Re: [PATCH v2 2/4] vhost-user: introduce virtio API

[Laurent Vivier <lvivier@redhat.com>]

On 17/07/2024 07:21, David Gibson wrote:
> On Fri, Jul 12, 2024 at 05:32:42PM +0200, Laurent Vivier wrote:
>> Add virtio.c and virtio.h that define the functions needed
>> to manage virtqueues.
>>
>> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
>> ---
>>   Makefile |   4 +-
>>   util.h   |  11 +
>>   virtio.c | 611 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>   virtio.h | 190 +++++++++++++++++
>>   4 files changed, 814 insertions(+), 2 deletions(-)
>>   create mode 100644 virtio.c
>>   create mode 100644 virtio.h
>>
...
>> +
>> +/**
>> + * struct vu_dev_region - guest shared memory region
>> + * @gpa:		Guest physical address of the region
>> + * @size:		Memory size in bytes
>> + * @qva:		QEMU virtual address
> 
> Is this actually the qemu virtual address? Or is it our virtual
> address?
> 

It is actually QEMU virtual address, it's a virtual address provided by the front-end (in 
our case QEMU).

https://qemu-project.gitlab.io/qemu/interop/vhost-user.html#memory-region-description

It's used in qva_to_va() to convert vring addresses that are in QEMU userspace 
(vhost-user) to our process userspace mapped address, while vu_gpa_to_va() is used to 
convert guest physical address (virtio) of buffers address stored vring descritors that 
are in guest physical address space to our process address space.

vhost-user addresses are in QEMU virtual adress space, virtio addresses are in guest 
physical address space.


Thansk,
Laurent