x86/paravirt: Prevent rtc_cmos platform device init on PV guests

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: Sander Eikelenboom <linux@eikelenboom.it>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Boris 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.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
(cherry picked from commit d8c98a1d1488747625ad6044d423406e17e99b7a)
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 8957810ad7d1e348dd6315242c3411a863745be6..42f16f6e8e759603fa0fbb741859a06b64a5ca76 100644 (file)
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -19,6 +19,12 @@ static inline int paravirt_enabled(void)
        return pv_info.paravirt_enabled;
 }
 
+static inline int paravirt_has_feature(unsigned int feature)
+{
+       WARN_ON_ONCE(!pv_info.paravirt_enabled);
+       return (pv_info.features & feature);
+}
+
 static inline void load_sp0(struct tss_struct *tss,
                             struct thread_struct *thread)
 {

diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index f7b0b5c112f28cc89c524231e9022b4560158b48..19d3a1304a94d7a2e8e600575ea771dff9afd8d1 100644 (file)
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -70,9 +70,14 @@ struct pv_info {
 #endif
 
        int paravirt_enabled;
+       unsigned int features;    /* valid only if paravirt_enabled is set */
        const char *name;
 };
 
+#define paravirt_has(x) paravirt_has_feature(PV_SUPPORTED_##x)
+/* Supported features */
+#define PV_SUPPORTED_RTC        (1<<0)
+
 struct pv_init_ops {
        /*
         * Patch may replace one of the defined code sequences with

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 23ba6765b718c790dbf698edbb2758a2ca6f9102..0838595c3d7daa7715c940bd621fa0a55bcadc25 100644 (file)
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -600,6 +600,7 @@ static inline unsigned long current_top_of_stack(void)
 #else
 #define __cpuid                        native_cpuid
 #define paravirt_enabled()     0
+#define paravirt_has(x)        0
 
 static inline void load_sp0(struct tss_struct *tss,
                            struct thread_struct *thread)

diff --git a/arch/x86/kernel/rtc.c b/arch/x86/kernel/rtc.c
index cd9685235df91b69f5e39885e55850964c67e8fc..4af8d063fb362cd2bf92b97a48fa8c1d5d95fd3b 100644 (file)
--- a/arch/x86/kernel/rtc.c
+++ b/arch/x86/kernel/rtc.c
@@ -200,6 +200,9 @@ static __init int add_rtc_cmos(void)
        }
 #endif
 
+       if (paravirt_enabled() && !paravirt_has(RTC))
+               return -ENODEV;
+
        platform_device_register(&rtc_device);
        dev_info(&rtc_device.dev,
                 "registered platform RTC device (no PNP device found)\n");

diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c
index 8f9a133cc09934c2de2fa77a1eecb14ce5f94c06..e9da4bcfe316a75539d80d203c948607af7d8026 100644 (file)
--- a/arch/x86/lguest/boot.c
+++ b/arch/x86/lguest/boot.c
@@ -1419,6 +1419,7 @@ __init void lguest_init(void)
        pv_info.kernel_rpl = 1;
        /* Everyone except Xen runs with this set. */
        pv_info.shared_kernel_pmd = 1;
+       pv_info.features = 0;
 
        /*
         * We set up all the lguest overrides for sensitive operations.  These

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 88b6729632b922aeb55e3f29595fe4bdad77a2fc..754b67255aa2850352dba14b4d8f2c5a6181c8e7 100644 (file)
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1163,7 +1163,7 @@ static const struct pv_info xen_info __initconst = {
 #ifdef CONFIG_X86_64
        .extra_user_64bit_cs = FLAT_USER_CS64,
 #endif
-
+       .features = 0,
        .name = "Xen",
 };
 
@@ -1507,6 +1507,8 @@ asmlinkage __visible void __init xen_start_kernel(void)
 
        /* Install Xen paravirt ops */
        pv_info = xen_info;
+       if (xen_initial_domain())
+               pv_info.features |= PV_SUPPORTED_RTC;
        pv_init_ops = xen_init_ops;
        pv_apic_ops = xen_apic_ops;
        if (!xen_pvh_domain()) {