Re: [Xen-devel] [PATCH] Add a GNTTABOP to swap the content of two grant references under lock provided that they are not currently active.

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Wei Liu [mailto:wei.liu2@xxxxxxxxxx]
> Sent: 23 January 2012 03:51
> To: xen-devel@xxxxxxxxxxxxxxxxxxx
> Cc: Paul Durrant; Wei Liu (Intern)
> Subject: [PATCH] Add a GNTTABOP to swap the content of two grant
> references under lock provided that they are not currently active.
> 
> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>

Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>

> ---
>  xen/arch/x86/hvm/hvm.c           |    1 +
>  xen/common/grant_table.c         |   86
> ++++++++++++++++++++++++++++++++++++++
>  xen/include/public/grant_table.h |   18 +++++++-
>  xen/include/xlat.lst             |    1 +
>  4 files changed, 104 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c index
> b3d9ac0..c46bd3e 100644
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -2857,6 +2857,7 @@ static int grant_table_op_is_allowed(unsigned int
> cmd)
>      case GNTTABOP_copy:
>      case GNTTABOP_map_grant_ref:
>      case GNTTABOP_unmap_grant_ref:
> +    case GNTTABOP_swap_grant_ref:
>          return 1;
>      default:
>          /* all other commands need auditing */ diff --git
> a/xen/common/grant_table.c b/xen/common/grant_table.c index
> 34a49db..1147a3b 100644
> --- a/xen/common/grant_table.c
> +++ b/xen/common/grant_table.c
> @@ -2282,6 +2282,78 @@
> gnttab_get_version(XEN_GUEST_HANDLE(gnttab_get_version_t uop))
>      return 0;
>  }
> 
> +static s16
> +__gnttab_swap_grant_ref(unsigned long ref_a, unsigned long ref_b) {
> +    struct domain *d;
> +    struct active_grant_entry *act;
> +    s16 rc = GNTST_okay;
> +
> +    d = rcu_lock_current_domain();
> +
> +    spin_lock(&d->grant_table->lock);
> +
> +    act = &active_entry(d->grant_table, ref_a);
> +    if ( act->pin )
> +        PIN_FAIL(out, GNTST_eagain, "ref %ld busy\n", ref_a);
> +
> +    act = &active_entry(d->grant_table, ref_b);
> +    if ( act->pin )
> +        PIN_FAIL(out, GNTST_eagain, "ref %ld busy\n", ref_b);
> +
> +    if ( d->grant_table->gt_version == 1 ) {
> +        grant_entry_v1_t shared;
> +
> +        shared = shared_entry_v1(d->grant_table, ref_a);
> +
> +        shared_entry_v1(d->grant_table, ref_a) =
> +            shared_entry_v1(d->grant_table, ref_b);
> +
> +        shared_entry_v1(d->grant_table, ref_b) = shared;
> +    } else {
> +        grant_entry_v2_t shared;
> +        grant_status_t status;
> +
> +        shared = shared_entry_v2(d->grant_table, ref_a);
> +        status = status_entry(d->grant_table, ref_a);
> +
> +        shared_entry_v2(d->grant_table, ref_a) =
> +            shared_entry_v2(d->grant_table, ref_b);
> +        status_entry(d->grant_table, ref_a) =
> +            status_entry(d->grant_table, ref_b);
> +
> +        shared_entry_v2(d->grant_table, ref_b) = shared;
> +        status_entry(d->grant_table, ref_b) = status;
> +    }
> +
> +out:
> +    spin_unlock(&d->grant_table->lock);
> +
> +    rcu_unlock_domain(d);
> +
> +    return rc;
> +}
> +
> +static long
> +gnttab_swap_grant_ref(XEN_GUEST_HANDLE(gnttab_swap_grant_ref_t
> uop),
> +                      unsigned int count) {
> +    int i;
> +    gnttab_swap_grant_ref_t op;
> +
> +    for ( i = 0; i < count; i++ )
> +    {
> +        if ( i && hypercall_preempt_check() )
> +            return i;
> +        if ( unlikely(__copy_from_guest_offset(&op, uop, i, 1)) )
