14 files changed, 315 insertions, 84 deletions

diff --git a/arch/s390/boot/startup.c b/arch/s390/boot/startup.c
index bc48fe82d949..41b7af7a9365 100644
--- a/arch/s390/boot/startup.c
+++ b/arch/s390/boot/startup.c
@@ -10,11 +10,13 @@
 #include <asm/sclp.h>
 #include <asm/diag.h>
 #include <asm/uv.h>
+#include <asm/abs_lowcore.h>
 #include "decompressor.h"
 #include "boot.h"
 #include "uv.h"
 
 unsigned long __bootdata_preserved(__kaslr_offset);
+unsigned long __bootdata_preserved(__abs_lowcore);
 unsigned long __bootdata(__amode31_base);
 unsigned long __bootdata_preserved(VMALLOC_START);
 unsigned long __bootdata_preserved(VMALLOC_END);
@@ -180,7 +182,8 @@ static void setup_kernel_memory_layout(void)
 	/* force vmalloc and modules below kasan shadow */
 	vmax = min(vmax, KASAN_SHADOW_START);
 #endif
-	MODULES_END = vmax;
+	__abs_lowcore = round_down(vmax - ABS_LOWCORE_MAP_SIZE, sizeof(struct lowcore));
+	MODULES_END = round_down(__abs_lowcore, _SEGMENT_SIZE);
 	MODULES_VADDR = MODULES_END - MODULES_LEN;
 	VMALLOC_END = MODULES_VADDR;
 
diff --git a/arch/s390/include/asm/abs_lowcore.h b/arch/s390/include/asm/abs_lowcore.h
new file mode 100644
index 000000000000..4c61b14ee928
--- /dev/null
+++ b/arch/s390/include/asm/abs_lowcore.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_S390_ABS_LOWCORE_H
+#define _ASM_S390_ABS_LOWCORE_H
+
+#include <asm/lowcore.h>
+
+#define ABS_LOWCORE_MAP_SIZE	(NR_CPUS * sizeof(struct lowcore))
+
+extern unsigned long __abs_lowcore;
+extern bool abs_lowcore_mapped;
+
+struct lowcore *get_abs_lowcore(unsigned long *flags);
+void put_abs_lowcore(struct lowcore *lc, unsigned long flags);
+int abs_lowcore_map(int cpu, struct lowcore *lc, bool alloc);
+void abs_lowcore_unmap(int cpu);
+
+#endif /* _ASM_S390_ABS_LOWCORE_H */
diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index f019df19884d..45617c966202 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -1777,6 +1777,9 @@ static inline swp_entry_t __swp_entry(unsigned long type, unsigned long offset)
 
 extern int vmem_add_mapping(unsigned long start, unsigned long size);
 extern void vmem_remove_mapping(unsigned long start, unsigned long size);
+extern int __vmem_map_4k_page(unsigned long addr, unsigned long phys, pgprot_t prot, bool alloc);
+extern int vmem_map_4k_page(unsigned long addr, unsigned long phys, pgprot_t prot);
+extern void vmem_unmap_4k_page(unsigned long addr);
 extern int s390_enable_sie(void);
 extern int s390_enable_skey(void);
 extern void s390_reset_cmma(struct mm_struct *mm);
diff --git a/arch/s390/include/asm/processor.h b/arch/s390/include/asm/processor.h
index bd66f8e34949..93677ae89e7e 100644
--- a/arch/s390/include/asm/processor.h
+++ b/arch/s390/include/asm/processor.h
@@ -307,21 +307,6 @@ static __always_inline void __noreturn disabled_wait(void)
 #define ARCH_LOW_ADDRESS_LIMIT	0x7fffffffUL
 
