From: Kevin Monroe <kmonroe@redhat.com>
Date: Tue, 10 Nov 2009 23:04:09 -0500
Subject: [powerpc] fix to handle SLB resize during migration
Message-id: <4AF9F169.6060507@redhat.com>
Patchwork-id: 21358
O-Subject: Re: [PATCH RHEL5.5 BZ524112] Fix to handle SLB resize during migration
Bugzilla: 524112
RH-Acked-by: David Howells <dhowells@redhat.com>

On 10/09/2009 03:02 PM, Kevin Monroe wrote:
RHBZ#:
======
https://bugzilla.redhat.com/show_bug.cgi?id=524112

Description:
============
The SLB can change sizes across a live migration, which was not
being handled, resulting in possible machine crashes during
migration if migrating to a machine which has a smaller max SLB
size than the source machine. Fix this by first reducing the
SLB size to the minimum possible value, which is 32, prior to
migration. Then during the device tree update which occurs after
migration, we make the call to ensure the SLB gets updated. Also
add the slb_size to the lparcfg output so that the migration
tools can check to make sure the kernel has this capability
before allowing migration in scenarios where the SLB size will change.

RHEL Version Found:
===================
RHEL 5.4

kABI Status:
============
No symbols were harmed.

Brew:
=====
Built on all platforms.
https://brewweb.devel.redhat.com/taskinfo?taskID=2023948

Upstream Status:
================
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=46db2f86a3b2a94e0b33e0b4548fb7b7b6bdff66

Test Status:
============
To recreate the problem, simply attempt to live migrate an LPAR between
machines with different max SLB sizes several times.

With this patch, I have been able to successfully migrate between
machines with different SLB sizes.

diff --git a/arch/powerpc/kernel/lparcfg.c b/arch/powerpc/kernel/lparcfg.c
index 23f34da..e98d22c 100644
--- a/arch/powerpc/kernel/lparcfg.c
+++ b/arch/powerpc/kernel/lparcfg.c
@@ -35,6 +35,7 @@
 #include <asm/iseries/it_exp_vpd_panel.h>
 #include <asm/prom.h>
 #include <asm/vdso_datapage.h>
+#include <asm/mmu.h>
 
 #define MODULE_VERS "1.7"
 #define MODULE_NAME "lparcfg"
@@ -403,6 +404,8 @@ static int pseries_lparcfg_data(struct seq_file *m, void *v)
 
 	seq_printf(m, "shared_processor_mode=%d\n", lppaca[0].shared_proc);
 
+	seq_printf(m, "slb_size=%d\n", mmu_slb_size);
+
 	return 0;
 }
 
diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
index a980907..e97f516 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -38,6 +38,7 @@
 #include <asm/udbg.h>
 #include <asm/syscalls.h>
 #include <asm/atomic.h>
+#include <asm/mmu.h>
 
 struct rtas_t rtas = {
 	.lock = SPIN_LOCK_UNLOCKED
@@ -689,6 +690,7 @@ static void rtas_percpu_suspend_me(void *info)
 		goto out;
 
 	if (rc == H_CONTINUE) {
+		slb_set_size(SLB_MIN_SIZE);
 		printk("Linux suspends from hypervisor at %lld "
 		       "(cpu %u (hwid%u)).\n", sched_clock(),
 		       smp_processor_id(), hard_smp_processor_id());
diff --git a/arch/powerpc/mm/slb.c b/arch/powerpc/mm/slb.c
index 046fc7a..227b677 100644
--- a/arch/powerpc/mm/slb.c
+++ b/arch/powerpc/mm/slb.c
@@ -31,6 +31,8 @@
 #define DBG(fmt...)
 #endif
 
+extern unsigned int *slb_compare_rr_to_size;
+
 extern void slb_allocate_realmode(unsigned long ea);
 extern void slb_allocate_user(unsigned long ea);
 
@@ -195,21 +197,26 @@ void switch_slb(struct task_struct *tsk, struct mm_struct *mm)
 static inline void patch_slb_encoding(unsigned int *insn_addr,
 				      unsigned int immed)
 {
-	/* Assume the instruction had a "0" immediate value, just
-	 * "or" in the new value
-	 */
-	*insn_addr |= immed;
+	*insn_addr = (*insn_addr & 0xffff0000) | immed;
 	flush_icache_range((unsigned long)insn_addr, 4+
 			   (unsigned long)insn_addr);
 }
 
+void slb_set_size(u16 size)
+{
+	if (mmu_slb_size == size)
+		return;
+
+	mmu_slb_size = size;
+	patch_slb_encoding(slb_compare_rr_to_size, mmu_slb_size);
+}
+
 void slb_initialize(void)
 {
 	unsigned long linear_llp, vmalloc_llp, io_llp;
 	static int slb_encoding_inited;
 	extern unsigned int *slb_miss_kernel_load_linear;
 	extern unsigned int *slb_miss_kernel_load_io;
-	extern unsigned int *slb_compare_rr_to_size;
 #ifdef CONFIG_HUGETLB_PAGE
 	extern unsigned int *slb_miss_user_load_huge;
 	unsigned long huge_llp;
diff --git a/arch/powerpc/platforms/pseries/reconfig.c b/arch/powerpc/platforms/pseries/reconfig.c
index 1773103..f92b241 100644
--- a/arch/powerpc/platforms/pseries/reconfig.c
+++ b/arch/powerpc/platforms/pseries/reconfig.c
@@ -20,6 +20,7 @@
 #include <asm/machdep.h>
 #include <asm/uaccess.h>
 #include <asm/pSeries_reconfig.h>
+#include <asm/mmu.h>
 
 
 
@@ -438,9 +439,15 @@ static int do_update_property(char *buf, size_t bufsize)
 	if (!newprop)
 		return -ENOMEM;
 
+	if (!strcmp(name, "slb-size") || !strcmp(name, "ibm,slb-size"))
+		slb_set_size(*(unsigned int *)value);
+
 	oldprop = of_find_property(np, name,NULL);
-	if (!oldprop)
+	if (!oldprop) {
+		if (strlen(name))
+			return prom_add_property(np, newprop);
 		return -ENODEV;
+	}
 
 	return prom_update_property(np, newprop, oldprop);
 }
diff --git a/include/asm-powerpc/mmu.h b/include/asm-powerpc/mmu.h
index e9063b3..fc0bfeb 100644
--- a/include/asm-powerpc/mmu.h
+++ b/include/asm-powerpc/mmu.h
@@ -47,6 +47,7 @@ extern char initial_stab[];
 
 #define SLB_NUM_BOLTED		3
 #define SLB_CACHE_ENTRIES	8
+#define SLB_MIN_SIZE		32
 
 /* Bits in the SLB ESID word */
 #define SLB_ESID_V		ASM_CONST(0x0000000008000000) /* valid */
@@ -286,6 +287,7 @@ extern void stabs_alloc(void);
 extern void slb_initialize(void);
 extern void slb_flush_and_rebolt(void);
 extern void stab_initialize(unsigned long stab);
+extern void slb_set_size(u16 size);
 
 extern void slb_vmalloc_update(void);
 #endif /* __ASSEMBLY__ */