Complement commit 4289d2728664 ("KVM: retpolines: x86: eliminate
retpoline from vmx.c exit handlers") and avoid a retpoline call for
control register accesses as well.
This speeds up guests that make heavy use of it, like grsecurity
kernels toggling CR0.WP to implement kernel W^X.
Signed-off-by: Mathias Krause <minipli@xxxxxxxxxxxxxx>
---
Meanwhile I got my hands on a AMD system and while doing a similar change
for SVM gives a small measurable win (1.1% faster for grsecurity guests),
it would provide nothing for other guests, as the change I was testing was
specifically targeting CR0 caused exits.
A more general approach would instead cover CR3 and, maybe, CR4 as well.
However, that would require a lot more exit code compares, likely
vanishing the gains in the general case. So this tweak is VMX only.
arch/x86/kvm/vmx/vmx.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index c788aa382611..c8198c8a9b55 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6538,6 +6538,8 @@ static int __vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
return handle_external_interrupt(vcpu);
else if (exit_reason.basic == EXIT_REASON_HLT)
return kvm_emulate_halt(vcpu);
+ else if (exit_reason.basic == EXIT_REASON_CR_ACCESS)
+ return handle_cr(vcpu);
else if (exit_reason.basic == EXIT_REASON_EPT_MISCONFIG)
return handle_ept_misconfig(vcpu);
#endif
--
2.39.1
