Re: [BUG?] vhost assert error with < 4GB of RAM

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Jul 20, 2010 at 02:42:19PM -0600, Cam Macdonell wrote:
> I think I've found a bug when running a guest with vhost with less
> than 4GB of RAM.
> 
> If a guest has less than 4GB of RAM, then above_4g_mem_size is 0 for
> this call to cpu_register_physical_memory() in pc_memory_init() from
> hw/pc.c:922
> 
> #if TARGET_PHYS_ADDR_BITS > 32
>     cpu_register_physical_memory(0x100000000ULL, above_4g_mem_size,
>                                  ram_addr + below_4g_mem_size);
> #endif

Yes, the fix is in qemu already, it's a matter of merging into qemu-kvm.

> this leads to vhost_client_set_memory being called with size == 0
> 
> #3  0x00000000004301f3 in vhost_client_set_memory (client=0x113b010,
> start_addr=4294967296, size=0, phys_offset=3221225472)
>     at /home/cam/research/KVM/qemu-kvm/hw/vhost.c:312
> 
> which trips the assert at hw/vhost.c:312
> 
> static void vhost_client_set_memory(CPUPhysMemoryClient *client,
>                                     target_phys_addr_t start_addr,
>                                     ram_addr_t size,
>                                     ram_addr_t phys_offset)
> {
> 
> ...<snip>...
> 
>     assert(size);
> ...
> 
> something like the following fixes the problem but I'm not sure if
> it's the proper way to handle it.
> 
> diff --git a/exec.c b/exec.c
> index 5e9a5b7..991abfc 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2592,7 +2592,9 @@ void
> cpu_register_physical_memory_offset(target_phys_addr_t start_addr,
>      ram_addr_t orig_size = size;
>      subpage_t *subpage;
> 
> -    cpu_notify_set_memory(start_addr, size, phys_offset);
> +    if (size > 0) {
> +        cpu_notify_set_memory(start_addr, size, phys_offset);
> +    }
> 
>      if (phys_offset == IO_MEM_UNASSIGNED) {
>          region_offset = start_addr;