Re: [Xen-devel] GPU passthrough issue when VM is configured with 4G memory

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 13 Mar 2013, Hanweidong wrote:
> MMIO HOLE was adjusted to e0000000 - fc000000. But QEMU uses below code to 
> init 
> RAM in xen_ram_init: 
> 
>     ...
>     block_len = ram_size;
>     if (ram_size >= HVM_BELOW_4G_RAM_END) {
>         /* Xen does not allocate the memory continuously, and keep a hole at
>          * HVM_BELOW_4G_MMIO_START of HVM_BELOW_4G_MMIO_LENGTH
>          */
>         block_len += HVM_BELOW_4G_MMIO_LENGTH;
>     }
>     memory_region_init_ram(&ram_memory, "xen.ram", block_len);
>     vmstate_register_ram_global(&ram_memory);
> 
>     if (ram_size >= HVM_BELOW_4G_RAM_END) {
>         above_4g_mem_size = ram_size - HVM_BELOW_4G_RAM_END;
>         below_4g_mem_size = HVM_BELOW_4G_RAM_END;
>     } else {
>         below_4g_mem_size = ram_size;
>     }
>     ...
> 
> HVM_BELOW_4G_RAM_END is f0000000. If we change HVM_BELOW_4G_RAM_END to 
> e0000000, 
> Which it's consistent with hvmloader when assigning a GPU, and then guest 
> worked 
> for us. So we wondering that xen_ram_init in QEMU should be consistent with 
> hvmloader. 
> 
> In addition, we found QEMU uses hardcode 0xe0000000 in pc_init1() as below. 
> Should keep these places handle the consistent mmio hole or not?
> 
>     if (ram_size >= 0xe0000000 ) {
>         above_4g_mem_size = ram_size - 0xe0000000;
>         below_4g_mem_size = 0xe0000000;
>     } else {
>         above_4g_mem_size = 0;
>         below_4g_mem_size = ram_size;
>     }

The guys at Intel sent a couple of patches recently to fix this issue:

http://marc.info/?l=xen-devel&m=136150317011027
http://marc.info/?l=qemu-devel&m=136177475215360&w=2

Do they solve your problem?

Xudong and Xiantao,
are you going to send an update of the second patch to QEMU?

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