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Date: Fri, 11 Jul 2014 22:56:41 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 2/3] vhost-user: Fix VHOST_SET_MEM_TABLE
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To: snabb-devel@googlegroups.com, qemu-devel@nongnu.org, mst@redhat.com
Cc: tech@virtualopensystems.com, n.nikolaev@virtualopensystems.com

Il 08/07/2014 16:06, Nikolay Nikolaev ha scritto:
> @@ -216,6 +216,10 @@ static int vhost_user_call(struct vhost_dev *dev, unsigned long int request,
>      case VHOST_SET_MEM_TABLE:
>          for (i = 0; i < dev->mem->nregions; ++i) {
>              struct vhost_memory_region *reg = dev->mem->regions + i;
> +            if (!qemu_is_ram_block(reg->guest_phys_addr)) {
> +                /* this is non-RAM region - skip it */
> +                continue;
> +            }
>              fd = qemu_get_ram_fd(reg->guest_phys_addr);
>              if (fd > 0) {
>                  msg.memory.regions[fd_num].userspace_addr = reg->userspace_addr;

This is wrong.  qemu_get_ram_fd doesn't accept a guest physical address. 
  ram_addr_t are opaque values that are assigned in qemu_ram_alloc.

In fact, RAM regions are filtered by

static bool vhost_section(MemoryRegionSection *section)
{
     return memory_region_is_ram(section->mr);
}


You can find the ram_addr_t corresponding to the userspace_addr using 
qemu_ram_addr_from_host, and then call qemu_get_ram_fd on it.

Paolo