Re: [PATCH v2 2/5] EAL: Add new EAL "--qtest-virtio" option

On 2016/02/15 16:52, Tan, Jianfeng wrote:

Hi Tetsuya,

On 2/10/2016 11:40 AM, Tetsuya Mukawa wrote:

quoted

To work with qtest virtio-net PMD, virtual address that maps hugepages
should be between (1 << 31) to (1 << 44). This patch adds one more
option

Is there any reference about this limitation? And is it also true for
32 bit machine?

Hi Jianfeng,

44bit limitation is come from virtio legacy device spec.
The queue address register of virtio device is 32bit width.
And we should set page number to this register.
As a result, EAL memory should be under 44 bits.

I only support virtio modern device with this patch series.
So we can relax this limitation a bit.
(Next limitation may be 47 bits. It seems it is come from QEMU
implementation.)
But I guess 44bit limitation is still not so hard, also we can leave a
possibility to support legacy device.

31bits limitation is come from current memory mapping of QTest QEMU guest.
Here is.

 * ------------------------------------------------------------
 * Memory mapping of qtest quest
 * ------------------------------------------------------------
 * 0x00000000_00000000 - 0x00000000_3fffffff : not used
 * 0x00000000_40000000 - 0x00000000_40000fff : virtio-net(BAR1)
 * 0x00000000_40001000 - 0x00000000_40ffffff : not used
 * 0x00000000_41000000 - 0x00000000_417fffff : virtio-net(BAR4)
 * 0x00000000_41800000 - 0x00000000_41ffffff : not used
 * 0x00000000_42000000 - 0x00000000_420000ff : ivshmem(BAR0)
 * 0x00000000_42000100 - 0x00000000_42ffffff : not used
 * 0x00000000_80000000 - 0xffffffff_ffffffff : ivshmem(BAR2)

Thanks,
Tetsuya

Thanks,
Jianfeng