linux-kernel - [PATCH] KVM: x86: Use SRCU to protect zap in __kvm_set_or_clear_apicv

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Message-ID: <20221102193020.1091939-1-bgardon@google.com>
Date:   Wed,  2 Nov 2022 19:30:20 +0000
From:   Ben Gardon <bgardon@...gle.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Anish Ghulati <aghulati@...gle.com>,
        Ben Gardon <bgardon@...gle.com>
Subject: [PATCH] KVM: x86: Use SRCU to protect zap in __kvm_set_or_clear_apicv_inhibit

kvm_zap_gfn_range must be called in an SRCU read-critical section, but
there is no SRCU annotation in __kvm_set_or_clear_apicv_inhibit.
Add the needed SRCU annotation.

Tested: ran tools/testing/selftests/kvm/x86_64/debug_regs on a DBG
	build. This patch causes the suspicious RCU warning to disappear.
	Note that the warning is hit in __kvm_zap_rmaps, so
	kvm_memslots_have_rmaps must return true in order for this to
	repro (i.e. the TDP MMU must be off or nesting in use.)

Fixes: 36222b117e36 ("KVM: x86: don't disable APICv memslot when inhibited")
Signed-off-by: Ben Gardon <bgardon@...gle.com>
---
 arch/x86/kvm/x86.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index cd9eb13e2ed7..6d853e5f683d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10091,7 +10091,10 @@ void __kvm_set_or_clear_apicv_inhibit(struct kvm *kvm,
 		kvm->arch.apicv_inhibit_reasons = new;
 		if (new) {
 			unsigned long gfn = gpa_to_gfn(APIC_DEFAULT_PHYS_BASE);
+			int idx = srcu_read_lock(&kvm->srcu);
+
 			kvm_zap_gfn_range(kvm, gfn, gfn+1);
+			srcu_read_unlock(&kvm->srcu, idx);
 		}
 	} else {
 		kvm->arch.apicv_inhibit_reasons = new;
-- 
2.38.1.431.g37b22c650d-goog