• KarimAllah Ahmed's avatar
    xen: Remove event channel notification through Xen PCI platform device · 72a9b186
    KarimAllah Ahmed authored
    Ever since commit 254d1a3f ("xen/pv-on-hvm kexec: shutdown watches
    from old kernel") using the INTx interrupt from Xen PCI platform
    device for event channel notification would just lockup the guest
    during bootup.  postcore_initcall now calls xs_reset_watches which
    will eventually try to read a value from XenStore and will get stuck
    on read_reply at XenBus forever since the platform driver is not
    probed yet and its INTx interrupt handler is not registered yet. That
    means that the guest can not be notified at this moment of any pending
    event channels and none of the per-event handlers will ever be invoked
    (including the XenStore one) and the reply will never be picked up by
    the kernel.
    
    The exact stack where things get stuck during xenbus_init:
    
    -xenbus_init
     -xs_init
      -xs_reset_watches
       -xenbus_scanf
        -xenbus_read
         -xs_single
          -xs_single
           -xs_talkv
    
    Vector callbacks have always been the favourite event notification
    mechanism since their introduction in commit 38e20b07 ("x86/xen:
    event channels delivery on HVM.") and the vector callback feature has
    always been advertised for quite some time by Xen that's why INTx was
    broken for several years now without impacting anyone.
    
    Luckily this also means that event channel notification through INTx
    is basically dead-code which can be safely removed without impacting
    anybody since it has been effectively disabled for more than 4 years
    with nobody complaining about it (at least as far as I'm aware of).
    
    This commit removes event channel notification through Xen PCI
    platform device.
    
    Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
    Cc: David Vrabel <david.vrabel@citrix.com>
    Cc: Juergen Gross <jgross@suse.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Cc: x86@kernel.org
    Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
    Cc: Bjorn Helgaas <bhelgaas@google.com>
    Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
    Cc: Julien Grall <julien.grall@citrix.com>
    Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
    Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
    Cc: Ross Lagerwall <ross.lagerwall@citrix.com>
    Cc: xen-devel@lists.xenproject.org
    Cc: linux-kernel@vger.kernel.org
    Cc: linux-pci@vger.kernel.org
    Cc: Anthony Liguori <aliguori@amazon.com>
    Signed-off-by: default avatarKarimAllah Ahmed <karahmed@amazon.de>
    Reviewed-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
    Signed-off-by: default avatarDavid Vrabel <david.vrabel@citrix.com>
    72a9b186
time.c 11.2 KB