am not sure if this WARN_ON() can be triggeded by nested VMX. It is
>> >> legitimate for L1 VMM to inject any event w/ an event_data.
>> >>
>> >> FRED spec says:
>> >>
>> >> 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
>> >
>> >5.2.1 Saving Information on the Regular Stack also says:
>> >- For any other event, the event data are not currently defined and
>> >will
>> >  be zero until they are.
>> >
>> >Or you mean something else?
>> 
>> 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