 extern int memcpy_real(void *, unsigned long, size_t);
-extern void memcpy_absolute(void *, void *, size_t);
-
-#define put_abs_lowcore(member, x) do {					\
-	unsigned long __abs_address = offsetof(struct lowcore, member);	\
-	__typeof__(((struct lowcore *)0)->member) __tmp = (x);		\
-									\
-	memcpy_absolute(__va(__abs_address), &__tmp, sizeof(__tmp));	\
-} while (0)
-
-#define get_abs_lowcore(x, member) do {					\
-	unsigned long __abs_address = offsetof(struct lowcore, member);	\
-	__typeof__(((struct lowcore *)0)->member) *__ptr = &(x);	\
-									\
-	memcpy_absolute(__ptr, __va(__abs_address), sizeof(*__ptr));	\
-} while (0)
 
 extern int s390_isolate_bp(void);
 extern int s390_isolate_bp_guest(void);
diff --git a/arch/s390/kernel/Makefile b/arch/s390/kernel/Makefile
index 3cbfa9fddd9a..45e4b2f41e05 100644
--- a/arch/s390/kernel/Makefile
+++ b/arch/s390/kernel/Makefile
@@ -40,7 +40,7 @@ obj-y	+= sysinfo.o lgr.o os_info.o machine_kexec.o
 obj-y	+= runtime_instr.o cache.o fpu.o dumpstack.o guarded_storage.o sthyi.o
 obj-y	+= entry.o reipl.o relocate_kernel.o kdebugfs.o alternative.o
 obj-y	+= nospec-branch.o ipl_vmparm.o machine_kexec_reloc.o unwind_bc.o
-obj-y	+= smp.o text_amode31.o stacktrace.o
+obj-y	+= smp.o text_amode31.o stacktrace.o abs_lowcore.o
 
 extra-y				+= head64.o vmlinux.lds
 
diff --git a/arch/s390/kernel/abs_lowcore.c b/arch/s390/kernel/abs_lowcore.c
new file mode 100644
index 000000000000..fb92e8ed0525
--- /dev/null
+++ b/arch/s390/kernel/abs_lowcore.c
@@ -0,0 +1,95 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/pgtable.h>
+#include <asm/abs_lowcore.h>
+
+#define ABS_LOWCORE_UNMAPPED	1
+#define ABS_LOWCORE_LAP_ON	2
+#define ABS_LOWCORE_IRQS_ON	4
+
+unsigned long __bootdata_preserved(__abs_lowcore);
+bool __ro_after_init abs_lowcore_mapped;
+
+int abs_lowcore_map(int cpu, struct lowcore *lc, bool alloc)
+{
+	unsigned long addr = __abs_lowcore + (cpu * sizeof(struct lowcore));
+	unsigned long phys = __pa(lc);
+	int rc, i;
+
+	for (i = 0; i < LC_PAGES; i++) {
+		rc = __vmem_map_4k_page(addr, phys, PAGE_KERNEL, alloc);
+		if (rc) {
+			/*
+			 * Do not unmap allocated page tables in case the
+			 * allocation was not requested. In such a case the
+			 * request is expected coming from an atomic context,
+			 * while the unmap attempt might sleep.
+			 */
+			if (alloc) {
+				for (--i; i >= 0; i--) {
+					addr -= PAGE_SIZE;
+					vmem_unmap_4k_page(addr);
+				}
+			}
+			return rc;
+		}
+		addr += PAGE_SIZE;
+		phys += PAGE_SIZE;
+	}
+	return 0;
+}
+
+void abs_lowcore_unmap(int cpu)
+{
+	unsigned long addr = __abs_lowcore + (cpu * sizeof(struct lowcore));
+	int i;
+
+	for (i = 0; i < LC_PAGES; i++) {
+		vmem_unmap_4k_page(addr);
+		addr += PAGE_SIZE;
+	}
+}
+
+struct lowcore *get_abs_lowcore(unsigned long *flags)
+{
+	unsigned long irq_flags;
+	union ctlreg0 cr0;
+	int cpu;
+
+	*flags = 0;
+	cpu = get_cpu();
+	if (abs_lowcore_mapped) {
+		return ((struct lowcore *)__abs_lowcore) + cpu;
+	} else {
+		if (cpu != 0)
+			panic("Invalid unmapped absolute lowcore access\n");
+		local_irq_save(irq_flags);
+		if (!irqs_disabled_flags(irq_flags))
+			*flags |= ABS_LOWCORE_IRQS_ON;
+		__ctl_store(cr0.val, 0, 0);
+		if (cr0.lap) {
+			*flags |= ABS_LOWCORE_LAP_ON;
+			__ctl_clear_bit(0, 28);
+		}
+		*flags |= ABS_LOWCORE_UNMAPPED;
+		return lowcore_ptr[0];
+	}
+}
+
+void put_abs_lowcore(struct lowcore *lc, unsigned long flags)
+{
+	if (abs_lowcore_mapped) {
+		if (flags)
+			panic("Invalid mapped absolute lowcore release\n");
+	} else {
+		if (smp_processor_id() != 0)
+			panic("Invalid mapped absolute lowcore access\n");
+		if (!(flags & ABS_LOWCORE_UNMAPPED))
+			panic("Invalid unmapped absolute lowcore release\n");
+		if (flags & ABS_LOWCORE_LAP_ON)
+			__ctl_set_bit(0, 28);
+		if (flags & ABS_LOWCORE_IRQS_ON)
+			local_irq_enable();
+	}
+	put_cpu();
+}
diff --git a/arch/s390/kernel/ipl.c b/arch/s390/kernel/ipl.c
index 1cc85b8ff42e..325cbf69ebbd 100644
--- a/arch/s390/kernel/ipl.c
+++ b/arch/s390/kernel/ipl.c
@@ -29,6 +29,7 @@
 #include <asm/sclp.h>
 #include <asm/checksum.h>
 #include <asm/debug.h>
+#include <asm/abs_lowcore.h>
 #include <asm/os_info.h>
 #include <asm/sections.h>
 #include <asm/boot_data.h>
@@ -1642,12 +1643,16 @@ static struct shutdown_action __refdata dump_action = {
 static void dump_reipl_run(struct shutdown_trigger *trigger)
 {
 	unsigned long ipib = (unsigned long) reipl_block_actual;
+	struct lowcore *abs_lc;
+	unsigned long flags;
 	unsigned int csum;
 
