[v3,2/3] kvm: Add support to KVM_GET_MSR_FEATURE_INDEX_LIST and KVM_GET_MSRS system ioctl

Message ID 1533909989-56115-3-git-send-email-robert.hu@linux.intel.com
State New
Headers show
Series
  • x86: QEMU side support on MSR based features
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Commit Message

Robert Hoo Aug. 10, 2018, 2:06 p.m.
Add kvm_get_supported_feature_msrs() to get supported MSR feature index list.
Add kvm_arch_get_supported_msr_feature() to get each MSR features value.

kvm_get_supported_feature_msrs() is called in kvm_arch_init().
kvm_arch_get_supported_msr_feature() is called by
x86_cpu_get_supported_feature_word().

Signed-off-by: Robert Hoo <robert.hu@linux.intel.com>
---
 include/sysemu/kvm.h |  2 ++
 target/i386/kvm.c    | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 81 insertions(+)

Comments

Eduardo Habkost Aug. 17, 2018, 1:18 p.m. | #1
Thanks for the patch, comments below:

On Fri, Aug 10, 2018 at 10:06:28PM +0800, Robert Hoo wrote:
> Add kvm_get_supported_feature_msrs() to get supported MSR feature index list.
> Add kvm_arch_get_supported_msr_feature() to get each MSR features value.
> 
> kvm_get_supported_feature_msrs() is called in kvm_arch_init().
> kvm_arch_get_supported_msr_feature() is called by
> x86_cpu_get_supported_feature_word().
> 
> Signed-off-by: Robert Hoo <robert.hu@linux.intel.com>
> ---
>  include/sysemu/kvm.h |  2 ++
>  target/i386/kvm.c    | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 81 insertions(+)
> 
> diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
> index 0b64b8e..97d8d9d 100644
> --- a/include/sysemu/kvm.h
> +++ b/include/sysemu/kvm.h
> @@ -463,6 +463,8 @@ int kvm_vm_check_extension(KVMState *s, unsigned int extension);
>  
>  uint32_t kvm_arch_get_supported_cpuid(KVMState *env, uint32_t function,
>                                        uint32_t index, int reg);
> +uint32_t kvm_arch_get_supported_msr_feature(KVMState *s, uint32_t index);
> +
>  
>  void kvm_set_sigmask_len(KVMState *s, unsigned int sigmask_len);
>  
> diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> index 9313602..70d8606 100644
> --- a/target/i386/kvm.c
> +++ b/target/i386/kvm.c
> @@ -107,6 +107,7 @@ static int has_pit_state2;
>  static bool has_msr_mcg_ext_ctl;
>  
>  static struct kvm_cpuid2 *cpuid_cache;
> +static struct kvm_msr_list *kvm_feature_msrs;

I was going to suggest moving this to KVMState, but KVMState is a
arch-independent struct.  I guess we'll have to live with this by
now.

>  
>  int kvm_has_pit_state2(void)
>  {
> @@ -420,6 +421,41 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function,
>      return ret;
>  }
>  
> +uint32_t kvm_arch_get_supported_msr_feature(KVMState *s, uint32_t index)
> +{
> +    struct {
> +        struct kvm_msrs info;
> +        struct kvm_msr_entry entries[1];
> +    } msr_data;
> +    uint32_t ret;
> +
> +    /*Check if the requested feature MSR is supported*/
> +    int i;
> +    for (i = 0; i < kvm_feature_msrs->nmsrs; i++) {
> +        if (index == kvm_feature_msrs->indices[i]) {
> +            break;
> +        }
> +    }

We are duplicating the logic that's already inside KVM (checking
the list of supported MSRs and returning an error).  Can't we
make this simpler and just remove this check?  If the MSR is not
supported, KVM_GET_MSRS would just return 0.

> +    if (i >= kvm_feature_msrs->nmsrs) {
> +        fprintf(stderr, "Requested MSR (index= %d) is not supported.\n", index);

This error message is meaningless for QEMU users.  Do we really
need to print it?

> +        return 0;

Returning 0 for MSRs that are not supported is probably OK, but
we need to see this function being used, to be sure (I didn't
look at all the patches in this series yet).

