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.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20221213060912.654668-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/arch/x86/kvm/vmx/vmx_ops.h b/arch/x86/kvm/vmx/vmx_ops.h
index a5282014616c32b65396d011148f5bc7b7e3c277..db95bde52998fcf1d5073876289e535f1eef7f54 100644 (file)
--- 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, KBUILD_MODNAME ": vmread failed: field=%lx\n", field);
        pr_warn_ratelimited(KBUILD_MODNAME ": vmread failed: field=%lx\n", field);
+       instrumentation_end();
        return 0;
 
 do_exception: