Re: [PATCH v3 4/5] xen/arm: introduce GNTTABOP_cache_flush

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 08/10/14 14:00, Stefano Stabellini wrote:
> Introduce a new hypercall to perform cache maintenance operation on
> behalf of the guest. The argument is a machine address and a size. The
> implementation checks that the memory range is owned by the guest or the
> guest has been granted access to it by another domain.
>
> Introduce grant_map_exists: an internal grant table function to check
> whether an mfn has been granted to a given domain on a target grant
> table.
>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
>
> ---
>
> Changes in v3:
> - reduce the time the grant_table lock is held;
> - fix warning message;
> - s/EFAULT/EPERM;
> - s/llx/PRIx64;
> - check offset and size independetly before checking their sum;
> - rcu_lock_current_domain cannot fail;
> - s/ENOSYS/EOPNOTSUPP;
> - use clean_and_invalidate_xen_dcache_va_range to do both operations at
> once;
> - fold grant_map_exists in this patch;
> - support "count" argument;
> - make correspondent changes to compat/grant_table.c;
> - introduce GNTTAB_CACHE_SOURCE_GREF to select the type of input in the
> union;
> - rename size field to length;
> - make length and offset uint16_t;
> - only take spin_lock if d != owner.
>
> Changes in v2:
> - do not check for mfn_to_page errors;
> - take a reference to the page;
> - replace printk with gdprintk;
> - split long line;
> - remove out label;
> - move rcu_lock_current_domain down before the loop.
> - move the hypercall to GNTTABOP;
> - take a spin_lock before calling grant_map_exists.
> ---
>  xen/common/compat/grant_table.c  |    8 +++
>  xen/common/grant_table.c         |  135 ++++++++++++++++++++++++++++++++++++++
>  xen/include/public/grant_table.h |   20 ++++++
>  xen/include/xlat.lst             |    1 +
>  4 files changed, 164 insertions(+)
>
> diff --git a/xen/common/compat/grant_table.c b/xen/common/compat/grant_table.c
> index 6c00b09..4a3a23d 100644
> --- a/xen/common/compat/grant_table.c
> +++ b/xen/common/compat/grant_table.c
> @@ -51,6 +51,10 @@ CHECK_gnttab_get_version;
>  CHECK_gnttab_swap_grant_ref;
>  #undef xen_gnttab_swap_grant_ref
>  
> +#define xen_gnttab_cache_flush gnttab_cache_flush
> +CHECK_gnttab_cache_flush;
> +#undef xen_gnttab_cache_flush
> +
>  int compat_grant_table_op(unsigned int cmd,
>                            XEN_GUEST_HANDLE_PARAM(void) cmp_uop,
>                            unsigned int count)
> @@ -106,6 +110,10 @@ int compat_grant_table_op(unsigned int cmd,
>      CASE(swap_grant_ref);
>  #endif
>  
> +#ifndef CHECK_gnttab_cache_flush
> +    CASE(cache_flush);
> +#endif
> +
>  #undef CASE
>      default:
>          return do_grant_table_op(cmd, cmp_uop, count);
> diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c
> index a56a1bb..c16c11c 100644
> --- a/xen/common/grant_table.c
> +++ b/xen/common/grant_table.c
> @@ -501,6 +501,36 @@ static int _set_status(unsigned gt_version,
>          return _set_status_v2(domid, readonly, mapflag, shah, act, status);
>  }
>  
> +static bool_t grant_map_exists(const struct domain *ld,
> +                        struct grant_table *rgt,
> +                        unsigned long mfn)
> +{
> +    const struct active_grant_entry *act;
> +    grant_ref_t ref;
> +    bool_t ret = 0;
> +
> +    spin_is_locked(&rgt->lock);

This is now dead code.  spin_is_locked() is just a predicate.

> +
> +    for ( ref = 0; ref != nr_grant_entries(rgt); ref++ )
> +    {
> +        act = &active_entry(rgt, ref);
> +
> +        if ( !act->pin )
> +            continue;
> +
> +        if ( act->domid != ld->domain_id )
> +            continue;
> +
> +        if ( act->frame != mfn )
> +            continue;
> +
> +        ret = 1;
> +        break;

how about return 1 here...

> +    }
> +
> +    return ret;

and return 0 here?

> +}
> +
>  static void mapcount(
>      struct grant_table *lgt, struct domain *rd, unsigned long mfn,
>      unsigned int *wrc, unsigned int *rdc)
> @@ -2498,6 +2528,97 @@ gnttab_swap_grant_ref(XEN_GUEST_HANDLE_PARAM(gnttab_swap_grant_ref_t) uop,
>      return 0;
>  }
>  
> +static int __gnttab_cache_flush(gnttab_cache_flush_t cflush)

This should be passed via pointer.

> +{
> +    struct domain *d, *owner;
> +    struct page_info *page;
> +    uint64_t mfn;
> +    void *v;
> +
> +    if ( cflush.offset > PAGE_SIZE ||
> +            cflush.length > PAGE_SIZE ||
> +            cflush.offset + cflush.length > PAGE_SIZE )

Brackets, as per Xen style, please.

> +        return -EINVAL;
> +
> +    if ( cflush.length == 0 || cflush.op == 0 )
> +        return 0;
> +
> +    /* currently unimplemented */
> +    if ( cflush.op & GNTTAB_CACHE_SOURCE_GREF )
> +        return -EOPNOTSUPP;
> +
> +    d = rcu_lock_current_domain();
> +    mfn = cflush.a.dev_bus_addr >> PAGE_SHIFT;
> +
> +    if ( !mfn_valid(mfn) )
> +    {
> +        rcu_unlock_domain(d);
> +        return -EINVAL;
> +    }
> +
> +    page = mfn_to_page(mfn);
> +    owner = page_get_owner_and_reference(page);
> +    if ( !owner )
> +    {
> +        rcu_unlock_domain(d);
> +        return -EPERM;
> +    }
> +
> +    if ( d != owner )
> +    {
> +        spin_lock(&owner->grant_table->lock);
> +
> +        if ( !grant_map_exists(d, owner->grant_table, mfn) )
> +        {
> +            spin_unlock(&owner->grant_table->lock);
> +            rcu_unlock_domain(d);
> +            put_page(page);
> +            gdprintk(XENLOG_G_ERR, "mfn %"PRIx64" hasn't been granted by d%d to d%d\n",
> +                    mfn, owner->domain_id, d->domain_id);
> +            return -EINVAL;
> +        }
> +    }
> +
> +    v = map_domain_page(mfn);
> +    v += cflush.offset;
> +
> +    if ( (cflush.op & GNTTAB_CACHE_INVAL) && (cflush.op & GNTTAB_CACHE_CLEAN) )
> +        clean_and_invalidate_xen_dcache_va_range(v, cflush.length);
> +    else if ( cflush.op & GNTTAB_CACHE_INVAL )
> +        invalidate_xen_dcache_va_range(v, cflush.length);
> +    else if ( cflush.op & GNTTAB_CACHE_CLEAN )
> +        clean_xen_dcache_va_range(v, cflush.length);
> +
> +    if ( d != owner )
> +        spin_unlock(&owner->grant_table->lock);
> +    unmap_domain_page(v);
> +    put_page(page);
> +
> +    return 0;
> +}
> +
> +static long
> +gnttab_cache_flush(XEN_GUEST_HANDLE_PARAM(gnttab_cache_flush_t) uop,
> +                      unsigned int count)
> +{
> +    int i, ret;
> +    gnttab_cache_flush_t op;
> +
> +    for ( i = 0; i < count; i++ )

i must be unsigned, or this can be an infinite loop, as count in an
unverified user parameter at this point.

~Andrew

> +    {
> +        if ( i && hypercall_preempt_check() )
> +            return i;
> +        if ( unlikely(__copy_from_guest(&op, uop, 1)) )
> +            return -EFAULT;
> +        ret = __gnttab_cache_flush(op);
> +        if ( ret < 0 )
> +            return -ret;
> +        guest_handle_add_offset(uop, 1);
> +    }
> +    return 0;
> +}
> +
> +
>  long
>  do_grant_table_op(
>      unsigned int cmd, XEN_GUEST_HANDLE_PARAM(void) uop, unsigned int count)
> @@ -2627,6 +2748,20 @@ do_grant_table_op(
>          }
>          break;
>      }
> +    case GNTTABOP_cache_flush:
> +    {
> +        XEN_GUEST_HANDLE_PARAM(gnttab_cache_flush_t) cflush =
> +            guest_handle_cast(uop, gnttab_cache_flush_t);
> +        if ( unlikely(!guest_handle_okay(cflush, count)) )
> +            goto out;
> +        rc = gnttab_cache_flush(cflush, count);
> +        if ( rc > 0 )
> +        {
> +            guest_handle_add_offset(cflush, rc);
> +            uop = guest_handle_cast(cflush, void);
> +        }
> +        break;
> +    }
>      default:
>          rc = -ENOSYS;
>          break;
> diff --git a/xen/include/public/grant_table.h b/xen/include/public/grant_table.h
> index b8a3d6c..20d4e77 100644
> --- a/xen/include/public/grant_table.h
> +++ b/xen/include/public/grant_table.h
> @@ -309,6 +309,7 @@ typedef uint16_t grant_status_t;
>  #define GNTTABOP_get_status_frames    9
>  #define GNTTABOP_get_version          10
>  #define GNTTABOP_swap_grant_ref	      11
> +#define GNTTABOP_cache_flush	      12
>  #endif /* __XEN_INTERFACE_VERSION__ */
>  /* ` } */
>  
> @@ -574,6 +575,25 @@ struct gnttab_swap_grant_ref {
>  typedef struct gnttab_swap_grant_ref gnttab_swap_grant_ref_t;
>  DEFINE_XEN_GUEST_HANDLE(gnttab_swap_grant_ref_t);
>  
> +/*
> + * Issue one or more cache maintenance operations on a portion of a
> + * page granted to the calling domain by a foreign domain.
> + */
> +struct gnttab_cache_flush {
> +    union {
> +        uint64_t dev_bus_addr;
> +        grant_ref_t ref;
> +    } a;
> +    uint16_t offset; /* offset from start of grant */
> +    uint16_t length; /* size within the grant */
> +#define GNTTAB_CACHE_CLEAN          (1<<0)
> +#define GNTTAB_CACHE_INVAL          (1<<1)
> +#define GNTTAB_CACHE_SOURCE_GREF    (1<<31)
> +    uint32_t op;
> +};
> +typedef struct gnttab_cache_flush gnttab_cache_flush_t;
> +DEFINE_XEN_GUEST_HANDLE(gnttab_cache_flush_t);
> +
>  #endif /* __XEN_INTERFACE_VERSION__ */
>  
>  /*
> diff --git a/xen/include/xlat.lst b/xen/include/xlat.lst
> index 9a35dd7..3822b00 100644
> --- a/xen/include/xlat.lst
> +++ b/xen/include/xlat.lst
> @@ -51,6 +51,7 @@
>  ?       grant_entry_header              grant_table.h
>  ?	grant_entry_v2			grant_table.h
>  ?	gnttab_swap_grant_ref		grant_table.h
> +?	gnttab_cache_flush		grant_table.h
>  ?	kexec_exec			kexec.h
>  !	kexec_image			kexec.h
>  !	kexec_range			kexec.h