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SubjectRe: [PATCH 5/5] KVM: vmx: add support for emulating UMIP
2017-11-13 22:40 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>:
> UMIP can be emulated almost perfectly on Intel processor by enabling
> descriptor-table exits. SMSW does not cause a vmexit and hence it
> cannot be changed into a #GP fault, but all in all it's the most
> "innocuous" of the unprivileged instructions that UMIP blocks.
>
> In fact, Linux is _also_ emulating SMSW instructions on behalf of the
> program that executes them, because some 16-bit programs expect to use
> SMSW to detect vm86 mode, so this is an even smaller issue.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Reviewed-by: Wanpeng Li <wanpeng.li@hotmail.com>

> ---
> arch/x86/kvm/vmx.c | 29 +++++++++++++++++++++++++++--
> 1 file changed, 27 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 6c474c94e154..a257ddc644d1 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -3651,6 +3651,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
> SECONDARY_EXEC_ENABLE_EPT |
> SECONDARY_EXEC_UNRESTRICTED_GUEST |
> SECONDARY_EXEC_PAUSE_LOOP_EXITING |
> + SECONDARY_EXEC_DESC |
> SECONDARY_EXEC_RDTSCP |
> SECONDARY_EXEC_ENABLE_INVPCID |
> SECONDARY_EXEC_APIC_REGISTER_VIRT |
> @@ -4347,6 +4348,14 @@ static int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
> (to_vmx(vcpu)->rmode.vm86_active ?
> KVM_RMODE_VM_CR4_ALWAYS_ON : 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
> + vmcs_clear_bits(SECONDARY_VM_EXEC_CONTROL,
> + SECONDARY_EXEC_DESC);
> +
> if (cr4 & X86_CR4_VMXE) {
> /*
> * To use VMXON (and later other VMX instructions), a guest
> @@ -5296,6 +5305,7 @@ static void vmx_compute_secondary_exec_control(struct vcpu_vmx *vmx)
> struct kvm_vcpu *vcpu = &vmx->vcpu;
>
> u32 exec_control = vmcs_config.cpu_based_2nd_exec_ctrl;
> +
> if (!cpu_need_virtualize_apic_accesses(vcpu))
> exec_control &= ~SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES;
> if (vmx->vpid == 0)
> @@ -5314,6 +5324,11 @@ static void vmx_compute_secondary_exec_control(struct vcpu_vmx *vmx)
> exec_control &= ~(SECONDARY_EXEC_APIC_REGISTER_VIRT |
> SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY);
> exec_control &= ~SECONDARY_EXEC_VIRTUALIZE_X2APIC_MODE;
> +
> + /* SECONDARY_EXEC_DESC is enabled/disabled on writes to CR4.UMIP,
> + * in vmx_set_cr4. */
> + exec_control &= ~SECONDARY_EXEC_DESC;
> +
> /* SECONDARY_EXEC_SHADOW_VMCS is enabled when L1 executes VMPTRLD
> (handle_vmptrld).
> We can NOT enable shadow_vmcs here because we don't have yet
> @@ -6064,6 +6079,12 @@ static int handle_set_cr4(struct kvm_vcpu *vcpu, unsigned long val)
> return kvm_set_cr4(vcpu, val);
> }
>
> +static int handle_desc(struct kvm_vcpu *vcpu)
> +{
> + WARN_ON(!(vcpu->arch.cr4 & X86_CR4_UMIP));
> + return emulate_instruction(vcpu, 0) == EMULATE_DONE;
> +}
> +
> static int handle_cr(struct kvm_vcpu *vcpu)
> {
> unsigned long exit_qualification, val;
> @@ -8152,6 +8173,8 @@ static int (*const kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
> [EXIT_REASON_XSETBV] = handle_xsetbv,
> [EXIT_REASON_TASK_SWITCH] = handle_task_switch,
> [EXIT_REASON_MCE_DURING_VMENTRY] = handle_machine_check,
> + [EXIT_REASON_GDTR_IDTR] = handle_desc,
> + [EXIT_REASON_LDTR_TR] = handle_desc,
> [EXIT_REASON_EPT_VIOLATION] = handle_ept_violation,
> [EXIT_REASON_EPT_MISCONFIG] = handle_ept_misconfig,
> [EXIT_REASON_PAUSE_INSTRUCTION] = handle_pause,
> @@ -9097,7 +9120,8 @@ static bool vmx_xsaves_supported(void)
>
> static bool vmx_umip_emulated(void)
> {
> - return false;
> + return vmcs_config.cpu_based_2nd_exec_ctrl &
> + SECONDARY_EXEC_DESC;
> }
>
> static void vmx_recover_nmi_blocking(struct vcpu_vmx *vmx)
> @@ -9691,7 +9715,8 @@ static void vmcs_set_secondary_exec_control(u32 new_ctl)
> u32 mask =
> SECONDARY_EXEC_SHADOW_VMCS |
> SECONDARY_EXEC_VIRTUALIZE_X2APIC_MODE |
> - SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES;
> + SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES |
> + SECONDARY_EXEC_DESC;
>
> u32 cur_ctl = vmcs_read32(SECONDARY_VM_EXEC_CONTROL);
>
> --
> 1.8.3.1
>

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