s390/nmi: disable interrupts on extended save area update

Updating of the pointer to machine check extended save area
on the IPL CPU needs the lowcore protection to be disabled.
Disable interrupts while the protection is off to avoid
unnoticed writes to the lowcore.

Suggested-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

3 files changed, 26 insertions, 30 deletions

diff --git a/arch/s390/kernel/nmi.c b/arch/s390/kernel/nmi.c
index 3f18c1412eba..1cf1e37553e8 100644
--- a/arch/s390/kernel/nmi.c
+++ b/arch/s390/kernel/nmi.c
@@ -58,27 +58,27 @@ static inline unsigned long nmi_get_mcesa_size(void)
 
 /*
  * The initial machine check extended save area for the boot CPU.
- * It will be replaced by nmi_init() with an allocated structure.
- * The structure is required for machine check happening early in
- * the boot process.
+ * It will be replaced on the boot CPU reinit with an allocated
+ * structure. The structure is required for machine check happening
+ * early in the boot process.
  */
 static struct mcesa boot_mcesa __initdata __aligned(MCESA_MAX_SIZE);
 
-void __init nmi_alloc_boot_cpu(struct lowcore *lc)
+void __init nmi_alloc_mcesa_early(u64 *mcesad)
 {
 	if (!nmi_needs_mcesa())
 		return;
-	lc->mcesad = __pa(&boot_mcesa);
+	*mcesad = __pa(&boot_mcesa);
 	if (MACHINE_HAS_GS)
-		lc->mcesad |= ilog2(MCESA_MAX_SIZE);
+		*mcesad |= ilog2(MCESA_MAX_SIZE);
 }
 
-static int __init nmi_init(void)
+static void __init nmi_alloc_cache(void)
 {
-	unsigned long origin, cr0, size;
+	unsigned long size;
 
 	if (!nmi_needs_mcesa())
-		return 0;
+		return;
 	size = nmi_get_mcesa_size();
 	if (size > MCESA_MIN_SIZE)
 		mcesa_origin_lc = ilog2(size);
@@ -86,40 +86,31 @@ static int __init nmi_init(void)
 	mcesa_cache = kmem_cache_create("nmi_save_areas", size, size, 0, NULL);
 	if (!mcesa_cache)
 		panic("Couldn't create nmi save area cache");
-	origin = (unsigned long) kmem_cache_alloc(mcesa_cache, GFP_KERNEL);
-	if (!origin)
-		panic("Couldn't allocate nmi save area");
-	/* The pointer is stored with mcesa_bits ORed in */
-	kmemleak_not_leak((void *) origin);
-	__ctl_store(cr0, 0, 0);
-	__ctl_clear_bit(0, 28); /* disable lowcore protection */
-	/* Replace boot_mcesa on the boot CPU */
-	S390_lowcore.mcesad = __pa(origin) | mcesa_origin_lc;
-	__ctl_load(cr0, 0, 0);
-	return 0;
 }
-early_initcall(nmi_init);
 
-int nmi_alloc_per_cpu(struct lowcore *lc)
+int __ref nmi_alloc_mcesa(u64 *mcesad)
 {
 	unsigned long origin;
 
+	*mcesad = 0;
 	if (!nmi_needs_mcesa())
 		return 0;
+	if (!mcesa_cache)
+		nmi_alloc_cache();
 	origin = (unsigned long) kmem_cache_alloc(mcesa_cache, GFP_KERNEL);
 	if (!origin)
 		return -ENOMEM;
 	/* The pointer is stored with mcesa_bits ORed in */
 	kmemleak_not_leak((void *) origin);
-	lc->mcesad = __pa(origin) | mcesa_origin_lc;
+	*mcesad = __pa(origin) | mcesa_origin_lc;
 	return 0;
 }
 
