linux-kernel - Re: [PATCH 5/5] KVM: vmx: add support for emulating UMIP

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Date:   Wed, 15 Nov 2017 08:42:48 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>, Radim Krcmar <rkrcmar@...hat.com>
Subject: Re: [PATCH 5/5] KVM: vmx: add support for emulating UMIP

2017-11-13 22:40 GMT+08:00 Paolo Bonzini <pbonzini@...hat.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@...hat.com>

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