> +    }
> +
> +    msr_data.info.nmsrs = 1;
> +    msr_data.entries[0].index = index;
> +
> +    ret = kvm_ioctl(s, KVM_GET_MSRS, &msr_data);
> +
> +    if (ret != 1) {
> +        fprintf(stderr, "KVM get MSR (index=0x%x) feature failed, %s\n",
> +            index, strerror(-ret));
> +        exit(1);

I'm not a fan of APIs that write to stdout/stderr or exit(),
unless they are clearly just initialization functions that should
never fail in normal circumstances.

But if you call KVM_GET_MSRS for all MSRs at
kvm_get_supported_feature_msrs() below, this function would never
need to report an error.

We are already going through the trouble of allocating
kvm_feature_msrs in kvm_get_supported_feature_msrs() anyway.

> +    }
> +
> +    return msr_data.entries[0].data;
> +}
> +
> +
>  typedef struct HWPoisonPage {
>      ram_addr_t ram_addr;
>      QLIST_ENTRY(HWPoisonPage) list;
> @@ -1238,7 +1274,45 @@ void kvm_arch_do_init_vcpu(X86CPU *cpu)
>          env->mp_state = KVM_MP_STATE_INIT_RECEIVED;
>      }
>  }

Nit: please add an extra newline between functions.

> +static int kvm_get_supported_feature_msrs(KVMState *s)
> +{
> +    static int kvm_supported_feature_msrs;
> +    int ret = 0;
> +
> +    if (kvm_supported_feature_msrs == 0) {

Do you really need the kvm_supported_feature_msrs variable?  You
could just check if kvm_feature_msrs is NULL.

I also suggest doing this:

    if (already initialized) {
       return 0;
    }

    /* regular initialization code here */

to reduce one indentation level.


> +        struct kvm_msr_list msr_list;
> +
> +        kvm_supported_feature_msrs++;
> +
> +        msr_list.nmsrs = 0;
> +        ret = kvm_ioctl(s, KVM_GET_MSR_FEATURE_INDEX_LIST, &msr_list);
> +        if (ret < 0 && ret != -E2BIG) {
> +            return ret;

What if the host KVM version doesn't support
KVM_GET_MSR_FEATURE_INDEX_LIST?

> +        }
> +
> +        assert(msr_list.nmsrs > 0);
> +        kvm_feature_msrs = (struct kvm_msr_list *) \
> +            g_malloc0(sizeof(msr_list) +
> +                     msr_list.nmsrs * sizeof(msr_list.indices[0]));
> +        if (kvm_feature_msrs == NULL) {

g_malloc0() never returns NULL on failure.  See
https://developer.gnome.org/glib/2.56/glib-Memory-Allocation.html#glib-Memory-Allocation.description

> +            fprintf(stderr, "Failed to allocate space for KVM Feature MSRs"
> +                "which has %d MSRs\n", msr_list.nmsrs);
> +            return -1;
> +        }
> +
> +        kvm_feature_msrs->nmsrs = msr_list.nmsrs;
> +        ret = kvm_ioctl(s, KVM_GET_MSR_FEATURE_INDEX_LIST, kvm_feature_msrs);
>  
> +        if (ret < 0) {  /*ioctl failure*/

Small nit: the "ioctl failure" comment seems unnecessary, I would
just remove it.

> +            fprintf(stderr, "Fetch KVM feature MSRs failed: %s\n",
> +                strerror(-ret));
> +            g_free(kvm_feature_msrs);
> +            return ret;
> +        }
> +    }
> +
> +    return 0;
> +}

Same as above: please add an extra newline between functions.

