Re: [PATCH v2 03/11] KVM: nSVM: explicitly raise KVM_REQ_EVENT on nested VM exit if L1 doesn't intercept interrupts

From: Sean Christopherson <seanjc@google.com>
To: Maxim Levitsky <mlevitsk@redhat.com>
Cc: kvm@vger.kernel.org, Sandipan Das <sandipan.das@amd.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Jim Mattson <jmattson@google.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Borislav Petkov <bp@alien8.de>,
	Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Josh Poimboeuf <jpoimboe@kernel.org>,
	Daniel Sneddon <daniel.sneddon@linux.intel.com>,
	Jiaxi Chen <jiaxi.chen@linux.intel.com>,
	Babu Moger <babu.moger@amd.com>,
	linux-kernel@vger.kernel.org, Jing Liu <jing2.liu@intel.com>,
	Wyes Karny <wyes.karny@amd.com>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH v2 03/11] KVM: nSVM: explicitly raise KVM_REQ_EVENT on nested VM exit if L1 doesn't intercept interrupts
Date: Mon, 30 Jan 2023 18:41:19 +0000	[thread overview]
Message-ID: <Y9gPT709jG/9SpSq@google.com> (raw)
In-Reply-To: <Y9RypRsfpLteK51v@google.com>

On Sat, Jan 28, 2023, Sean Christopherson wrote:
> > +	 * If the L2 doesn't intercept interrupts, then
> > +	 * (even if the L2 does use virtual interrupt masking),
> 
> KVM uses "L2" to refer to the thing running at L2.  I think what you are referring
> to here is vmcb12?  And that's controlled by L1.
> 
> > +	 * KVM will use the vmcb02's V_INTR to detect interrupt window.
> 
> s/the vmcb02/vmcb02
> 
> Which of the V_INTR fields does this refer to?  Oooh, you're saying the KVM injects
> a virtual interrupt into L2 using vmcb02 in order to determine when L2 has IRQs
> enabled.
> 
> Why does KVM do that?  Why not pend the actual IRQ directly?

Duh, because KVM needs to gain control in if there are multiple pending events.