Re: [PATCH v6 2/2] KVM: x86/xen: update Xen CPUID Leaf 4 (tsc info) sub-leaves, if present

[David Woodhouse]

On Tue, 2022-12-20 at 13:40 +0000, Paul Durrant wrote:
> The scaling information in subleaf 1 should match the values set by KVM in
> the 'vcpu_info' sub-structure 'time_info' (a.k.a. pvclock_vcpu_time_info)
> which is shared with the guest, but is not directly available to the VMM.
> The offset values are not set since a TSC offset is already applied.
> The TSC frequency should also be set in sub-leaf 2.
> 
> Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx>

Reviewed-by: David Woodhouse <dwmw@xxxxxxxxxxxx>

> ---
> Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
> 
> v6:
>  - Stash Xen cpuid base and limit values when cpuid is set
>  - Re-name kvm_xen_setup_tsc_info() to kvm_xen_update_tsc_info()
> 
> v5:
>  - Drop the caching of the CPUID entry pointers and only update the
>    sub-leaves if the CPU frequency has actually changed
> 
> v4:
>  - Update commit comment
> 
> v3:
>  - Add leaf limit check in kvm_xen_set_cpuid()
> 
> v2:
>  - Make sure sub-leaf pointers are NULLed if the time leaf is removed
> ---
>  arch/x86/include/asm/kvm_host.h | 11 ++++++-----
>  arch/x86/kvm/cpuid.c            |  2 ++
>  arch/x86/kvm/x86.c              |  1 +
>  arch/x86/kvm/xen.c              | 26 ++++++++++++++++++++++++++
>  arch/x86/kvm/xen.h              |  7 +++++++
>  5 files changed, 42 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index ff201ad35551..44329594bdf7 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -678,6 +678,11 @@ struct kvm_vcpu_hv {
>         } nested;
>  };
>  
> +struct kvm_hypervisor_cpuid {
> +       u32 base;
> +       u32 limit;
> +};
> +
>  /* Xen HVM per vcpu emulation context */
>  struct kvm_vcpu_xen {
>         u64 hypercall_rip;
> @@ -698,6 +703,7 @@ struct kvm_vcpu_xen {
>         struct hrtimer timer;
>         int poll_evtchn;
>         struct timer_list poll_timer;
> +       struct kvm_hypervisor_cpuid cpuid;
>  };
>  
>  struct kvm_queued_exception {
> @@ -710,11 +716,6 @@ struct kvm_queued_exception {
>         bool has_payload;
>  };
>  
> -struct kvm_hypervisor_cpuid {
> -       u32 base;
> -       u32 limit;
> -};
> -
>  struct kvm_vcpu_arch {
>         /*
>          * rip and regs accesses must go through
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 2468720f8d84..e661413ddf8d 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -25,6 +25,7 @@
>  #include "mmu.h"
>  #include "trace.h"
>  #include "pmu.h"
> +#include "xen.h"
>  
>  /*
>   * Unlike "struct cpuinfo_x86.x86_capability", kvm_cpu_caps doesn't need to be
> @@ -441,6 +442,7 @@ static int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2,
>         vcpu->arch.cpuid_nent = nent;
>  
>         kvm_update_hypervisor_cpuid(vcpu, KVM_SIGNATURE, &vcpu->arch.kvm_cpuid);
> +       kvm_update_hypervisor_cpuid(vcpu, XEN_SIGNATURE, &vcpu->arch.xen.cpuid);
>         kvm_vcpu_after_set_cpuid(vcpu);
>  
>         return 0;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index fd6c01a39312..60acc55f0c00 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3158,6 +3158,7 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
>                                    &vcpu->hv_clock.tsc_shift,
>                                    &vcpu->hv_clock.tsc_to_system_mul);
>                 vcpu->hw_tsc_khz = tgt_tsc_khz;
> +               kvm_xen_update_tsc_info(v);
>         }
>  
>         vcpu->hv_clock.tsc_timestamp = tsc_timestamp;
> diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
> index d7af40240248..46297521791c 100644
> --- a/arch/x86/kvm/xen.c
> +++ b/arch/x86/kvm/xen.c
> @@ -22,6 +22,9 @@
>  #include <xen/interface/event_channel.h>
>  #include <xen/interface/sched.h>
>  
> +#include <asm/xen/cpuid.h>
> +
> +#include "cpuid.h"
>  #include "trace.h"
>  
>  static int kvm_xen_set_evtchn(struct kvm_xen_evtchn *xe, struct kvm *kvm);
> @@ -2061,6 +2064,29 @@ void kvm_xen_destroy_vcpu(struct kvm_vcpu *vcpu)
>         del_timer_sync(&vcpu->arch.xen.poll_timer);
>  }
>  
> +void kvm_xen_update_tsc_info(struct kvm_vcpu *vcpu)
> +{
> +       struct kvm_cpuid_entry2 *entry;
> +       u32 function;
> +
> +       if (!vcpu->arch.xen.cpuid.base)
> +               return;
> +
> +       function = vcpu->arch.xen.cpuid.base | XEN_CPUID_LEAF(3);
> +       if (function > vcpu->arch.xen.cpuid.limit)
> +               return;
> +
> +       entry = kvm_find_cpuid_entry_index(vcpu, function, 1);
> +       if (entry) {
> +               entry->ecx = vcpu->arch.hv_clock.tsc_to_system_mul;
> +               entry->edx = vcpu->arch.hv_clock.tsc_shift;
> +       }
> +
> +       entry = kvm_find_cpuid_entry_index(vcpu, function, 2);
> +       if (entry)
> +               entry->eax = vcpu->arch.hw_tsc_khz;
> +}
> +
>  void kvm_xen_init_vm(struct kvm *kvm)
>  {
>         idr_init(&kvm->arch.xen.evtchn_ports);
> diff --git a/arch/x86/kvm/xen.h b/arch/x86/kvm/xen.h
> index ea33d80a0c51..88dd085e10f8 100644
> --- a/arch/x86/kvm/xen.h
> +++ b/arch/x86/kvm/xen.h
> @@ -32,6 +32,7 @@ int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *xe,
>  int kvm_xen_setup_evtchn(struct kvm *kvm,
>                          struct kvm_kernel_irq_routing_entry *e,
>                          const struct kvm_irq_routing_entry *ue);
> +void kvm_xen_update_tsc_info(struct kvm_vcpu *vcpu);
>  
>  static inline bool kvm_xen_msr_enabled(struct kvm *kvm)
>  {
> @@ -135,6 +136,10 @@ static inline bool kvm_xen_timer_enabled(struct kvm_vcpu *vcpu)
>  {
>         return false;
>  }
> +
> +static inline void kvm_xen_update_tsc_info(struct kvm_vcpu *vcpu)
> +{
> +}
>  #endif
>  
>  int kvm_xen_hypercall(struct kvm_vcpu *vcpu);
> @@ -143,6 +148,8 @@ int kvm_xen_hypercall(struct kvm_vcpu *vcpu);
>  #include <asm/xen/interface.h>
>  #include <xen/interface/vcpu.h>
>  
> +#define XEN_SIGNATURE "XenVMMXenVMM"
> +
>  void kvm_xen_update_runstate(struct kvm_vcpu *vcpu, int state);
>  
>  static inline void kvm_xen_runstate_set_running(struct kvm_vcpu *vcpu)

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