Re: [v4][PATCH 2/9] xen:x86: define a new hypercall to get RMRR mappings

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

On 22/08/14 11:09, Tiejun Chen wrote:
> We need this new hypercall to get RMRR mapping for VM.
>
> Signed-off-by: Tiejun Chen <tiejun.chen@intel.com>
> ---
>  xen/arch/x86/mm.c           | 71 +++++++++++++++++++++++++++++++++++++++++++++
>  xen/include/public/memory.h | 37 ++++++++++++++++++++++-
>  2 files changed, 107 insertions(+), 1 deletion(-)
>
> diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
> index d23cb3f..e0d6650 100644
> --- a/xen/arch/x86/mm.c
> +++ b/xen/arch/x86/mm.c
> @@ -123,6 +123,7 @@
>  #include <asm/setup.h>
>  #include <asm/fixmap.h>
>  #include <asm/pci.h>
> +#include <asm/acpi.h>
>  
>  /* Mapping of the fixmap space needed early. */
>  l1_pgentry_t __attribute__ ((__section__ (".bss.page_aligned")))
> @@ -4842,6 +4843,76 @@ long arch_memory_op(unsigned long cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
>          return rc;
>      }
>  
> +    case XENMEM_reserved_device_memory_map:
> +    {
> +        struct xen_reserved_device_memory_map map;
> +        XEN_GUEST_HANDLE(xen_reserved_device_memory_t) buffer;
> +        XEN_GUEST_HANDLE_PARAM(xen_reserved_device_memory_t) buffer_param;
> +        unsigned int i = 0;
> +        static unsigned int nr_entries = 0;
> +        static struct xen_reserved_device_memory *rmrr_map;

Absolutely not.  This hypercall can easy be run concurrently.

> +        struct acpi_rmrr_unit *rmrr;
> +
> +        if ( copy_from_guest(&map, arg, 1) )
> +            return -EFAULT;
> +
> +        if ( !nr_entries )
> +            /* Currently we just need to cover RMRR. */
> +            list_for_each_entry( rmrr, &acpi_rmrr_units, list )
> +                nr_entries++;

Maintain a global count as entries are added/removed from this list.  It
is a waste of time recounting this list for each hypercall.

> +
> +        if ( !nr_entries )
> +                return -ENOENT;
> +        else
> +        {
> +            if ( rmrr_map == NULL )
> +            {
> +                rmrr_map = xmalloc_array(xen_reserved_device_memory_t,
> +                                         nr_entries);

You can do all of this without any memory allocation.

> +                if ( rmrr_map == NULL )
> +                {
> +                    return -ENOMEM;
> +                }
> +
> +                list_for_each_entry( rmrr, &acpi_rmrr_units, list )
> +                {
> +                    rmrr_map[i].pfn = rmrr->base_address >> PAGE_SHIFT;
> +                    rmrr_map[i].count = PAGE_ALIGN(rmrr->end_address -
> +                                                   rmrr->base_address) /
> +                                                   PAGE_SIZE;
> +                    i++;
> +                }
> +            }
> +        }
> +
> +        if ( map.nr_entries < nr_entries )
> +        {
> +            map.nr_entries =  nr_entries;
> +            if ( copy_to_guest(arg, &map, 1) )
> +                return -EFAULT;
> +            return -ENOBUFS;
> +        }
> +
> +        map.nr_entries =  nr_entries;
> +        buffer_param = guest_handle_cast(map.buffer,
> +                                         xen_reserved_device_memory_t);
> +        buffer = guest_handle_from_param(buffer_param,
> +                                         xen_reserved_device_memory_t);
> +        if ( !guest_handle_okay(buffer, map.nr_entries) )
> +            return -EFAULT;
> +
> +        for ( i = 0; i < map.nr_entries; ++i )
> +        {
> +            if ( copy_to_guest_offset(buffer, i, rmrr_map + i, 1) )
> +                return -EFAULT;
> +        }
> +
> +        if ( copy_to_guest(arg, &map, 1) )
> +                return -EFAULT;
> +
> +        return 0;
> +    }
> +
>      default:
>          return subarch_memory_op(cmd, arg);
>      }
> diff --git a/xen/include/public/memory.h b/xen/include/public/memory.h
> index 2c57aa0..8481843 100644
> --- a/xen/include/public/memory.h
> +++ b/xen/include/public/memory.h
> @@ -523,7 +523,42 @@ DEFINE_XEN_GUEST_HANDLE(xen_mem_sharing_op_t);
>  
>  #endif /* defined(__XEN__) || defined(__XEN_TOOLS__) */
>  
> -/* Next available subop number is 26 */
> +/*
> + * Some devices may reserve some range.

"range" is not a useful unit of measure.

> + *
> + * Currently we just have RMRR
> + * - Reserved memory Region Reporting Structure,
> + * So returns the RMRR memory map as it was when the domain
> + * was started.
> + */
> +#define XENMEM_reserved_device_memory_map   26
> +struct xen_reserved_device_memory {

xen_mem_ to match the prevailing style

> +    /* PFN of the current mapping of the page. */
> +    xen_pfn_t pfn;
> +    /* Number of the current mapping pages. */
> +    xen_ulong_t count;
> +};

This struct marks a range, but the fields don't make it clear.  I would
suggest "start" and "nr_frames" as names.

~Andrew

> +typedef struct xen_reserved_device_memory xen_reserved_device_memory_t;
> +DEFINE_XEN_GUEST_HANDLE(xen_reserved_device_memory_t);
> +
> +struct xen_reserved_device_memory_map {
> +    /*
> +     * On call the number of entries which can be stored in buffer. On
> +     * return the number of entries which have been stored in
> +     * buffer.
> +     */
> +    unsigned int nr_entries;
> +
> +    /*
> +     * Entries in the buffer are in the same format as
> +     * xen_reserved_device_memory.
> +     */
> +    XEN_GUEST_HANDLE(void) buffer;
> +};
> +typedef struct xen_reserved_device_memory_map xen_reserved_device_memory_map_t;
> +DEFINE_XEN_GUEST_HANDLE(xen_reserved_device_memory_map_t);
> +
> +/* Next available subop number is 27 */
>  
>  #endif /* __XEN_PUBLIC_MEMORY_H__ */
>