* A better fix for the Xen clock problem.

svn path=/nixpkgs/trunk/; revision=24488

pkgs/os-specific/linux/kernel/patches.nix

@@ -214,9 +214,10 @@ in
       patch = ./guruplug-mach-type.patch;
     };
 
-  revert_pvclock_sync =
+  xen_pvclock_resume =
-    { name = "revert-pvclock-sync";
+    { # Fix the clock after a DomU restore following a Dom0 reboot or migration.
-      patch = ./revert-pvclock-sync.patch;
+      name = "xen-pvclock-resume";
+      patch = ./xen-pvclock-resume.patch;
     };
   
 }

pkgs/os-specific/linux/kernel/revert-pvclock-sync.patch

@@ -1,46 +0,0 @@
-diff -ru -x '*~' linux-2.6.32.24-orig/arch/x86/kernel/pvclock.c linux-2.6.32.24/arch/x86/kernel/pvclock.c
---- linux-2.6.32.24-orig/arch/x86/kernel/pvclock.c	2010-10-01 22:51:56.000000000 +0200
-+++ linux-2.6.32.24/arch/x86/kernel/pvclock.c	2010-10-25 14:02:14.000000000 +0200
-@@ -109,14 +109,11 @@
- 	return pv_tsc_khz;
- }
- 
--static atomic64_t last_value = ATOMIC64_INIT(0);
--
- cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
- {
- 	struct pvclock_shadow_time shadow;
- 	unsigned version;
- 	cycle_t ret, offset;
--	u64 last;
- 
- 	do {
- 		version = pvclock_get_time_values(&shadow, src);
-@@ -126,27 +123,6 @@
- 		barrier();
- 	} while (version != src->version);
- 
--	/*
--	 * Assumption here is that last_value, a global accumulator, always goes
--	 * forward. If we are less than that, we should not be much smaller.
--	 * We assume there is an error marging we're inside, and then the correction
--	 * does not sacrifice accuracy.
--	 *
--	 * For reads: global may have changed between test and return,
--	 * but this means someone else updated poked the clock at a later time.
--	 * We just need to make sure we are not seeing a backwards event.
--	 *
--	 * For updates: last_value = ret is not enough, since two vcpus could be
--	 * updating at the same time, and one of them could be slightly behind,
--	 * making the assumption that last_value always go forward fail to hold.
--	 */
--	last = atomic64_read(&last_value);
--	do {
--		if (ret < last)
--			return last;
--		last = atomic64_cmpxchg(&last_value, last, ret);
--	} while (unlikely(last != ret));
--
- 	return ret;
- }
- 

pkgs/os-specific/linux/kernel/xen-pvclock-resume.patch

@@ -0,0 +1,51 @@
+From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
+Date: Mon, 25 Oct 2010 16:53:46 -0700
+Subject: [PATCH] x86/pvclock: zero last_value on resume
+
+If the guest domain has been suspend/resumed or migrated, then the
+system clock backing the pvclock clocksource may revert to a smaller
+value (ie, can be non-monotonic across the migration/save-restore).
+Make sure we zero last_value in that case so that the domain
+continues to see clock updates.
+
+Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
+
+diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
+index cd02f32..6226870 100644
+--- a/arch/x86/include/asm/pvclock.h
++++ b/arch/x86/include/asm/pvclock.h
+@@ -11,5 +11,6 @@ unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src);
+ void pvclock_read_wallclock(struct pvclock_wall_clock *wall,
+ 			    struct pvclock_vcpu_time_info *vcpu,
+ 			    struct timespec *ts);
++void pvclock_resume(void);
+ 
+ #endif /* _ASM_X86_PVCLOCK_H */
+diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
+index 239427c..a4f07c1 100644
+--- a/arch/x86/kernel/pvclock.c
++++ b/arch/x86/kernel/pvclock.c
+@@ -120,6 +120,11 @@ unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src)
+ 
+ static atomic64_t last_value = ATOMIC64_INIT(0);
+ 
++void pvclock_resume(void)
++{
++	atomic64_set(&last_value, 0);
++}
++
+ cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
+ {
+ 	struct pvclock_shadow_time shadow;
+diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
+index b2bb5aa..5da5e53 100644
+--- a/arch/x86/xen/time.c
++++ b/arch/x86/xen/time.c
+@@ -426,6 +426,8 @@ void xen_timer_resume(void)
+ {
+ 	int cpu;
+ 
++	pvclock_resume();
++
+ 	if (xen_clockevent != &xen_vcpuop_clockevent)
+ 		return;

pkgs/top-level/all-packages.nix

@@ -4582,7 +4582,7 @@ let
         kernelPatches.cifs_timeout
         kernelPatches.no_xsave
         kernelPatches.dell_rfkill
-        kernelPatches.revert_pvclock_sync
+        kernelPatches.xen_pvclock_resume
       ];
   };