 	csum = (__force unsigned int)
 	       csum_partial(reipl_block_actual, reipl_block_actual->hdr.len, 0);
-	put_abs_lowcore(ipib, ipib);
-	put_abs_lowcore(ipib_checksum, csum);
+	abs_lc = get_abs_lowcore(&flags);
+	abs_lc->ipib = ipib;
+	abs_lc->ipib_checksum = csum;
+	put_abs_lowcore(abs_lc, flags);
 	dump_run(trigger);
 }
 
diff --git a/arch/s390/kernel/machine_kexec.c b/arch/s390/kernel/machine_kexec.c
index ab761c008f98..4579b42286d5 100644
--- a/arch/s390/kernel/machine_kexec.c
+++ b/arch/s390/kernel/machine_kexec.c
@@ -21,6 +21,7 @@
 #include <asm/elf.h>
 #include <asm/asm-offsets.h>
 #include <asm/cacheflush.h>
+#include <asm/abs_lowcore.h>
 #include <asm/os_info.h>
 #include <asm/set_memory.h>
 #include <asm/stacktrace.h>
@@ -222,13 +223,18 @@ void machine_kexec_cleanup(struct kimage *image)
 
 void arch_crash_save_vmcoreinfo(void)
 {
+	struct lowcore *abs_lc;
+	unsigned long flags;
+
 	VMCOREINFO_SYMBOL(lowcore_ptr);
 	VMCOREINFO_SYMBOL(high_memory);
 	VMCOREINFO_LENGTH(lowcore_ptr, NR_CPUS);
 	vmcoreinfo_append_str("SAMODE31=%lx\n", __samode31);
 	vmcoreinfo_append_str("EAMODE31=%lx\n", __eamode31);
 	vmcoreinfo_append_str("KERNELOFFSET=%lx\n", kaslr_offset());
-	put_abs_lowcore(vmcore_info, paddr_vmcoreinfo_note());
+	abs_lc = get_abs_lowcore(&flags);
+	abs_lc->vmcore_info = paddr_vmcoreinfo_note();
+	put_abs_lowcore(abs_lc, flags);
 }
 