>  static int kvm_get_supported_msrs(KVMState *s)
>  {
>      static int kvm_supported_msrs;
> @@ -1400,6 +1474,11 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>          return ret;
>      }
>  
> +    ret = kvm_get_supported_feature_msrs(s);
> +    if (ret < 0) {
> +        return ret;
> +    }
> +
>      uname(&utsname);
>      lm_capable_kernel = strcmp(utsname.machine, "x86_64") == 0;
>  
> -- 
> 1.8.3.1
> 
>
Robert Hoo Aug. 18, 2018, 7:27 a.m. | #2
On Fri, 2018-08-17 at 10:18 -0300, Eduardo Habkost wrote:
> Thanks for the patch, comments below:
> 
> On Fri, Aug 10, 2018 at 10:06:28PM +0800, Robert Hoo wrote:
> > Add kvm_get_supported_feature_msrs() to get supported MSR feature index list.
> > Add kvm_arch_get_supported_msr_feature() to get each MSR features value.
> > 
> > kvm_get_supported_feature_msrs() is called in kvm_arch_init().
> > kvm_arch_get_supported_msr_feature() is called by
> > x86_cpu_get_supported_feature_word().
> > 
> > Signed-off-by: Robert Hoo <robert.hu@linux.intel.com>
> > ---
> >  include/sysemu/kvm.h |  2 ++
> >  target/i386/kvm.c    | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 81 insertions(+)
> > 
> > diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
> > index 0b64b8e..97d8d9d 100644
> > --- a/include/sysemu/kvm.h
> > +++ b/include/sysemu/kvm.h
> > @@ -463,6 +463,8 @@ int kvm_vm_check_extension(KVMState *s, unsigned int extension);
> >  
> >  uint32_t kvm_arch_get_supported_cpuid(KVMState *env, uint32_t function,
> >                                        uint32_t index, int reg);
> > +uint32_t kvm_arch_get_supported_msr_feature(KVMState *s, uint32_t index);
> > +
> >  
> >  void kvm_set_sigmask_len(KVMState *s, unsigned int sigmask_len);
> >  
> > diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> > index 9313602..70d8606 100644
> > --- a/target/i386/kvm.c
> > +++ b/target/i386/kvm.c
> > @@ -107,6 +107,7 @@ static int has_pit_state2;
> >  static bool has_msr_mcg_ext_ctl;
> >  
> >  static struct kvm_cpuid2 *cpuid_cache;
> > +static struct kvm_msr_list *kvm_feature_msrs;
> 
> I was going to suggest moving this to KVMState, but KVMState is a
> arch-independent struct.  I guess we'll have to live with this by
> now.
> 
> >  
> >  int kvm_has_pit_state2(void)
> >  {
> > @@ -420,6 +421,41 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function,
> >      return ret;
> >  }
> >  
> > +uint32_t kvm_arch_get_supported_msr_feature(KVMState *s, uint32_t index)
> > +{
> > +    struct {
> > +        struct kvm_msrs info;
> > +        struct kvm_msr_entry entries[1];
> > +    } msr_data;
> > +    uint32_t ret;
> > +
> > +    /*Check if the requested feature MSR is supported*/
> > +    int i;
> > +    for (i = 0; i < kvm_feature_msrs->nmsrs; i++) {
> > +        if (index == kvm_feature_msrs->indices[i]) {
> > +            break;
> > +        }
> > +    }
> 
> We are duplicating the logic that's already inside KVM (checking
> the list of supported MSRs and returning an error).  Can't we
> make this simpler and just remove this check?  If the MSR is not
> supported, KVM_GET_MSRS would just return 0.

Yes, seems dup. but if we remove this hunk, the
kvm_get_supported_feature_msrs() is unnecessary at all.
> 
> > +    if (i >= kvm_feature_msrs->nmsrs) {
> > +        fprintf(stderr, "Requested MSR (index= %d) is not supported.\n", index);
> 
> This error message is meaningless for QEMU users.  Do we really
> need to print it?
> 
> > +        return 0;
> 
> Returning 0 for MSRs that are not supported is probably OK, but
> we need to see this function being used, to be sure (I didn't
> look at all the patches in this series yet).
> 
> > +    }
> > +
> > +    msr_data.info.nmsrs = 1;
> > +    msr_data.entries[0].index = index;
> > +
> > +    ret = kvm_ioctl(s, KVM_GET_MSRS, &msr_data);
> > +
> > +    if (ret != 1) {
> > +        fprintf(stderr, "KVM get MSR (index=0x%x) feature failed, %s\n",
> > +            index, strerror(-ret));
> > +        exit(1);
> 
> I'm not a fan of APIs that write to stdout/stderr or exit(),
> unless they are clearly just initialization functions that should
> never fail in normal circumstances.
> 
> But if you call KVM_GET_MSRS for all MSRs at
> kvm_get_supported_feature_msrs() below, this function would never
> need to report an error.
> 
> We are already going through the trouble of allocating
> kvm_feature_msrs in kvm_get_supported_feature_msrs() anyway.

