Re: [Xen-devel] [PATCH v15 02/11] x86: add generic resource (e.g. MSR) access hypercall

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 05/09/14 09:37, Chao Peng wrote:
> Add a generic resource access hypercall for tool stack or other
> components, e.g., accessing MSR, port I/O, etc.
>
> Signed-off-by: Dongxiao Xu <dongxiao.xu@xxxxxxxxx>
> Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
> ---
>  xen/arch/x86/platform_hypercall.c |   63 
> +++++++++++++++++++++++++++++++++++++
>  xen/include/public/platform.h     |   15 +++++++++
>  xen/include/xlat.lst              |    1 +
>  3 files changed, 79 insertions(+)
>
> diff --git a/xen/arch/x86/platform_hypercall.c 
> b/xen/arch/x86/platform_hypercall.c
> index 2162811..e5ad4c9 100644
> --- a/xen/arch/x86/platform_hypercall.c
> +++ b/xen/arch/x86/platform_hypercall.c
> @@ -61,6 +61,42 @@ long cpu_down_helper(void *data);
>  long core_parking_helper(void *data);
>  uint32_t get_cur_idle_nums(void);
>  
> +struct xen_resource_access {
> +    int32_t ret;
> +    struct xenpf_resource_op *data;
> +};
> +
> +static bool_t allow_access_msr(unsigned int msr)
> +{
> +    return 0;
> +}
> +
> +static void resource_access_one(void *info)
> +{
> +    struct xen_resource_access *ra = info;
> +    int ret = 0;
> +
> +    switch ( ra->data->cmd )
> +    {
> +    case XEN_RESOURCE_OP_MSR_READ:
> +    case XEN_RESOURCE_OP_MSR_WRITE:
> +        if ( ra->data->idx >> 32 )
> +            ret = -EINVAL;
> +        else if ( !allow_access_msr(ra->data->idx) )
> +            ret = -EACCES;
> +        else if ( ra->data->cmd == XEN_RESOURCE_OP_MSR_READ )
> +            ret = rdmsr_safe(ra->data->idx, ra->data->val);
> +        else
> +            ret = wrmsr_safe(ra->data->idx, ra->data->val);
> +        break;
> +    default:
> +        ret = -EINVAL;
> +        break;
> +    }
> +
> +    ra->ret = ret;
> +}
> +
>  ret_t do_platform_op(XEN_GUEST_HANDLE_PARAM(xen_platform_op_t) u_xenpf_op)
>  {
>      ret_t ret = 0;
> @@ -601,6 +637,33 @@ ret_t 
> do_platform_op(XEN_GUEST_HANDLE_PARAM(xen_platform_op_t) u_xenpf_op)
>      }
>      break;
>  
> +    case XENPF_resource_op:
> +    {
> +        struct xen_resource_access ra;
> +        struct xenpf_resource_op *rsc_op = &op->u.resource_op;
> +        unsigned int cpu = smp_processor_id();
> +
> +        ra.data = rsc_op;
> +
> +        if ( rsc_op->cpu == cpu )
> +            resource_access_one(&ra);
> +        else if ( cpu_online(rsc_op->cpu) )
> +            on_selected_cpus(cpumask_of(rsc_op->cpu),

You must validate rsc_op->cpu before using it.  cpumask_of(something
large) will happily wander off the end of an array.

> +                         resource_access_one, &ra, 1);
> +        else
> +        {
> +            ret = -ENODEV;
> +            break;
> +        }
> +
> +        if ( ra.ret )
> +        {
> +            ret = ra.ret;
> +            break;
> +        }
> +    }
> +    break;
> +
>      default:
>          ret = -ENOSYS;
>          break;
> diff --git a/xen/include/public/platform.h b/xen/include/public/platform.h
> index 053b9fa..3ed50de 100644
> --- a/xen/include/public/platform.h
> +++ b/xen/include/public/platform.h
> @@ -527,6 +527,20 @@ struct xenpf_core_parking {
>  typedef struct xenpf_core_parking xenpf_core_parking_t;
>  DEFINE_XEN_GUEST_HANDLE(xenpf_core_parking_t);
>  
> +#define XENPF_resource_op   61
> +
> +#define XEN_RESOURCE_OP_MSR_READ  0
> +#define XEN_RESOURCE_OP_MSR_WRITE 1
> +
> +struct xenpf_resource_op {
> +    uint16_t cmd;       /* XEN_RESOURCE_OP_* */

There is an alignment issue here between 32 and 64bit. Putting an an
explicit unit16_t _resd; field should fix it.

~Andrew

> +    uint32_t cpu;
> +    uint64_t idx;
> +    uint64_t val;
> +};
> +typedef struct xenpf_resource_op xenpf_resource_op_t;
> +DEFINE_XEN_GUEST_HANDLE(xenpf_resource_op_t);
> +
>  /*
>   * ` enum neg_errnoval
>   * ` HYPERVISOR_platform_op(const struct xen_platform_op*);
> @@ -553,6 +567,7 @@ struct xen_platform_op {
>          struct xenpf_cpu_hotadd        cpu_add;
>          struct xenpf_mem_hotadd        mem_add;
>          struct xenpf_core_parking      core_parking;
> +        struct xenpf_resource_op       resource_op;
>          uint8_t                        pad[128];
>      } u;
>  };
> diff --git a/xen/include/xlat.lst b/xen/include/xlat.lst
> index 9a35dd7..06ed7b9 100644
> --- a/xen/include/xlat.lst
> +++ b/xen/include/xlat.lst
> @@ -88,6 +88,7 @@
>  ?    xenpf_enter_acpi_sleep          platform.h
>  ?    xenpf_pcpuinfo                  platform.h
>  ?    xenpf_pcpu_version              platform.h
> +?    xenpf_resource_op               platform.h
>  !    sched_poll                      sched.h
>  ?    sched_remote_shutdown           sched.h
>  ?    sched_shutdown                  sched.h


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