Re: [Qemu-devel] [PATCH 1/5] i386: Add support for IA32_PRED_CMD and IA32_ARCH_CAPABILITIES MSRs

[Paolo Bonzini]

On 25/06/2018 05:39, Robert Hoo wrote:
> IA32_PRED_CMD MSR gives software a way to issue commands that affect the state
> of indirect branch predictors. Enumerated by CPUID.(EAX=7H,ECX=0):EDX[26].
> IA32_ARCH_CAPABILITIES MSR enumerates architectural features of RDCL_NO and
> IBRS_ALL. Enumerated by CPUID.(EAX=07H, ECX=0):EDX[29].
> 
> https://software.intel.com/sites/default/files/managed/c5/63/336996-Speculative-Execution-Side-Channel-Mitigations.pdf
> 
> Signed-off-by: Robert Hoo <address@hidden>
> ---
>  target/i386/cpu.h     |  4 ++++
>  target/i386/kvm.c     | 27 ++++++++++++++++++++++++++-
>  target/i386/machine.c | 40 ++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 70 insertions(+), 1 deletion(-)
> 
> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> index 89c82be..734a73e 100644
> --- a/target/i386/cpu.h
> +++ b/target/i386/cpu.h
> @@ -352,6 +352,8 @@ typedef enum X86Seg {
>  #define MSR_TSC_ADJUST                  0x0000003b
>  #define MSR_IA32_SPEC_CTRL              0x48
>  #define MSR_VIRT_SSBD                   0xc001011f
> +#define MSR_IA32_PRED_CMD               0x49
> +#define MSR_IA32_ARCH_CAPABILITIES      0x10a
>  #define MSR_IA32_TSCDEADLINE            0x6e0
>  
>  #define FEATURE_CONTROL_LOCKED                    (1<<0)
> @@ -1210,6 +1212,8 @@ typedef struct CPUX86State {
>  
>      uint64_t spec_ctrl;
>      uint64_t virt_ssbd;
> +    uint64_t pred_cmd;
> +    uint64_t arch_capabilities;
>  
>      /* End of state preserved by INIT (dummy marker).  */
>      struct {} end_init_save;
> diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> index 445e0e0..5232446 100644
> --- a/target/i386/kvm.c
> +++ b/target/i386/kvm.c
> @@ -93,6 +93,8 @@ static bool has_msr_hv_reenlightenment;
>  static bool has_msr_xss;
>  static bool has_msr_spec_ctrl;
>  static bool has_msr_virt_ssbd;
> +static bool has_msr_pred_cmd;
> +static bool has_msr_arch_capabilities;
>  static bool has_msr_smi_count;
>  
>  static uint32_t has_architectural_pmu_version;
> @@ -1258,6 +1260,11 @@ static int kvm_get_supported_msrs(KVMState *s)
>                      break;
>                  case MSR_VIRT_SSBD:
>                      has_msr_virt_ssbd = true;
> +                case MSR_IA32_PRED_CMD:
> +                    has_msr_pred_cmd = true;
> +                    break;
> +                case MSR_IA32_ARCH_CAPABILITIES:
> +                    has_msr_arch_capabilities = true;
>                      break;
>                  }
>              }
> @@ -1750,7 +1757,13 @@ static int kvm_put_msrs(X86CPU *cpu, int level)
>      if (has_msr_virt_ssbd) {
>          kvm_msr_entry_add(cpu, MSR_VIRT_SSBD, env->virt_ssbd);
>      }
> -
> +    if (has_msr_pred_cmd) {
> +        kvm_msr_entry_add(cpu, MSR_IA32_PRED_CMD, env->pred_cmd);
> +    }
> +    if (has_msr_arch_capabilities) {
> +        kvm_msr_entry_add(cpu, MSR_IA32_ARCH_CAPABILITIES,
> +            env->arch_capabilities);
> +    }
>  #ifdef TARGET_X86_64
>      if (lm_capable_kernel) {
>          kvm_msr_entry_add(cpu, MSR_CSTAR, env->cstar);
> @@ -2133,6 +2146,13 @@ static int kvm_get_msrs(X86CPU *cpu)
>      if (has_msr_virt_ssbd) {
>          kvm_msr_entry_add(cpu, MSR_VIRT_SSBD, 0);
>      }
> +    if (has_msr_pred_cmd) {
> +        kvm_msr_entry_add(cpu, MSR_IA32_PRED_CMD, 0);
> +    }
> +    if (has_msr_arch_capabilities) {
> +        kvm_msr_entry_add(cpu, MSR_IA32_ARCH_CAPABILITIES, 0);
> +    }
> +
>      if (!env->tsc_valid) {
>          kvm_msr_entry_add(cpu, MSR_IA32_TSC, 0);
>          env->tsc_valid = !runstate_is_running();
> @@ -2514,6 +2534,11 @@ static int kvm_get_msrs(X86CPU *cpu)
>              break;
>          case MSR_VIRT_SSBD:
>              env->virt_ssbd = msrs[i].data;
> +        case MSR_IA32_PRED_CMD:
> +            env->pred_cmd = msrs[i].data;
> +            break;
> +        case MSR_IA32_ARCH_CAPABILITIES:
> +            env->arch_capabilities = msrs[i].data;
>              break;
>          case MSR_IA32_RTIT_CTL:
>              env->msr_rtit_ctrl = msrs[i].data;
> diff --git a/target/i386/machine.c b/target/i386/machine.c
> index 4d98d36..089aba0 100644
> --- a/target/i386/machine.c
> +++ b/target/i386/machine.c
> @@ -879,6 +879,44 @@ static const VMStateDescription vmstate_spec_ctrl = {
>      }
>  };
>  
> +static bool pred_cmd_needed(void *opaque)
> +{
> +    X86CPU *cpu = opaque;
> +    CPUX86State *env = &cpu->env;
> +
> +    return env->pred_cmd != 0;
> +}
> +
> +static const VMStateDescription vmstate_pred_cmd = {
> +    .name = "cpu/pred_cmd",
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .needed = pred_cmd_needed,
> +    .fields = (VMStateField[]){
> +        VMSTATE_UINT64(env.arch_capabilities, X86CPU),
> +        VMSTATE_END_OF_LIST()
> +    }
> +};
> +
> +static bool arch_capabilities_needed(void *opaque)
> +{
> +    X86CPU *cpu = opaque;
> +    CPUX86State *env = &cpu->env;
> +
> +    return env->arch_capabilities != 0;
> +}
> +
> +static const VMStateDescription vmstate_arch_capabilities = {
> +    .name = "cpu/arch_capabilities",
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .needed = arch_capabilities_needed,
> +    .fields = (VMStateField[]){
> +        VMSTATE_UINT64(env.arch_capabilities, X86CPU),
> +        VMSTATE_END_OF_LIST()
> +    }
> +};
> +
>  static bool intel_pt_enable_needed(void *opaque)
>  {
>      X86CPU *cpu = opaque;
> @@ -1056,6 +1094,8 @@ VMStateDescription vmstate_x86_cpu = {
>          &vmstate_pkru,
>  #endif
>          &vmstate_spec_ctrl,
> +        &vmstate_pred_cmd,
> +        &vmstate_arch_capabilities,
>          &vmstate_mcg_ext_ctl,
>          &vmstate_msr_intel_pt,
>          &vmstate_msr_virt_ssbd,
> 

This is not needed, because pred_cmd is write only and arch_capabilities
is read only.  The guest cannot modify any of them.

Paolo