Re: [PATCH v3 17/28] hw/xen: add support for Xen primary console in emulated mode

["Durrant, Paul" <xadimgnik@gmail.com>]

On 25/10/2023 15:50, David Woodhouse wrote:
> From: David Woodhouse <dwmw@amazon.co.uk>
> 
> The primary console is special because the toolstack maps a page into
> the guest for its ring, and also allocates the guest-side event channel.
> The guest's grant table is even primed to export that page using a known
> grant ref#. Add support for all that in emulated mode, so that we can
> have a primary console.
> 
> For reasons unclear, the backends running under real Xen don't just use
> a mapping of the well-known GNTTAB_RESERVED_CONSOLE grant ref (which
> would also be in the ring-ref node in XenStore). Instead, the toolstack
> sets the ring-ref node of the primary console to the GFN of the guest
> page. The backend is expected to handle that special case and map it
> with foreignmem operations instead.
> 
> We don't have an implementation of foreignmem ops for emulated Xen mode,
> so just make it map GNTTAB_RESERVED_CONSOLE instead. This would probably
> work for real Xen too, but we can't work out how to make real Xen create
> a primary console of type "ioemu" to make QEMU drive it, so we can't
> test that; might as well leave it as it is for now under Xen.
> 
> Now at last we can boot the Xen PV shim and run PV kernels in QEMU.
> 
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> ---
>   hw/char/xen_console.c             |  78 ++++++++----
>   hw/i386/kvm/meson.build           |   1 +
>   hw/i386/kvm/trace-events          |   2 +
>   hw/i386/kvm/xen-stubs.c           |   8 ++
>   hw/i386/kvm/xen_gnttab.c          |   7 +-
>   hw/i386/kvm/xen_primary_console.c | 193 ++++++++++++++++++++++++++++++
>   hw/i386/kvm/xen_primary_console.h |  23 ++++
>   hw/i386/kvm/xen_xenstore.c        |  10 ++
>   hw/xen/xen-bus.c                  |   5 +
>   include/hw/xen/xen-bus.h          |   1 +
>   target/i386/kvm/xen-emu.c         |  23 +++-
>   11 files changed, 328 insertions(+), 23 deletions(-)
>   create mode 100644 hw/i386/kvm/xen_primary_console.c
>   create mode 100644 hw/i386/kvm/xen_primary_console.h
> 

Reviewed-by: Paul Durrant <paul@xen.org>