s390/mm: start kernel with DAT enabled

The setup of the kernel virtual address space is spread
throughout the sources, boot stages and config options
like this:

1. The available physical memory regions are queried
   and stored as mem_detect information for later use
   in the decompressor.

2. Based on the physical memory availability the virtual
   memory layout is established in the decompressor;

3. If CONFIG_KASAN is disabled the kernel paging setup
   code populates kernel pgtables and turns DAT mode on.
   It uses the information stored at step [1].

4. If CONFIG_KASAN is enabled the kernel early boot
   kasan setup populates kernel pgtables and turns DAT
   mode on. It uses the information stored at step [1].

   The kasan setup creates early_pg_dir directory and
   directly overwrites swapper_pg_dir entries to make
   shadow memory pages available.

Move the kernel virtual memory setup to the decompressor
and start the kernel with DAT turned on right from the
very first istruction. That completely eliminates the
boot phase when the kernel runs in DAT-off mode, simplies
the overall design and consolidates pgtables setup.

The identity mapping is created in the decompressor, while
kasan shadow mappings are still created by the early boot
kernel code.

Share with decompressor the existing kasan memory allocator.
It decreases the size of a newly requested memory block from
pgalloc_pos and ensures that kernel image is not overwritten.
pgalloc_low and pgalloc_pos pointers are made preserved boot
variables for that.

Use the bootdata infrastructure to setup swapper_pg_dir
and invalid_pg_dir directories used by the kernel later.
The interim early_pg_dir directory established by the
kasan initialization code gets eliminated as result.

As the kernel runs in DAT-on mode only the PSW_KERNEL_BITS
define gets PSW_MASK_DAT bit by default. Additionally, the
setup_lowcore_dat_off() and setup_lowcore_dat_on() routines
get merged, since there is no DAT-off mode stage anymore.

The memory mappings are created with RW+X protection that
allows the early boot code setting up all necessary data
and services for the kernel being booted. Just before the
paging is enabled the memory protection is changed to
RO+X for text, RO+NX for read-only data and RW+NX for
kernel data and the identity mapping.

Reviewed-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>

4 files changed, 5 insertions, 5 deletions

diff --git a/arch/s390/include/asm/kasan.h b/arch/s390/include/asm/kasan.h
index 2768d5db181f..f7244cc16240 100644
--- a/arch/s390/include/asm/kasan.h
+++ b/arch/s390/include/asm/kasan.h
@@ -14,8 +14,6 @@
 #define KASAN_SHADOW_END	(KASAN_SHADOW_START + KASAN_SHADOW_SIZE)
 
 extern void kasan_early_init(void);
-extern void kasan_copy_shadow_mapping(void);
-extern void kasan_free_early_identity(void);
 
 /*
  * Estimate kasan memory requirements, which it will reserve
@@ -43,8 +41,6 @@ static inline unsigned long kasan_estimate_memory_needs(unsigned long physmem)
 }
 #else
 static inline void kasan_early_init(void) { }
-static inline void kasan_copy_shadow_mapping(void) { }
-static inline void kasan_free_early_identity(void) { }
 static inline unsigned long kasan_estimate_memory_needs(unsigned long physmem) { return 0; }
 #endif
 
diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 0170f95f3b91..0f1eba005f6d 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -23,6 +23,7 @@
 #include <asm/uv.h>
 
 extern pgd_t swapper_pg_dir[];
+extern pgd_t invalid_pg_dir[];
 extern void paging_init(void);
 extern unsigned long s390_invalid_asce;
 
diff --git a/arch/s390/include/asm/ptrace.h b/arch/s390/include/asm/ptrace.h
index 8bae33ab320a..bfb8c3cb8aee 100644
--- a/arch/s390/include/asm/ptrace.h
+++ b/arch/s390/include/asm/ptrace.h
@@ -26,7 +26,7 @@
 #ifndef __ASSEMBLY__
 
 #define PSW_KERNEL_BITS	(PSW_DEFAULT_KEY | PSW_MASK_BASE | PSW_ASC_HOME | \
-			 PSW_MASK_EA | PSW_MASK_BA)
+			 PSW_MASK_EA | PSW_MASK_BA | PSW_MASK_DAT)
 #define PSW_USER_BITS	(PSW_MASK_DAT | PSW_MASK_IO | PSW_MASK_EXT | \
 			 PSW_DEFAULT_KEY | PSW_MASK_BASE | PSW_MASK_MCHECK | \
 			 PSW_MASK_PSTATE | PSW_ASC_PRIMARY)
diff --git a/arch/s390/include/asm/setup.h b/arch/s390/include/asm/setup.h
index 77e6506898f5..6792ce28d37a 100644
--- a/arch/s390/include/asm/setup.h
+++ b/arch/s390/include/asm/setup.h
@@ -73,6 +73,9 @@ extern unsigned int zlib_dfltcc_support;
 
 extern int noexec_disabled;
 extern unsigned long ident_map_size;
+extern unsigned long pgalloc_pos;
+extern unsigned long pgalloc_end;
+extern unsigned long pgalloc_low;
 
 /* The Write Back bit position in the physaddr is given by the SLPC PCI */
 extern unsigned long mio_wb_bit_mask;