-void nmi_free_per_cpu(struct lowcore *lc)
+void nmi_free_mcesa(u64 *mcesad)
 {
 	if (!nmi_needs_mcesa())
 		return;
-	kmem_cache_free(mcesa_cache, __va(lc->mcesad & MCESA_ORIGIN_MASK));
+	kmem_cache_free(mcesa_cache, __va(*mcesad & MCESA_ORIGIN_MASK));
 }
 
 static notrace void s390_handle_damage(void)
diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
index 225ab2d0a4c6..f2c25d113e7b 100644
--- a/arch/s390/kernel/setup.c
+++ b/arch/s390/kernel/setup.c
@@ -445,7 +445,7 @@ static void __init setup_lowcore_dat_off(void)
 	lc->lpp = LPP_MAGIC;
 	lc->machine_flags = S390_lowcore.machine_flags;
 	lc->preempt_count = S390_lowcore.preempt_count;
-	nmi_alloc_boot_cpu(lc);
+	nmi_alloc_mcesa_early(&lc->mcesad);
 	lc->sys_enter_timer = S390_lowcore.sys_enter_timer;
 	lc->exit_timer = S390_lowcore.exit_timer;
 	lc->user_timer = S390_lowcore.user_timer;
diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
index 2590c31a8fc3..1172aaf0b7e2 100644
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -212,7 +212,7 @@ static int pcpu_alloc_lowcore(struct pcpu *pcpu, int cpu)
 	lc->return_lpswe = gen_lpswe(__LC_RETURN_PSW);
 	lc->return_mcck_lpswe = gen_lpswe(__LC_RETURN_MCCK_PSW);
 	lc->preempt_count = PREEMPT_DISABLED;
-	if (nmi_alloc_per_cpu(lc))
+	if (nmi_alloc_mcesa(&lc->mcesad))
 		goto out;
 	lowcore_ptr[cpu] = lc;
 	pcpu_sigp_retry(pcpu, SIGP_SET_PREFIX, (u32)(unsigned long) lc);
@@ -239,7 +239,7 @@ static void pcpu_free_lowcore(struct pcpu *pcpu)
 	mcck_stack = lc->mcck_stack - STACK_INIT_OFFSET;
 	pcpu_sigp_retry(pcpu, SIGP_SET_PREFIX, 0);
 	lowcore_ptr[cpu] = NULL;
-	nmi_free_per_cpu(lc);
+	nmi_free_mcesa(&lc->mcesad);
 	stack_free(async_stack);
 	stack_free(mcck_stack);
 	free_pages(nodat_stack, THREAD_SIZE_ORDER);
@@ -1271,14 +1271,15 @@ static int __init smp_reinit_ipl_cpu(void)
 {
 	unsigned long async_stack, nodat_stack, mcck_stack;
 	struct lowcore *lc, *lc_ipl;
-	unsigned long flags;
+	unsigned long flags, cr0;
+	u64 mcesad;
 
 	lc_ipl = lowcore_ptr[0];
 	lc = (struct lowcore *)	__get_free_pages(GFP_KERNEL | GFP_DMA, LC_ORDER);
 	nodat_stack = __get_free_pages(GFP_KERNEL, THREAD_SIZE_ORDER);
 	async_stack = stack_alloc();
 	mcck_stack = stack_alloc();
-	if (!lc || !nodat_stack || !async_stack || !mcck_stack)
+	if (!lc || !nodat_stack || !async_stack || !mcck_stack || nmi_alloc_mcesa(&mcesad))
 		panic("Couldn't allocate memory");
 
 	local_irq_save(flags);
@@ -1287,6 +1288,10 @@ static int __init smp_reinit_ipl_cpu(void)
 	S390_lowcore.nodat_stack = nodat_stack + STACK_INIT_OFFSET;
 	S390_lowcore.async_stack = async_stack + STACK_INIT_OFFSET;
 	S390_lowcore.mcck_stack = mcck_stack + STACK_INIT_OFFSET;
+	__ctl_store(cr0, 0, 0);
+	__ctl_clear_bit(0, 28); /* disable lowcore protection */
+	S390_lowcore.mcesad = mcesad;
+	__ctl_load(cr0, 0, 0);
 	lowcore_ptr[0] = lc;
 	local_mcck_enable();
 	local_irq_restore(flags);