 void machine_shutdown(void)
diff --git a/arch/s390/kernel/os_info.c b/arch/s390/kernel/os_info.c
index 1acc2e05d70f..506ccb74d2d0 100644
--- a/arch/s390/kernel/os_info.c
+++ b/arch/s390/kernel/os_info.c
@@ -13,7 +13,7 @@
 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <asm/checksum.h>
-#include <asm/lowcore.h>
+#include <asm/abs_lowcore.h>
 #include <asm/os_info.h>
 #include <asm/asm-offsets.h>
 
@@ -57,13 +57,16 @@ void os_info_entry_add(int nr, void *ptr, u64 size)
  */
 void __init os_info_init(void)
 {
-	void *ptr = &os_info;
+	struct lowcore *abs_lc;
+	unsigned long flags;
 
 	os_info.version_major = OS_INFO_VERSION_MAJOR;
 	os_info.version_minor = OS_INFO_VERSION_MINOR;
 	os_info.magic = OS_INFO_MAGIC;
 	os_info.csum = os_info_csum(&os_info);
-	put_abs_lowcore(os_info, __pa(ptr));
+	abs_lc = get_abs_lowcore(&flags);
+	abs_lc->os_info = __pa(&os_info);
+	put_abs_lowcore(abs_lc, flags);
 }
 
 #ifdef CONFIG_CRASH_DUMP
diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
index 063f0512a64a..8d0a670c9f48 100644
--- a/arch/s390/kernel/setup.c
+++ b/arch/s390/kernel/setup.c
@@ -58,7 +58,7 @@
 #include <asm/smp.h>
 #include <asm/mmu_context.h>
 #include <asm/cpcmd.h>
-#include <asm/lowcore.h>
+#include <asm/abs_lowcore.h>
 #include <asm/nmi.h>
 #include <asm/irq.h>
 #include <asm/page.h>
@@ -412,8 +412,9 @@ void __init arch_call_rest_init(void)
 static void __init setup_lowcore_dat_off(void)
 {
 	unsigned long int_psw_mask = PSW_KERNEL_BITS;
+	struct lowcore *abs_lc, *lc;
 	unsigned long mcck_stack;
-	struct lowcore *lc;
+	unsigned long flags;
 
 	if (IS_ENABLED(CONFIG_KASAN))
 		int_psw_mask |= PSW_MASK_DAT;
@@ -475,12 +476,14 @@ static void __init setup_lowcore_dat_off(void)
 	lc->restart_data = 0;
 	lc->restart_source = -1U;
 
-	put_abs_lowcore(restart_stack, lc->restart_stack);
-	put_abs_lowcore(restart_fn, lc->restart_fn);
-	put_abs_lowcore(restart_data, lc->restart_data);
-	put_abs_lowcore(restart_source, lc->restart_source);
-	put_abs_lowcore(restart_psw, lc->restart_psw);
-	put_abs_lowcore(mcesad, lc->mcesad);
+	abs_lc = get_abs_lowcore(&flags);
+	abs_lc->restart_stack = lc->restart_stack;
+	abs_lc->restart_fn = lc->restart_fn;
+	abs_lc->restart_data = lc->restart_data;
+	abs_lc->restart_source = lc->restart_source;
+	abs_lc->restart_psw = lc->restart_psw;
+	abs_lc->mcesad = lc->mcesad;
+	put_abs_lowcore(abs_lc, flags);
 
 	mcck_stack = (unsigned long)memblock_alloc(THREAD_SIZE, THREAD_SIZE);
 	if (!mcck_stack)
@@ -501,8 +504,8 @@ static void __init setup_lowcore_dat_off(void)
 
 static void __init setup_lowcore_dat_on(void)
 {
-	struct lowcore *lc = lowcore_ptr[0];
-	int cr;
+	struct lowcore *abs_lc;
+	unsigned long flags;
 
