Re: [PATCH] accel/xen: Fix DM state change notification in dm_restrict mode

[Paul Durrant <xadimgnik@xxxxxxxxx>]

On 14/03/2023 08:35, David Woodhouse wrote:
> From: David Woodhouse <dwmw@xxxxxxxxxxxx>
>
> When dm_restrict is set, QEMU isn't permitted to update the XenStore node
> to indicate its running status. Previously, the xs_write() call would fail
> but the failure was ignored.
>
> However, in refactoring to allow for emulated XenStore operations, a new
> call to xs_open() was added. That one didn't fail gracefully, causing a
> fatal error when running in dm_restrict mode.
>
> Partially revert the offending patch, removing the additional call to
> xs_open() because the global 'xenstore' variable is still available; it
> just needs to be used with qemu_xen_xs_write() now instead of directly
> with the xs_write() libxenstore function.
>
> Also make the whole thing conditional on !xen_domid_restrict. There's no
> point even registering the state change handler to attempt to update the
> XenStore node when we know it's destined to fail.
>
> Fixes: ba2a92db1ff6 ("hw/xen: Add xenstore operations to allow redirection to 
> internal emulation")
> Reported-by: Jason Andryuk <jandryuk@xxxxxxxxx>
> Co-developed-by: Jason Andryuk <jandryuk@xxxxxxxxx>
> Not-Signed-off-by: Jason Andryuk <jandryuk@xxxxxxxxx>
> Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
> Will-be-Tested-by: Jason Andryuk <jandryuk@xxxxxxxxx>
> ---
>   accel/xen/xen-all.c | 27 ++++++++++-----------------
>   1 file changed, 10 insertions(+), 17 deletions(-)
Reviewed-by: Paul Durrant <paul@xxxxxxx>