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

[Robert Hoo]

On Mon, 2018-06-25 at 13:51 +0200, Paolo Bonzini wrote:
> 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.
> 
Thanks Paolo. Yes, indeed unnecessary.
I looked into the
336996-Speculative-Execution-Side-Channel-Mitigations.pdf again, looks
like the vmstate_spec_ctrl is similar to pred_cmd, wirte only. Shall I
remove it as well in v2 patch?
> Paolo