From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tetsuya Mukawa <mukawa@igel.co.jp>
Subject: Re: [PATCH v2 2/5] EAL: Add new EAL "--qtest-virtio"
	option
Date: Tue, 16 Feb 2016 10:32:39 +0900
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To: "Tan, Jianfeng" <jianfeng.tan@intel.com>, dev@dpdk.org
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On 2016/02/15 16:52, Tan, Jianfeng wrote:
> Hi Tetsuya,
>
> On 2/10/2016 11:40 AM, Tetsuya Mukawa wrote:
>> 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