Patch "KVM: retpolines: x86: eliminate retpoline from vmx.c exit handlers" has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    KVM: retpolines: x86: eliminate retpoline from vmx.c exit handlers

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     kvm-retpolines-x86-eliminate-retpoline-from-vmx.c-ex.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 3c1597d7ec45ff271a75103e2981fc3b6c58a96d
Author: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Date:   Mon Nov 4 17:59:59 2019 -0500

    KVM: retpolines: x86: eliminate retpoline from vmx.c exit handlers
    
    [ Upstream commit 4289d2728664fc1fb49cfc76a6a7d96d913b921f ]
    
    It's enough to check the exit value and issue a direct call to avoid
    the retpoline for all the common vmexit reasons.
    
    Of course CONFIG_RETPOLINE already forbids gcc to use indirect jumps
    while compiling all switch() statements, however switch() would still
    allow the compiler to bisect the case value. It's more efficient to
    prioritize the most frequent vmexits instead.
    
    The halt may be slow paths from the point of the guest, but not
    necessarily so from the point of the host if the host runs at full CPU
    capacity and no host CPU is ever left idle.
    
    Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
    Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
    Stable-dep-of: 31de69f4eea7 ("KVM: nVMX: Properly expose ENABLE_USR_WAIT_PAUSE control to L1")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 0fae9b448ab9..668505c6abe9 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6015,9 +6015,23 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu)
 	}
 
 	if (exit_reason < kvm_vmx_max_exit_handlers
-	    && kvm_vmx_exit_handlers[exit_reason])
+	    && kvm_vmx_exit_handlers[exit_reason]) {
+#ifdef CONFIG_RETPOLINE
+		if (exit_reason == EXIT_REASON_MSR_WRITE)
+			return kvm_emulate_wrmsr(vcpu);
+		else if (exit_reason == EXIT_REASON_PREEMPTION_TIMER)
+			return handle_preemption_timer(vcpu);
+		else if (exit_reason == EXIT_REASON_PENDING_INTERRUPT)
+			return handle_interrupt_window(vcpu);
+		else if (exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
+			return handle_external_interrupt(vcpu);
+		else if (exit_reason == EXIT_REASON_HLT)
+			return kvm_emulate_halt(vcpu);
+		else if (exit_reason == EXIT_REASON_EPT_MISCONFIG)
+			return handle_ept_misconfig(vcpu);
+#endif
 		return kvm_vmx_exit_handlers[exit_reason](vcpu);
-	else {
+	} else {
 		vcpu_unimpl(vcpu, "vmx: unexpected exit reason 0x%x\n",
 				exit_reason);
 		dump_vmcs();