I had looked into KVM KVM_GET_MSRS handling, though less likely, still
have changes copy_from/to_user() fail. Therefore I added the check and
warning here, in that seldom case happens.

exit() or not, I'm also not sure. Seems not necessary, while my usual
programming philosophy is never let wrong goes further. For in the case
of ioctl(KVM_GET_MSRS) returns failure, something goes wrong underlying,
I would prefer to let user know this, rather than let it pass and goes
further.
> 
> > +    }
> > +
> > +    return msr_data.entries[0].data;
> > +}
> > +
> > +
> >  typedef struct HWPoisonPage {
> >      ram_addr_t ram_addr;
> >      QLIST_ENTRY(HWPoisonPage) list;
> > @@ -1238,7 +1274,45 @@ void kvm_arch_do_init_vcpu(X86CPU *cpu)
> >          env->mp_state = KVM_MP_STATE_INIT_RECEIVED;
> >      }
> >  }
> 
> Nit: please add an extra newline between functions.
> 
> > +static int kvm_get_supported_feature_msrs(KVMState *s)
> > +{
> > +    static int kvm_supported_feature_msrs;
> > +    int ret = 0;
> > +
> > +    if (kvm_supported_feature_msrs == 0) {
> 
> Do you really need the kvm_supported_feature_msrs variable?  You
> could just check if kvm_feature_msrs is NULL.
> 
> I also suggest doing this:
> 
>     if (already initialized) {
>        return 0;
>     }
> 
>     /* regular initialization code here */
> 
> to reduce one indentation level.
> 
Right.
> 
> > +        struct kvm_msr_list msr_list;
> > +
> > +        kvm_supported_feature_msrs++;
> > +
> > +        msr_list.nmsrs = 0;
> > +        ret = kvm_ioctl(s, KVM_GET_MSR_FEATURE_INDEX_LIST, &msr_list);
> > +        if (ret < 0 && ret != -E2BIG) {
> > +            return ret;
> 
> What if the host KVM version doesn't support
> KVM_GET_MSR_FEATURE_INDEX_LIST?

Going to add kvm_check_extension(s, KVM_CAP_GET_MSR_FEATURES) before
this ioctl. if not support, return -1. (Then the kvm_init will fail and
exit.)
> 
> > +        }
> > +
> > +        assert(msr_list.nmsrs > 0);
> > +        kvm_feature_msrs = (struct kvm_msr_list *) \
> > +            g_malloc0(sizeof(msr_list) +
> > +                     msr_list.nmsrs * sizeof(msr_list.indices[0]));
> > +        if (kvm_feature_msrs == NULL) {
> 
> g_malloc0() never returns NULL on failure.  See
> https://developer.gnome.org/glib/2.56/glib-Memory-Allocation.html#glib-Memory-Allocation.description
> 
Thanks!

