Re: [PATCH 3/8][KVM VMX]: Add a function to check reserved bits in MSR_CORE_PERF_GLOBAL_CTRL

[Jim Mattson <jmattson@google.com>]

On Mon, May 13, 2019 at 11:57 AM Sean Christopherson
<sean.j.christopherson@intel.com> wrote:
>
> On Wed, Apr 24, 2019 at 07:17:19PM -0400, Krish Sadhukhan wrote:
> > Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
> > Reviewed-by: Karl Heubaum <karl.heubaum@oracle.com>
> > ---
> >  arch/x86/include/asm/kvm_host.h  |  1 +
> >  arch/x86/include/asm/msr-index.h |  7 +++++++
> >  arch/x86/kvm/x86.c               | 20 ++++++++++++++++++++
> >  3 files changed, 28 insertions(+)
> >
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index 4660ce90de7f..c5b3c63129a6 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -1311,6 +1311,7 @@ int kvm_emulate_instruction_from_buffer(struct kvm_vcpu *vcpu,
> >
> >  void kvm_enable_efer_bits(u64);
> >  bool kvm_valid_efer(struct kvm_vcpu *vcpu, u64 efer);
> > +bool kvm_valid_perf_global_ctrl(u64 perf_global);
> >  int kvm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr);
> >  int kvm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr);
> >
> > diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
> > index 8e40c2446fd1..d10e8d4b2842 100644
> > --- a/arch/x86/include/asm/msr-index.h
> > +++ b/arch/x86/include/asm/msr-index.h
> > @@ -775,6 +775,13 @@
> >  #define MSR_CORE_PERF_GLOBAL_CTRL    0x0000038f
> >  #define MSR_CORE_PERF_GLOBAL_OVF_CTRL        0x00000390
> >
> > +/* MSR_CORE_PERF_GLOBAL_CTRL bits */
> > +#define      PERF_GLOBAL_CTRL_PMC0_ENABLE    (1ull << 0)
>
> BIT and BIT_ULL
>
> > +#define      PERF_GLOBAL_CTRL_PMC1_ENABLE    (1ull << 1)
> > +#define      PERF_GLOBAL_CTRL_FIXED0_ENABLE  (1ull << 32)
> > +#define      PERF_GLOBAL_CTRL_FIXED1_ENABLE  (1ull << 33)
> > +#define      PERF_GLOBAL_CTRL_FIXED2_ENABLE  (1ull << 34)
> > +
> >  /* Geode defined MSRs */
> >  #define MSR_GEODE_BUSCONT_CONF0              0x00001900
> >
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 02c8e095a239..ecddb8baaa7f 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -89,8 +89,19 @@ EXPORT_SYMBOL_GPL(kvm_mce_cap_supported);
> >  #ifdef CONFIG_X86_64
> >  static
> >  u64 __read_mostly efer_reserved_bits = ~((u64)(EFER_SCE | EFER_LME | EFER_LMA));
> > +static
> > +u64 __read_mostly perf_global_ctrl_reserved_bits =
> > +                             ~((u64)(PERF_GLOBAL_CTRL_PMC0_ENABLE    |
> > +                                     PERF_GLOBAL_CTRL_PMC1_ENABLE    |
> > +                                     PERF_GLOBAL_CTRL_FIXED0_ENABLE  |
> > +                                     PERF_GLOBAL_CTRL_FIXED1_ENABLE  |
> > +                                     PERF_GLOBAL_CTRL_FIXED2_ENABLE));
> >  #else
> >  static u64 __read_mostly efer_reserved_bits = ~((u64)EFER_SCE);
> > +static
>
> Why is static on a different line?
>
> > +u64 __read_mostly perf_global_ctrl_reserved_bits =
> > +                             ~((u64)(PERF_GLOBAL_CTRL_PMC0_ENABLE    |
> > +                                     PERF_GLOBAL_CTRL_PMC1_ENABLE));
>
> Why are the fixed bits reserved on a 32-bit build?
>
> >  #endif
> >
> >  #define VM_STAT(x) offsetof(struct kvm, stat.x), KVM_STAT_VM
> > @@ -1255,6 +1266,15 @@ static int do_get_msr_feature(struct kvm_vcpu *vcpu, unsigned index, u64 *data)
> >       return 0;
> >  }
> >
> > +bool kvm_valid_perf_global_ctrl(u64 perf_global)
> > +{
> > +     if (perf_global & perf_global_ctrl_reserved_bits)
>
> If the check were correct, this could be:
>
>         return !(perf_blobal & perf_global_ctrl_reserved_bits);
>
> But the check isn't correct, the number of counters is variable, i.e. the
> helper should query the guest's CPUID 0xA (ignoring for the moment the
> fact that this bypasses the PMU handling of guest vs. host ownership).

Aren't the reserved bits already easily calculated as
~pmu->global_ctrl_mask? Well, there's also bit 48, potentially, I
guess, but I don't think kvm virtualizes it.

Once we have this concept, shouldn't intel_pmu_set_msr() return
non-zero if an attempt is made to set a reserved bit of this MSR?

> > +             return false;
> > +
> > +     return true;
> > +}
> > +EXPORT_SYMBOL_GPL(kvm_valid_perf_global_ctrl);
> > +
> >  bool kvm_valid_efer(struct kvm_vcpu *vcpu, u64 efer)
> >  {
> >       if (efer & efer_reserved_bits)
> > --
> > 2.17.2
> >