> +            return -EFAULT;
> +        op.status = __gnttab_swap_grant_ref(op.ref_a, op.ref_b);
> +        if ( unlikely(__copy_to_guest_offset(uop, i, &op, 1)) )
> +            return -EFAULT;
> +    }
> +    return 0;
> +}
> +
>  long
>  do_grant_table_op(
>      unsigned int cmd, XEN_GUEST_HANDLE(void) uop, unsigned int count)
> @@ -2400,6 +2472,20 @@ do_grant_table_op(
>          rc = gnttab_get_version(guest_handle_cast(uop,
> gnttab_get_version_t));
>          break;
>      }
> +    case GNTTABOP_swap_grant_ref:
> +    {
> +        XEN_GUEST_HANDLE(gnttab_swap_grant_ref_t) swap =
> +            guest_handle_cast(uop, gnttab_swap_grant_ref_t);
> +        if ( unlikely(!guest_handle_okay(swap, count)) )
> +            goto out;
> +        rc = gnttab_swap_grant_ref(swap, count);
> +        if ( rc > 0 )
> +        {
> +            guest_handle_add_offset(swap, rc);
> +            uop = guest_handle_cast(swap, void);
> +        }
> +        break;
> +    }
>      default:
>          rc = -ENOSYS;
>          break;
> diff --git a/xen/include/public/grant_table.h
> b/xen/include/public/grant_table.h
> index 0bf20bc..54d9551 100644
> --- a/xen/include/public/grant_table.h
> +++ b/xen/include/public/grant_table.h
> @@ -511,6 +511,20 @@ struct gnttab_get_version {  typedef struct
> gnttab_get_version gnttab_get_version_t;
> DEFINE_XEN_GUEST_HANDLE(gnttab_get_version_t);
> 
> +/*
> + * GNTTABOP_swap_grant_ref: Swap the contents of two grant entries.
> + */
> +#define GNTTABOP_swap_grant_ref            11
> +struct gnttab_swap_grant_ref {
> +    /* IN parameters */
> +    grant_ref_t ref_a;
> +    grant_ref_t ref_b;
> +    /* OUT parameters */
> +    int16_t status;             /* GNTST_* */
> +};
> +typedef struct gnttab_swap_grant_ref gnttab_swap_grant_ref_t;
> +DEFINE_XEN_GUEST_HANDLE(gnttab_swap_grant_ref_t);
> +
>  #endif /* __XEN_INTERFACE_VERSION__ */
> 
>  /*
> @@ -566,7 +580,7 @@ DEFINE_XEN_GUEST_HANDLE(gnttab_get_version_t);
>  #define GNTST_bad_page         (-9) /* Specified page was invalid for op.    
> */
>  #define GNTST_bad_copy_arg    (-10) /* copy arguments cross page
> boundary.   */
>  #define GNTST_address_too_big (-11) /* transfer page address too large.
> */
> -#define GNTST_eagain          (-12) /* Could not map at the moment. Retry.
> */
> +#define GNTST_eagain          (-12) /* Operation not done; try again.        
> */
> 
>  #define GNTTABOP_error_msgs {                   \
>      "okay",                                     \
> @@ -581,7 +595,7 @@ DEFINE_XEN_GUEST_HANDLE(gnttab_get_version_t);
>      "bad page",                                 \
>      "copy arguments cross page boundary",       \
>      "page address size too large",              \
> -    "could not map at the moment, retry"        \
> +    "operation not done; try again"             \
>  }
> 
>  #endif /* __XEN_PUBLIC_GRANT_TABLE_H__ */ diff --git
> a/xen/include/xlat.lst b/xen/include/xlat.lst index 3d92175..f602155 100644
> --- a/xen/include/xlat.lst
> +++ b/xen/include/xlat.lst
> @@ -50,6 +50,7 @@
>  ?    grant_entry_v1                  grant_table.h
>  ?       grant_entry_header              grant_table.h
>  ?    grant_entry_v2                  grant_table.h
> +?    gnttab_swap_grant_ref           grant_table.h
>  ?    kexec_exec                      kexec.h
>  !    kexec_image                     kexec.h
>  !    kexec_range                     kexec.h
> --
> 1.7.2.5


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