• Boris Ostrovsky's avatar
    xen: Revert commits da72ff5b and 72a9b186 · 3ed024e2
    Boris Ostrovsky authored
    commit 84d582d2 upstream.
    
    Recent discussion (http://marc.info/?l=xen-devel&m=149192184523741)
    established that commit 72a9b186 ("xen: Remove event channel
    notification through Xen PCI platform device") (and thus commit
    da72ff5b ("partially revert "xen: Remove event channel
    notification through Xen PCI platform device"")) are unnecessary and,
    in fact, prevent HVM guests from booting on Xen releases prior to 4.0
    
    Therefore we revert both of those commits.
    
    The summary of that discussion is below:
    
      Here is the brief summary of the current situation:
    
      Before the offending commit (72a9b186):
    
      1) INTx does not work because of the reset_watches path.
      2) The reset_watches path is only taken if you have Xen > 4.0
      3) The Linux Kernel by default will use vector inject if the hypervisor
         support. So even INTx does not work no body running the kernel with
         Xen > 4.0 would notice. Unless he explicitly disabled this feature
         either in the kernel or in Xen (and this can only be disabled by
         modifying the code, not user-supported way to do it).
    
      After the offending commit (+ partial revert):
    
      1) INTx is no longer support for HVM (only for PV guests).
      2) Any HVM guest The kernel will not boot on Xen < 4.0 which does
         not have vector injection support. Since the only other mode
         supported is INTx which.
    
      So based on this summary, I think before commit (72a9b186) we were
      in much better position from a user point of view.
    Signed-off-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
    Reviewed-by: default avatarJuergen Gross <jgross@suse.com>
    Cc: Boris Ostrovsky <boris.ostrovsky@oracle.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 <sstabellini@kernel.org>
    Cc: Julien Grall <julien.grall@arm.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>
    Cc: KarimAllah Ahmed <karahmed@amazon.de>
    Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    3ed024e2
smp.c 18.1 KB