Re: [Xen-devel] [PATCH v3 15/28] x86/cpu: Sysctl and common infrastructure for levelling context switching

[Joao Martins <joao.m.martins@xxxxxxxxxx>]

On 03/15/2016 03:35 PM, Andrew Cooper wrote:
> A toolstack needs to know how much control Xen has over the visible cpuid
> values in PV guests.  Provide an explicit mechanism to query what Xen is
> capable of.
> 
> This interface will currently report no capabilities.  This change is
> scaffolding for future patches, which will introduce detection and switching
> logic, after which the interface will report hardware capabilities correctly.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> 
> v3:
>  * Reintroduce XEN_SYSCTL_get_levelling_caps (requested by Joao for some
>    libvirt development he has planned).
Hey Andrew,

Perhaps we got mixed in between threads but just to clarify: the exposure of
XEN_SYSCTL_get_levelling_caps isn't related to libvirt but rather related to
libxc cpuid policy[0] for supporting CPU topology on PV guests in the purpose of
the series I proposed here[1]. The libvirt related one was about the exposure of
featuresets (Patch 21) and/or stabilization of hw_caps format (Patch 2). My
apologies, if there was something I said that lead you into error.

Joao

[0] http://lists.xenproject.org/archives/html/xen-devel/2016-03/msg00397.html
[1] http://lists.xenproject.org/archives/html/xen-devel/2016-02/msg03115.html

