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

Sean Christopherson
2022-12-13T06:09:35Z

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@google.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