Revert "s390/smp: rework absolute lowcore access"

This reverts commit 7d06fed77b7d8fc9f6cc41b4e3f2823d32532ad8.

This introduced vmem_mutex locking from vmem_map_4k_page()
function called from smp_reinit_ipl_cpu() with interrupts
disabled. While it is a pre-SMP early initcall no other CPUs
running in parallel nor other code taking vmem_mutex on this
boot stage - it still needs to be fixed.

Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

1 files changed, 37 insertions, 30 deletions

diff --git a/arch/s390/mm/maccess.c b/arch/s390/mm/maccess.c
index b8451ddbb3d6..d6d84e02f35a 100644
--- a/arch/s390/mm/maccess.c
+++ b/arch/s390/mm/maccess.c
@@ -15,7 +15,6 @@
 #include <asm/asm-extable.h>
 #include <asm/ctl_reg.h>
 #include <asm/io.h>
-#include <asm/abs_lowcore.h>
 #include <asm/stacktrace.h>
 
 static notrace long s390_kernel_write_odd(void *dst, const void *src, size_t size)
@@ -149,20 +148,46 @@ int memcpy_real(void *dest, unsigned long src, size_t count)
 }
 
 /*
- * Find CPU that owns swapped prefix page
+ * Copy memory in absolute mode (kernel to kernel)
  */
-static int get_swapped_owner(phys_addr_t addr)
+void memcpy_absolute(void *dest, void *src, size_t count)
+{
+	unsigned long cr0, flags, prefix;
+
+	flags = arch_local_irq_save();
+	__ctl_store(cr0, 0, 0);
+	__ctl_clear_bit(0, 28); /* disable lowcore protection */
+	prefix = store_prefix();
+	if (prefix) {
+		local_mcck_disable();
+		set_prefix(0);
+		memcpy(dest, src, count);
+		set_prefix(prefix);
+		local_mcck_enable();
+	} else {
+		memcpy(dest, src, count);
+	}
+	__ctl_load(cr0, 0, 0);
+	arch_local_irq_restore(flags);
+}
+
+/*
+ * Check if physical address is within prefix or zero page
+ */
+static int is_swapped(phys_addr_t addr)
 {
 	phys_addr_t lc;
 	int cpu;
 
+	if (addr < sizeof(struct lowcore))
+		return 1;
 	for_each_online_cpu(cpu) {
 		lc = virt_to_phys(lowcore_ptr[cpu]);
 		if (addr > lc + sizeof(struct lowcore) - 1 || addr < lc)
 			continue;
-		return cpu;
+		return 1;
 	}
-	return -1;
+	return 0;
 }
 
 /*
@@ -175,35 +200,17 @@ void *xlate_dev_mem_ptr(phys_addr_t addr)
 {
 	void *ptr = phys_to_virt(addr);
 	void *bounce = ptr;
-	struct lowcore *abs_lc;
-	unsigned long flags;
 	unsigned long size;
-	int this_cpu, cpu;
 
 	cpus_read_lock();
-	this_cpu = get_cpu();
-	if (addr >= sizeof(struct lowcore)) {
-		cpu = get_swapped_owner(addr);
-		if (cpu < 0)
-			goto out;
-	}
-	bounce = (void *)__get_free_page(GFP_ATOMIC);
-	if (!bounce)
-		goto out;
-	size = PAGE_SIZE - (addr & ~PAGE_MASK);
-	if (addr < sizeof(struct lowcore)) {
-		abs_lc = get_abs_lowcore(&flags);
-		ptr = (void *)abs_lc + addr;
-		memcpy(bounce, ptr, size);
-		put_abs_lowcore(abs_lc, flags);
-	} else if (cpu == this_cpu) {
-		ptr = (void *)(addr - virt_to_phys(lowcore_ptr[cpu]));
-		memcpy(bounce, ptr, size);
-	} else {
-		memcpy(bounce, ptr, size);
+	preempt_disable();
+	if (is_swapped(addr)) {
+		size = PAGE_SIZE - (addr & ~PAGE_MASK);
+		bounce = (void *) __get_free_page(GFP_ATOMIC);
+		if (bounce)
+			memcpy_absolute(bounce, ptr, size);
 	}
-out:
-	put_cpu();
+	preempt_enable();
 	cpus_read_unlock();
 	return bounce;
 }