> > +            fprintf(stderr, "Failed to allocate space for KVM Feature MSRs"
> > +                "which has %d MSRs\n", msr_list.nmsrs);
> > +            return -1;
> > +        }
> > +
> > +        kvm_feature_msrs->nmsrs = msr_list.nmsrs;
> > +        ret = kvm_ioctl(s, KVM_GET_MSR_FEATURE_INDEX_LIST, kvm_feature_msrs);
> >  
> > +        if (ret < 0) {  /*ioctl failure*/
> 
> Small nit: the "ioctl failure" comment seems unnecessary, I would
> just remove it.
> 
> > +            fprintf(stderr, "Fetch KVM feature MSRs failed: %s\n",
> > +                strerror(-ret));
> > +            g_free(kvm_feature_msrs);
> > +            return ret;
> > +        }
> > +    }
> > +
> > +    return 0;
> > +}
> 
> Same as above: please add an extra newline between functions.
> 
> >  static int kvm_get_supported_msrs(KVMState *s)
> >  {
> >      static int kvm_supported_msrs;
> > @@ -1400,6 +1474,11 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
> >          return ret;
> >      }
> >  
> > +    ret = kvm_get_supported_feature_msrs(s);
> > +    if (ret < 0) {
> > +        return ret;
> > +    }
> > +
> >      uname(&utsname);
> >      lm_capable_kernel = strcmp(utsname.machine, "x86_64") == 0;
> >  
> > -- 
> > 1.8.3.1
> > 
> > 
>
Eduardo Habkost Aug. 18, 2018, 3:05 p.m. | #3
On Sat, Aug 18, 2018 at 03:27:01PM +0800, Robert Hoo wrote:
> On Fri, 2018-08-17 at 10:18 -0300, Eduardo Habkost wrote:
> > Thanks for the patch, comments below:
> > 
> > On Fri, Aug 10, 2018 at 10:06:28PM +0800, Robert Hoo wrote:
> > > Add kvm_get_supported_feature_msrs() to get supported MSR feature index list.
> > > Add kvm_arch_get_supported_msr_feature() to get each MSR features value.
> > > 
> > > kvm_get_supported_feature_msrs() is called in kvm_arch_init().
> > > kvm_arch_get_supported_msr_feature() is called by
> > > x86_cpu_get_supported_feature_word().
> > > 
> > > Signed-off-by: Robert Hoo <robert.hu@linux.intel.com>
> > > ---
> > >  include/sysemu/kvm.h |  2 ++
> > >  target/i386/kvm.c    | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> > >  2 files changed, 81 insertions(+)
> > > 
> > > diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
> > > index 0b64b8e..97d8d9d 100644
> > > --- a/include/sysemu/kvm.h
> > > +++ b/include/sysemu/kvm.h
> > > @@ -463,6 +463,8 @@ int kvm_vm_check_extension(KVMState *s, unsigned int extension);
> > >  
> > >  uint32_t kvm_arch_get_supported_cpuid(KVMState *env, uint32_t function,
> > >                                        uint32_t index, int reg);
> > > +uint32_t kvm_arch_get_supported_msr_feature(KVMState *s, uint32_t index);
> > > +
> > >  
> > >  void kvm_set_sigmask_len(KVMState *s, unsigned int sigmask_len);
> > >  
> > > diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> > > index 9313602..70d8606 100644
> > > --- a/target/i386/kvm.c
> > > +++ b/target/i386/kvm.c
> > > @@ -107,6 +107,7 @@ static int has_pit_state2;
> > >  static bool has_msr_mcg_ext_ctl;
> > >  
> > >  static struct kvm_cpuid2 *cpuid_cache;
> > > +static struct kvm_msr_list *kvm_feature_msrs;
> > 
> > I was going to suggest moving this to KVMState, but KVMState is a
> > arch-independent struct.  I guess we'll have to live with this by
> > now.
> > 
> > >  
> > >  int kvm_has_pit_state2(void)
> > >  {
> > > @@ -420,6 +421,41 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function,
> > >      return ret;
> > >  }
> > >  
> > > +uint32_t kvm_arch_get_supported_msr_feature(KVMState *s, uint32_t index)
> > > +{
> > > +    struct {
> > > +        struct kvm_msrs info;
> > > +        struct kvm_msr_entry entries[1];
> > > +    } msr_data;
> > > +    uint32_t ret;
> > > +
> > > +    /*Check if the requested feature MSR is supported*/
> > > +    int i;
> > > +    for (i = 0; i < kvm_feature_msrs->nmsrs; i++) {
> > > +        if (index == kvm_feature_msrs->indices[i]) {
> > > +            break;
> > > +        }
> > > +    }
> > 
> > We are duplicating the logic that's already inside KVM (checking
> > the list of supported MSRs and returning an error).  Can't we
> > make this simpler and just remove this check?  If the MSR is not
> > supported, KVM_GET_MSRS would just return 0.
> 
> Yes, seems dup. but if we remove this hunk, the
> kvm_get_supported_feature_msrs() is unnecessary at all.

So maybe kvm_get_supported_feature_msrs() really is unnecessary?