 	__ctl_clear_bit(0, 28);
 	S390_lowcore.external_new_psw.mask |= PSW_MASK_DAT;
@@ -511,10 +514,15 @@ static void __init setup_lowcore_dat_on(void)
 	S390_lowcore.io_new_psw.mask |= PSW_MASK_DAT;
 	__ctl_set_bit(0, 28);
 	__ctl_store(S390_lowcore.cregs_save_area, 0, 15);
-	put_abs_lowcore(restart_flags, RESTART_FLAG_CTLREGS);
-	put_abs_lowcore(program_new_psw, lc->program_new_psw);
-	for (cr = 0; cr < ARRAY_SIZE(lc->cregs_save_area); cr++)
-		put_abs_lowcore(cregs_save_area[cr], lc->cregs_save_area[cr]);
+	if (abs_lowcore_map(0, lowcore_ptr[0], true))
+		panic("Couldn't setup absolute lowcore");
+	abs_lowcore_mapped = true;
+	abs_lc = get_abs_lowcore(&flags);
+	abs_lc->restart_flags = RESTART_FLAG_CTLREGS;
+	abs_lc->program_new_psw = S390_lowcore.program_new_psw;
+	memcpy(abs_lc->cregs_save_area, S390_lowcore.cregs_save_area,
+	       sizeof(abs_lc->cregs_save_area));
+	put_abs_lowcore(abs_lc, flags);
 }
 
 static struct resource code_resource = {
diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
index 0e8e5546933f..0f646b568d59 100644
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -45,7 +45,7 @@
 #include <asm/irq.h>
 #include <asm/tlbflush.h>
 #include <asm/vtimer.h>
-#include <asm/lowcore.h>
+#include <asm/abs_lowcore.h>
 #include <asm/sclp.h>
 #include <asm/debug.h>
 #include <asm/os_info.h>
@@ -212,10 +212,14 @@ static int pcpu_alloc_lowcore(struct pcpu *pcpu, int cpu)
 	lc->preempt_count = PREEMPT_DISABLED;
 	if (nmi_alloc_mcesa(&lc->mcesad))
 		goto out;
+	if (abs_lowcore_map(cpu, lc, true))
+		goto out_mcesa;
 	lowcore_ptr[cpu] = lc;
 	pcpu_sigp_retry(pcpu, SIGP_SET_PREFIX, __pa(lc));
 	return 0;
 
+out_mcesa:
+	nmi_free_mcesa(&lc->mcesad);
 out:
 	stack_free(mcck_stack);
 	stack_free(async_stack);
@@ -237,6 +241,7 @@ 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;
+	abs_lowcore_unmap(cpu);
 	nmi_free_mcesa(&lc->mcesad);
 	stack_free(async_stack);
 	stack_free(mcck_stack);
@@ -315,9 +320,12 @@ static void pcpu_delegate(struct pcpu *pcpu,
 			  pcpu_delegate_fn *func,
 			  void *data, unsigned long stack)
 {
-	struct lowcore *lc = lowcore_ptr[pcpu - pcpu_devices];
-	unsigned int source_cpu = stap();
+	struct lowcore *lc, *abs_lc;
+	unsigned int source_cpu;
+	unsigned long flags;
 