>  * Rename to XEN_SYSCTL_get_cpu_levelling_caps, and rename the constants to
>    match the Xen command line options.
> v2:
>  * s/cpumasks/cpuidmasks/
> ---
>  xen/arch/x86/cpu/common.c        |  6 ++++++
>  xen/arch/x86/sysctl.c            |  6 ++++++
>  xen/include/asm-x86/cpufeature.h |  1 +
>  xen/include/asm-x86/processor.h  | 31 +++++++++++++++++++++++++++++++
>  xen/include/public/sysctl.h      | 23 +++++++++++++++++++++++
>  5 files changed, 67 insertions(+)
> 
> diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
> index a325dc0..dd32a94 100644
> --- a/xen/arch/x86/cpu/common.c
> +++ b/xen/arch/x86/cpu/common.c
> @@ -36,6 +36,12 @@ integer_param("cpuid_mask_ext_ecx", 
> opt_cpuid_mask_ext_ecx);
>  unsigned int opt_cpuid_mask_ext_edx = ~0u;
>  integer_param("cpuid_mask_ext_edx", opt_cpuid_mask_ext_edx);
>  
> +unsigned int __initdata expected_levelling_cap;
> +unsigned int __read_mostly levelling_caps;
> +
> +DEFINE_PER_CPU(struct cpuidmasks, cpuidmasks);
> +struct cpuidmasks __read_mostly cpuidmask_defaults;
> +
>  const struct cpu_dev *__read_mostly cpu_devs[X86_VENDOR_NUM] = {};
>  
>  unsigned int paddr_bits __read_mostly = 36;
> diff --git a/xen/arch/x86/sysctl.c b/xen/arch/x86/sysctl.c
> index 58cbd70..f68cbec 100644
> --- a/xen/arch/x86/sysctl.c
> +++ b/xen/arch/x86/sysctl.c
> @@ -190,6 +190,12 @@ long arch_do_sysctl(
>          }
>          break;
>  
> +    case XEN_SYSCTL_get_cpu_levelling_caps:
> +        sysctl->u.cpu_levelling_caps.caps = levelling_caps;
> +        if ( __copy_field_to_guest(u_sysctl, sysctl, 
> u.cpu_levelling_caps.caps) )
> +            ret = -EFAULT;
> +        break;
> +
>      default:
>          ret = -ENOSYS;
>          break;
> diff --git a/xen/include/asm-x86/cpufeature.h 
> b/xen/include/asm-x86/cpufeature.h
> index ed29d6f..50414e3 100644
> --- a/xen/include/asm-x86/cpufeature.h
> +++ b/xen/include/asm-x86/cpufeature.h
> @@ -81,6 +81,7 @@
>  #define cpu_has_xsavec               boot_cpu_has(X86_FEATURE_XSAVEC)
>  #define cpu_has_xgetbv1              boot_cpu_has(X86_FEATURE_XGETBV1)
>  #define cpu_has_xsaves               boot_cpu_has(X86_FEATURE_XSAVES)
> +#define cpu_has_hypervisor   boot_cpu_has(X86_FEATURE_HYPERVISOR)
>  
>  enum _cache_type {
>      CACHE_TYPE_NULL = 0,
> diff --git a/xen/include/asm-x86/processor.h b/xen/include/asm-x86/processor.h
> index ba907ee..9aa93db 100644
> --- a/xen/include/asm-x86/processor.h
> +++ b/xen/include/asm-x86/processor.h
> @@ -618,6 +618,37 @@ void microcode_set_module(unsigned int);
>  int microcode_update(XEN_GUEST_HANDLE_PARAM(const_void), unsigned long len);
>  int microcode_resume_cpu(unsigned int cpu);
>  
> +#define LCAP_faulting XEN_SYSCTL_CPU_LEVELCAP_faulting
> +#define LCAP_1cd      (XEN_SYSCTL_CPU_LEVELCAP_ecx |        \
> +                       XEN_SYSCTL_CPU_LEVELCAP_edx)
> +#define LCAP_e1cd     (XEN_SYSCTL_CPU_LEVELCAP_extd_ecx |   \
> +                       XEN_SYSCTL_CPU_LEVELCAP_extd_edx)
> +#define LCAP_Da1      XEN_SYSCTL_CPU_LEVELCAP_xsave_eax
> +#define LCAP_6c       XEN_SYSCTL_CPU_LEVELCAP_themal_ecx
> +#define LCAP_7ab0     (XEN_SYSCTL_CPU_LEVELCAP_l7s0_eax |   \
> +                       XEN_SYSCTL_CPU_LEVELCAP_17s0_ebx)
> +
> +/*
> + * Expected levelling capabilities (given cpuid vendor/family information),
> + * and levelling capabilities actually available (given MSR probing).
> + */
> +extern unsigned int expected_levelling_cap, levelling_caps;
> +
> +struct cpuidmasks
> +{
> +    uint64_t _1cd;
> +    uint64_t e1cd;
> +    uint64_t Da1;
> +    uint64_t _6c;
> +    uint64_t _7ab0;
> +};
> +
> +/* Per CPU shadows of masking MSR values, for lazy context switching. */
> +DECLARE_PER_CPU(struct cpuidmasks, cpuidmasks);
> +
> +/* Default masking MSR values, calculated at boot. */
> +extern struct cpuidmasks cpuidmask_defaults;
> +
>  enum get_cpu_vendor {
>     gcv_host_early,
>     gcv_host_late,
> diff --git a/xen/include/public/sysctl.h b/xen/include/public/sysctl.h
> index 96680eb..0dacca2 100644
> --- a/xen/include/public/sysctl.h
> +++ b/xen/include/public/sysctl.h
> @@ -766,6 +766,27 @@ struct xen_sysctl_tmem_op {
>  typedef struct xen_sysctl_tmem_op xen_sysctl_tmem_op_t;
>  DEFINE_XEN_GUEST_HANDLE(xen_sysctl_tmem_op_t);
>  
> +/*
> + * XEN_SYSCTL_get_cpu_levelling_caps (x86 specific)
> + *
> + * Return hardware capabilities concerning masking or faulting of the cpuid
> + * instruction for PV guests.
> + */
> +struct xen_sysctl_cpu_levelling_caps {
> +#define XEN_SYSCTL_CPU_LEVELCAP_faulting   (1ul <<  0) /* CPUID faulting    
> */
> +#define XEN_SYSCTL_CPU_LEVELCAP_ecx        (1ul <<  1) /* 0x00000001.ecx    
> */
> +#define XEN_SYSCTL_CPU_LEVELCAP_edx        (1ul <<  2) /* 0x00000001.edx    
> */
> +#define XEN_SYSCTL_CPU_LEVELCAP_extd_ecx   (1ul <<  3) /* 0x80000001.ecx    
> */
> +#define XEN_SYSCTL_CPU_LEVELCAP_extd_edx   (1ul <<  4) /* 0x80000001.edx    
> */
> +#define XEN_SYSCTL_CPU_LEVELCAP_xsave_eax  (1ul <<  5) /* 0x0000000D:1.eax  
> */
> +#define XEN_SYSCTL_CPU_LEVELCAP_themal_ecx (1ul <<  6) /* 0x00000006.ecx    
> */
> +#define XEN_SYSCTL_CPU_LEVELCAP_l7s0_eax   (1ul <<  7) /* 0x00000007:0.eax  
> */
> +#define XEN_SYSCTL_CPU_LEVELCAP_17s0_ebx   (1ul <<  8) /* 0x00000007:0.ebx  
> */
> +    uint32_t caps;
> +};
> +typedef struct xen_sysctl_cpu_levelling_caps xen_sysctl_cpu_levelling_caps_t;
> +DEFINE_XEN_GUEST_HANDLE(xen_sysctl_cpu_levelling_caps_t);
> +
>  struct xen_sysctl {
>      uint32_t cmd;
>  #define XEN_SYSCTL_readconsole                    1
> @@ -791,6 +812,7 @@ struct xen_sysctl {
>  #define XEN_SYSCTL_pcitopoinfo                   22
>  #define XEN_SYSCTL_psr_cat_op                    23
>  #define XEN_SYSCTL_tmem_op                       24
> +#define XEN_SYSCTL_get_cpu_levelling_caps        25
>      uint32_t interface_version; /* XEN_SYSCTL_INTERFACE_VERSION */
>      union {
>          struct xen_sysctl_readconsole       readconsole;
> @@ -816,6 +838,7 @@ struct xen_sysctl {
>          struct xen_sysctl_psr_cmt_op        psr_cmt_op;
>          struct xen_sysctl_psr_cat_op        psr_cat_op;
>          struct xen_sysctl_tmem_op           tmem_op;
> +        struct xen_sysctl_cpu_levelling_caps cpu_levelling_caps;
>          uint8_t                             pad[128];
>      } u;
>  };
> 

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