We seem to have two alternatives:
* calling KVM_GET_MSRS for all MSRs only once, at
  kvm_get_supported_feature_msrs() (as I had suggested
  previously);
* calling KVM_GET_MSRS for one MSR unconditionally here, but
  _not_ treating 0 as a fatal error.

I prefer the former, but I would be OK with both alternatives.
Note that we need to check for KVM capabilities in both cases.


> > 
> > > +    if (i >= kvm_feature_msrs->nmsrs) {
> > > +        fprintf(stderr, "Requested MSR (index= %d) is not supported.\n", index);
> > 
> > This error message is meaningless for QEMU users.  Do we really
> > need to print it?
> > 
> > > +        return 0;
> > 
> > Returning 0 for MSRs that are not supported is probably OK, but
> > we need to see this function being used, to be sure (I didn't
> > look at all the patches in this series yet).
> > 
> > > +    }
> > > +
> > > +    msr_data.info.nmsrs = 1;
> > > +    msr_data.entries[0].index = index;
> > > +
> > > +    ret = kvm_ioctl(s, KVM_GET_MSRS, &msr_data);
> > > +
> > > +    if (ret != 1) {
> > > +        fprintf(stderr, "KVM get MSR (index=0x%x) feature failed, %s\n",
> > > +            index, strerror(-ret));
> > > +        exit(1);
> > 
> > I'm not a fan of APIs that write to stdout/stderr or exit(),
> > unless they are clearly just initialization functions that should
> > never fail in normal circumstances.
> > 
> > But if you call KVM_GET_MSRS for all MSRs at
> > kvm_get_supported_feature_msrs() below, this function would never
> > need to report an error.
> > 
> > We are already going through the trouble of allocating
> > kvm_feature_msrs in kvm_get_supported_feature_msrs() anyway.
> 
> I had looked into KVM KVM_GET_MSRS handling, though less likely, still
> have changes copy_from/to_user() fail. Therefore I added the check and
> warning here, in that seldom case happens.
> 
> exit() or not, I'm also not sure. Seems not necessary, while my usual
> programming philosophy is never let wrong goes further. For in the case
> of ioctl(KVM_GET_MSRS) returns failure, something goes wrong underlying,
> I would prefer to let user know this, rather than let it pass and goes
> further.

We probably have no option other than exiting if KVM_GET_MSRS
returns an unexpected error.  It's just that I find the code
harder to review, because we need to be sure this won't terminate
QEMU under normal circumstances.

But if you demonstrate that all errors here are truly fatal and
unexpected, calling exit() may be OK.  (See the
KVM_CAP_GET_MSR_FEATURES comment below for one example where
exiting is not going to be OK.)

Proper error reporting using Error** would be even better than
exiting, but considering that none of the functions at i386/cpu.c
return errors using Error**, I won't force you to do that.


> > 
[...]
> > > +        struct kvm_msr_list msr_list;
> > > +
> > > +        kvm_supported_feature_msrs++;
> > > +
> > > +        msr_list.nmsrs = 0;
> > > +        ret = kvm_ioctl(s, KVM_GET_MSR_FEATURE_INDEX_LIST, &msr_list);
> > > +        if (ret < 0 && ret != -E2BIG) {
> > > +            return ret;
> > 
> > What if the host KVM version doesn't support
> > KVM_GET_MSR_FEATURE_INDEX_LIST?
> 
> Going to add kvm_check_extension(s, KVM_CAP_GET_MSR_FEATURES) before
> this ioctl. if not support, return -1. (Then the kvm_init will fail and
> exit.)

We don't want QEMU to refuse to run if the kernel doesn't have
KVM_CAP_GET_MSR_FEATURES.  We can treat missing capability as
equivalent to returning an empty list of MSRs.

