linux-kernel - [PATCH v4 09/32] KVM: x86: Handle APICv updates for APIC "mode" changes via request

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Message-ID: <20221001005915.2041642-10-seanjc@google.com>
Date:   Sat,  1 Oct 2022 00:58:52 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alejandro Jimenez <alejandro.j.jimenez@...cle.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Li RongQing <lirongqing@...du.com>
Subject: [PATCH v4 09/32] KVM: x86: Handle APICv updates for APIC "mode"
 changes via request

Use KVM_REQ_UPDATE_APICV to react to APIC "mode" changes, i.e. to handle
the APIC being hardware enabled/disabled and/or x2APIC being toggled.
There is no need to immediately update APICv state, the only requirement
is that APICv be updating prior to the next VM-Enter.

Making a request will allow piggybacking KVM_REQ_UPDATE_APICV to "inhibit"
the APICv memslot when x2APIC is enabled.  Doing that directly from
kvm_lapic_set_base() isn't feasible as KVM's SRCU must not be held when
modifying memslots (to avoid deadlock), and may or may not be held when
kvm_lapic_set_base() is called, i.e. KVM can't do the right thing without
tracking that is rightly buried behind CONFIG_PROVE_RCU=y.

Suggested-by: Maxim Levitsky <mlevitsk@...hat.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/lapic.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 2503f162eb95..316b61b56cca 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2401,7 +2401,7 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value)
 		kvm_apic_set_x2apic_id(apic, vcpu->vcpu_id);

 	if ((old_value ^ value) & (MSR_IA32_APICBASE_ENABLE | X2APIC_ENABLE)) {
-		kvm_vcpu_update_apicv(vcpu);
+		kvm_make_request(KVM_REQ_APICV_UPDATE, vcpu);
 		static_call_cond(kvm_x86_set_virtual_apic_mode)(vcpu);
 	}

-- 
2.38.0.rc1.362.ged0d419d3c-goog