+	lc = lowcore_ptr[pcpu - pcpu_devices];
+	source_cpu = stap();
 	__load_psw_mask(PSW_KERNEL_BITS | PSW_MASK_DAT);
 	if (pcpu->address == source_cpu) {
 		call_on_stack(2, stack, void, __pcpu_delegate,
@@ -332,10 +340,12 @@ static void pcpu_delegate(struct pcpu *pcpu,
 		lc->restart_data = (unsigned long)data;
 		lc->restart_source = source_cpu;
 	} else {
-		put_abs_lowcore(restart_stack, stack);
-		put_abs_lowcore(restart_fn, (unsigned long)func);
-		put_abs_lowcore(restart_data, (unsigned long)data);
-		put_abs_lowcore(restart_source, source_cpu);
+		abs_lc = get_abs_lowcore(&flags);
+		abs_lc->restart_stack = stack;
+		abs_lc->restart_fn = (unsigned long)func;
+		abs_lc->restart_data = (unsigned long)data;
+		abs_lc->restart_source = source_cpu;
+		put_abs_lowcore(abs_lc, flags);
 	}
 	__bpon();
 	asm volatile(
@@ -581,6 +591,8 @@ static DEFINE_SPINLOCK(ctl_lock);
 void smp_ctl_set_clear_bit(int cr, int bit, bool set)
 {
 	struct ec_creg_mask_parms parms = { .cr = cr, };
+	struct lowcore *abs_lc;
+	unsigned long flags;
 	u64 ctlreg;
 
 	if (set) {
@@ -591,9 +603,11 @@ void smp_ctl_set_clear_bit(int cr, int bit, bool set)
 		parms.andval = ~(1UL << bit);
 	}
 	spin_lock(&ctl_lock);
-	get_abs_lowcore(ctlreg, cregs_save_area[cr]);
+	abs_lc = get_abs_lowcore(&flags);
+	ctlreg = abs_lc->cregs_save_area[cr];
 	ctlreg = (ctlreg & parms.andval) | parms.orval;
-	put_abs_lowcore(cregs_save_area[cr], ctlreg);
+	abs_lc->cregs_save_area[cr] = ctlreg;
+	put_abs_lowcore(abs_lc, flags);
 	spin_unlock(&ctl_lock);
 	on_each_cpu(smp_ctl_bit_callback, &parms, 1);
 }
@@ -1281,6 +1295,8 @@ int __init smp_reinit_ipl_cpu(void)
 	__ctl_clear_bit(0, 28); /* disable lowcore protection */
 	S390_lowcore.mcesad = mcesad;
 	__ctl_load(cr0, 0, 0);
+	if (abs_lowcore_map(0, lc, false))
+		panic("Couldn't remap absolute lowcore");
 	lowcore_ptr[0] = lc;
 	local_mcck_enable();
 	local_irq_restore(flags);
diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
index 4a154a084966..97d66a3e60fb 100644
--- a/arch/s390/mm/init.c
+++ b/arch/s390/mm/init.c
@@ -37,7 +37,7 @@
 #include <asm/kfence.h>
 #include <asm/ptdump.h>
 #include <asm/dma.h>
-#include <asm/lowcore.h>
+#include <asm/abs_lowcore.h>
 #include <asm/tlb.h>
 #include <asm/tlbflush.h>
 #include <asm/sections.h>
diff --git a/arch/s390/mm/maccess.c b/arch/s390/mm/maccess.c
index d6d84e02f35a..b8451ddbb3d6 100644
--- a/arch/s390/mm/maccess.c
+++ b/arch/s390/mm/maccess.c
@@ -15,6 +15,7 @@
 #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)
@@ -148,46 +149,20 @@ int memcpy_real(void *dest, unsigned long src, size_t count)
 }
 
 /*
- * Copy memory in absolute mode (kernel to kernel)
+ * Find CPU that owns swapped prefix page
  */
-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)
+static int get_swapped_owner(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 1;
+		return cpu;
 	}
-	return 0;
+	return -1;
 }
 
