• David Vrabel's avatar
    x86/paravirt: Prevent rtc_cmos platform device init on PV guests · d8c98a1d
    David Vrabel authored
    Adding the rtc platform device in non-privileged Xen PV guests causes
    an IRQ conflict because these guests do not have legacy PIC and may
    allocate irqs in the legacy range.
    
    In a single VCPU Xen PV guest we should have:
    
    /proc/interrupts:
               CPU0
      0:       4934  xen-percpu-virq      timer0
      1:          0  xen-percpu-ipi       spinlock0
      2:          0  xen-percpu-ipi       resched0
      3:          0  xen-percpu-ipi       callfunc0
      4:          0  xen-percpu-virq      debug0
      5:          0  xen-percpu-ipi       callfuncsingle0
      6:          0  xen-percpu-ipi       irqwork0
      7:        321   xen-dyn-event     xenbus
      8:         90   xen-dyn-event     hvc_console
      ...
    
    But hvc_console cannot get its interrupt because it is already in use
    by rtc0 and the console does not work.
    
      genirq: Flags mismatch irq 8. 00000000 (hvc_console) vs. 00000000 (rtc0)
    
    We can avoid this problem by realizing that unprivileged PV guests (both
    Xen and lguests) are not supposed to have rtc_cmos device and so
    adding it is not necessary.
    
    Privileged guests (i.e. Xen's dom0) do use it but they should not have
    irq conflicts since they allocate irqs above legacy range (above
    gsi_top, in fact).
    
    Instead of explicitly testing whether the guest is privileged we can
    extend pv_info structure to include information about guest's RTC
    support.
    Reported-and-tested-by: default avatarSander Eikelenboom <linux@eikelenboom.it>
    Signed-off-by: default avatarDavid Vrabel <david.vrabel@citrix.com>
    Signed-off-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
    Cc: vkuznets@redhat.com
    Cc: xen-devel@lists.xenproject.org
    Cc: konrad.wilk@oracle.com
    Cc: stable@vger.kernel.org # 4.2+
    Link: http://lkml.kernel.org/r/1449842873-2613-1-git-send-email-boris.ostrovsky@oracle.comSigned-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    d8c98a1d
processor.h 20.7 KB