linux-kernel - [PATCH] x86: Xen PV guests don't have the rtc

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Date:	Wed,  9 Dec 2015 09:32:49 -0500
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org, vkuznets@...hat.com,
	linux@...elenboom.it, xen-devel@...ts.xenproject.org,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	David Vrabel <david.vrabel@...rix.com>, stable@...r.kernel.org
Subject: [PATCH] x86: Xen PV guests don't have the rtc_cmos platform device

Adding the rtc platform device in a Xen PV guests causes an IRQ
conflict because these guests do not have a legacy PIC.

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)

So don't add the rtc_cmos device in Xen PV guests. (In fact, don't add
it to any paravirt_enabled() guest since lguest is also unable to probe
this device)

Reported-by: Sander Eikelenboom <linux@...elenboom.it>
Signed-off-by: David Vrabel <david.vrabel@...rix.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Tested-by: Sander Eikelenboom <linux@...elenboom.it>
Cc: stable@...r.kernel.org
---
 arch/x86/kernel/rtc.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/rtc.c b/arch/x86/kernel/rtc.c
index cd96852..dd4d6d9 100644
--- 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())
+		return -ENODEV;
+
 	platform_device_register(&rtc_device);
 	dev_info(&rtc_device.dev,
 		 "registered platform RTC device (no PNP device found)\n");
-- 
1.8.1.4

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