 /*
@@ -200,17 +175,35 @@ 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();
-	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);
+	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_enable();
+out:
+	put_cpu();
 	cpus_read_unlock();
 	return bounce;
 }
diff --git a/arch/s390/mm/vmem.c b/arch/s390/mm/vmem.c
index 1c86de9dd87f..a50a809e024f 100644
--- a/arch/s390/mm/vmem.c
+++ b/arch/s390/mm/vmem.c
@@ -561,6 +561,103 @@ int vmem_add_mapping(unsigned long start, unsigned long size)
 }
 
 /*
+ * Allocate new or return existing page-table entry, but do not map it
+ * to any physical address. If missing, allocate segment- and region-
+ * table entries along. Meeting a large segment- or region-table entry
+ * while traversing is an error, since the function is expected to be
+ * called against virtual regions reserverd for 4KB mappings only.
+ */
+static pte_t *vmem_get_alloc_pte(unsigned long addr, bool alloc)
+{
+	pte_t *ptep = NULL;
+	pgd_t *pgd;
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd;
+	pte_t *pte;
+
+	pgd = pgd_offset_k(addr);
+	if (pgd_none(*pgd)) {
+		if (!alloc)
+			goto out;
+		p4d = vmem_crst_alloc(_REGION2_ENTRY_EMPTY);
+		if (!p4d)
+			goto out;
+		pgd_populate(&init_mm, pgd, p4d);
+	}
+	p4d = p4d_offset(pgd, addr);
+	if (p4d_none(*p4d)) {
+		if (!alloc)
+			goto out;
+		pud = vmem_crst_alloc(_REGION3_ENTRY_EMPTY);
+		if (!pud)
+			goto out;
+		p4d_populate(&init_mm, p4d, pud);
+	}
+	pud = pud_offset(p4d, addr);
+	if (pud_none(*pud)) {
+		if (!alloc)
+			goto out;
+		pmd = vmem_crst_alloc(_SEGMENT_ENTRY_EMPTY);
+		if (!pmd)
+			goto out;
+		pud_populate(&init_mm, pud, pmd);
+	} else if (WARN_ON_ONCE(pud_large(*pud))) {
+		goto out;
+	}
+	pmd = pmd_offset(pud, addr);
+	if (pmd_none(*pmd)) {
+		if (!alloc)
+			goto out;
+		pte = vmem_pte_alloc();
+		if (!pte)
+			goto out;
+		pmd_populate(&init_mm, pmd, pte);
+	} else if (WARN_ON_ONCE(pmd_large(*pmd))) {
+		goto out;
+	}
+	ptep = pte_offset_kernel(pmd, addr);
+out:
+	return ptep;
+}
+
+int __vmem_map_4k_page(unsigned long addr, unsigned long phys, pgprot_t prot, bool alloc)
+{
+	pte_t *ptep, pte;
+
+	if (!IS_ALIGNED(addr, PAGE_SIZE))
+		return -EINVAL;
+	ptep = vmem_get_alloc_pte(addr, alloc);
+	if (!ptep)
+		return -ENOMEM;
+	__ptep_ipte(addr, ptep, 0, 0, IPTE_GLOBAL);
+	pte = mk_pte_phys(phys, prot);
+	set_pte(ptep, pte);
+	return 0;
+}
+
+int vmem_map_4k_page(unsigned long addr, unsigned long phys, pgprot_t prot)
+{
+	int rc;
+
+	mutex_lock(&vmem_mutex);
+	rc = __vmem_map_4k_page(addr, phys, prot, true);
+	mutex_unlock(&vmem_mutex);
+	return rc;
+}
+
+void vmem_unmap_4k_page(unsigned long addr)
+{
+	pte_t *ptep;
+
+	mutex_lock(&vmem_mutex);
+	ptep = virt_to_kpte(addr);
+	__ptep_ipte(addr, ptep, 0, 0, IPTE_GLOBAL);
+	pte_clear(&init_mm, addr, ptep);
+	mutex_unlock(&vmem_mutex);
+}
+
+/*
  * map whole physical memory to virtual memory (identity mapping)
  * we reserve enough space in the vmalloc area for vmemmap to hotplug
  * additional memory segments.