On 17/04/2018 17:46, Christopherson, Sean J wrote:
> On Tue, 2018-04-17, Zdenek Kaspar wrote:
>> Hello, I did quick test with latest stable kernel (4.16.2) and got tons
>> of vmwrite errors immediately when starting VM:
>
> Code related to UMIP emulation is effectively doing an unconditional
> RMW on SECONDARY_VM_EXEC_CONTROL, which isn't guaranteed to exist on
> older processors. KVM already ensures it only advertises UMIP (via
> emulation) when SECONDARY_EXEC_DESC can be set, i.e. KVM is already
> implicitly checking for SECONDARY_VM_EXEC_CONTROL, so fixing the bug
> is just a matter of omitting the unneeded VMREAD/VMWRITE sequence.
Thanks for the report!
This should be a fix:
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index aa66ccd6ed6c..c5dd185825c7 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -4767,14 +4767,16 @@ static int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
else
hw_cr4 |= KVM_PMODE_VM_CR4_ALWAYS_ON;
- if ((cr4 & X86_CR4_UMIP) && !boot_cpu_has(X86_FEATURE_UMIP)) {
- vmcs_set_bits(SECONDARY_VM_EXEC_CONTROL,
- SECONDARY_EXEC_DESC);
- hw_cr4 &= ~X86_CR4_UMIP;
- } else if (!is_guest_mode(vcpu) ||
- !nested_cpu_has2(get_vmcs12(vcpu), SECONDARY_EXEC_DESC))
- vmcs_clear_bits(SECONDARY_VM_EXEC_CONTROL,
- SECONDARY_EXEC_DESC);
+ if (!boot_cpu_has(X86_FEATURE_UMIP) && vmx_umip_emulated()) {
+ if (cr4 & X86_CR4_UMIP) {
+ vmcs_set_bits(SECONDARY_VM_EXEC_CONTROL,
+ SECONDARY_EXEC_DESC);
+ hw_cr4 &= ~X86_CR4_UMIP;
+ } else if (!is_guest_mode(vcpu) ||
+ !nested_cpu_has2(get_vmcs12(vcpu), SECONDARY_EXEC_DESC))
+ vmcs_clear_bits(SECONDARY_VM_EXEC_CONTROL,
+ SECONDARY_EXEC_DESC);
+ }
if (cr4 & X86_CR4_VMXE) {
/*
I'll test it and send the patch more formally.
Thanks,
Paolo
