From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Chen, Tiejun" <tiejun.chen@intel.com>
Subject: Re: [PATCH v12] introduce
	XENMEM_reserved_device_memory_map
Date: Wed, 22 Jul 2015 20:55:11 +0800
Message-ID: <55AF92AF.4080107@intel.com>
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Cc: Kevin Tian <kevin.tian@intel.com>, Keir Fraser <keir@xen.org>, Tim Deegan <tim@xen.org>, Ian Jackson <Ian.Jackson@eu.citrix.com>, Ian Campbell <Ian.Campbell@eu.citrix.com>, Yang Z Zhang <yang.z.zhang@intel.com>
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> +#ifdef HAS_PASSTHROUGH
> +        case XENMEM_reserved_device_memory_map:
> +        {
> +            struct get_reserved_device_memory grdm;
> +
> +            if ( unlikely(start_extent) )
> +                return -ENOSYS;
> +
> +            if ( copy_from_guest(&grdm.map, compat, 1) ||
> +                 !compat_handle_okay(grdm.map.buffer, grdm.map.nr_entries) )
> +                return -EFAULT;
> +
> +            if ( grdm.map.flags & ~XENMEM_RDM_ALL )
> +                return -EINVAL;
> +
> +            grdm.used_entries = 0;
> +            rc = iommu_get_reserved_device_memory(get_reserved_device_memory,
> +                                                  &grdm);
> +

Just as you asked me previously,

Here if RDM doesn't exist, so

grdm.map.nr_entries = grdm.used_entries = 0, and rc = 0, right?

> +            if ( !rc && grdm.map.nr_entries < grdm.used_entries )
> +                rc = -ENOBUFS;
> +            grdm.map.nr_entries = grdm.used_entries;
> +            if ( __copy_to_guest(compat, &grdm.map, 1) )

So can we still do this copy here?

Thanks
Tiejun