Patch

diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
index 0b64b8e..97d8d9d 100644
--- a/include/sysemu/kvm.h
+++ b/include/sysemu/kvm.h
@@ -463,6 +463,8 @@  int kvm_vm_check_extension(KVMState *s, unsigned int extension);
 
 uint32_t kvm_arch_get_supported_cpuid(KVMState *env, uint32_t function,
                                       uint32_t index, int reg);
+uint32_t kvm_arch_get_supported_msr_feature(KVMState *s, uint32_t index);
+
 
 void kvm_set_sigmask_len(KVMState *s, unsigned int sigmask_len);
 
diff --git a/target/i386/kvm.c b/target/i386/kvm.c
index 9313602..70d8606 100644
--- a/target/i386/kvm.c
+++ b/target/i386/kvm.c
@@ -107,6 +107,7 @@  static int has_pit_state2;
 static bool has_msr_mcg_ext_ctl;
 
 static struct kvm_cpuid2 *cpuid_cache;
+static struct kvm_msr_list *kvm_feature_msrs;
 
 int kvm_has_pit_state2(void)
 {
@@ -420,6 +421,41 @@  uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function,
     return ret;
 }
 
+uint32_t kvm_arch_get_supported_msr_feature(KVMState *s, uint32_t index)
+{
+    struct {
+        struct kvm_msrs info;
+        struct kvm_msr_entry entries[1];
+    } msr_data;
+    uint32_t ret;
+
+    /*Check if the requested feature MSR is supported*/
+    int i;
+    for (i = 0; i < kvm_feature_msrs->nmsrs; i++) {
+        if (index == kvm_feature_msrs->indices[i]) {
+            break;
+        }
+    }
+    if (i >= kvm_feature_msrs->nmsrs) {
+        fprintf(stderr, "Requested MSR (index= %d) is not supported.\n", index);
+        return 0;
+    }
+
+    msr_data.info.nmsrs = 1;
+    msr_data.entries[0].index = index;
+
+    ret = kvm_ioctl(s, KVM_GET_MSRS, &msr_data);
+
+    if (ret != 1) {
+        fprintf(stderr, "KVM get MSR (index=0x%x) feature failed, %s\n",
+            index, strerror(-ret));
+        exit(1);
+    }
+
+    return msr_data.entries[0].data;
+}
+
+
 typedef struct HWPoisonPage {
     ram_addr_t ram_addr;
     QLIST_ENTRY(HWPoisonPage) list;
@@ -1238,7 +1274,45 @@  void kvm_arch_do_init_vcpu(X86CPU *cpu)
         env->mp_state = KVM_MP_STATE_INIT_RECEIVED;
     }
 }
+static int kvm_get_supported_feature_msrs(KVMState *s)
+{
+    static int kvm_supported_feature_msrs;
+    int ret = 0;
+
+    if (kvm_supported_feature_msrs == 0) {
+        struct kvm_msr_list msr_list;
+
+        kvm_supported_feature_msrs++;
+
+        msr_list.nmsrs = 0;
+        ret = kvm_ioctl(s, KVM_GET_MSR_FEATURE_INDEX_LIST, &msr_list);
+        if (ret < 0 && ret != -E2BIG) {
+            return ret;
+        }
+
+        assert(msr_list.nmsrs > 0);
+        kvm_feature_msrs = (struct kvm_msr_list *) \
+            g_malloc0(sizeof(msr_list) +
+                     msr_list.nmsrs * sizeof(msr_list.indices[0]));
+        if (kvm_feature_msrs == NULL) {
+            fprintf(stderr, "Failed to allocate space for KVM Feature MSRs"
+                "which has %d MSRs\n", msr_list.nmsrs);
+            return -1;
+        }
+
+        kvm_feature_msrs->nmsrs = msr_list.nmsrs;
+        ret = kvm_ioctl(s, KVM_GET_MSR_FEATURE_INDEX_LIST, kvm_feature_msrs);
 
+        if (ret < 0) {  /*ioctl failure*/
+            fprintf(stderr, "Fetch KVM feature MSRs failed: %s\n",
+                strerror(-ret));
+            g_free(kvm_feature_msrs);
+            return ret;
+        }
+    }
+
+    return 0;
+}
 static int kvm_get_supported_msrs(KVMState *s)
 {
     static int kvm_supported_msrs;
@@ -1400,6 +1474,11 @@  int kvm_arch_init(MachineState *ms, KVMState *s)
         return ret;
     }
 
+    ret = kvm_get_supported_feature_msrs(s);
+    if (ret < 0) {
+        return ret;
+    }
+
     uname(&utsname);
     lm_capable_kernel = strcmp(utsname.machine, "x86_64") == 0;