linux-kernel - [PATCH 2/7] KVM: VMX: Allow VM-Fail path of VMREAD helper to be instrumented

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Message-ID: <20221213060912.654668-3-seanjc@google.com>
Date:   Tue, 13 Dec 2022 06:09:07 +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,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 2/7] KVM: VMX: Allow VM-Fail path of VMREAD helper to be instrumented

Allow instrumentation in the VM-Fail path of __vmcs_readl() so that the
helper can be used in noinstr functions, e.g. to get the exit reason in
vmx_vcpu_enter_exit() in order to handle NMI VM-Exits in the noinstr
section.  While allowing instrumentation isn't technically safe, KVM has
much bigger problems if VMREAD fails in a noinstr section.

Note, all other VMX instructions also allow instrumentation in their
VM-Fail paths for similar reasons, VMREAD was simply omitted by commit
3ebccdf373c2 ("x86/kvm/vmx: Move guest enter/exit into .noinstr.text")
because VMREAD wasn't used in a noinstr section at the time.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/vmx_ops.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kvm/vmx/vmx_ops.h b/arch/x86/kvm/vmx/vmx_ops.h
index 842dc898c972..5838489e719b 100644
--- a/arch/x86/kvm/vmx/vmx_ops.h
+++ b/arch/x86/kvm/vmx/vmx_ops.h
@@ -100,8 +100,10 @@ static __always_inline unsigned long __vmcs_readl(unsigned long field)
 	return value;

 do_fail:
+	instrumentation_begin();
 	WARN_ONCE(1, "kvm: vmread failed: field=%lx\n", field);
 	pr_warn_ratelimited("kvm: vmread failed: field=%lx\n", field);
+	instrumentation_end();
 	return 0;

 do_exception:
-- 
2.39.0.rc1.256.g54fd8350bd-goog