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Subject[PATCH 7/9] x86/mm: Make MAX_PHYSADDR_BITS and MAX_PHYSMEM_BITS dynamic
Date
For boot-time switching between paging modes, we need to be able to
adjust size of physical address space at runtime.

As part of making physical address space size variable, we have to make
X86_5LEVEL dependent on SPARSEMEM_VMEMMAP. !SPARSEMEM_VMEMMAP
configuration doesn't build with variable MAX_PHYSMEM_BITS.

For !SPARSEMEM_VMEMMAP SECTIONS_WIDTH depends on MAX_PHYSMEM_BITS:

SECTIONS_WIDTH
SECTIONS_SHIFT
MAX_PHYSMEM_BITS

And SECTIONS_WIDTH is used on pre-processor stage, it doesn't work if it's
dyncamic. See include/linux/page-flags-layout.h.

Affect on kernel image size:

text data bss dec hex filename
8628393 4734340 1368064 14730797 e0c62d vmlinux.before
8628892 4734340 1368064 14731296 e0c820 vmlinux.after

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
arch/x86/Kconfig | 1 +
arch/x86/include/asm/pgtable_64_types.h | 2 +-
arch/x86/include/asm/sparsemem.h | 9 ++-------
arch/x86/kernel/setup.c | 5 ++---
4 files changed, 6 insertions(+), 11 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index f925274ddf79..0d780a3ee924 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1472,6 +1472,7 @@ config X86_PAE
config X86_5LEVEL
bool "Enable 5-level page tables support"
select DYNAMIC_MEMORY_LAYOUT
+ select SPARSEMEM_VMEMMAP
depends on X86_64
---help---
5-level paging enables access to larger address space:
diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
index 0c48d80e11d4..59d971c85de5 100644
--- a/arch/x86/include/asm/pgtable_64_types.h
+++ b/arch/x86/include/asm/pgtable_64_types.h
@@ -95,7 +95,7 @@ extern unsigned int ptrs_per_p4d;
* range must not overlap with anything except the KASAN shadow area, which
* is correct as KASAN disables KASLR.
*/
-#define MAXMEM _AC(__AC(1, UL) << MAX_PHYSMEM_BITS, UL)
+#define MAXMEM (1UL << MAX_PHYSMEM_BITS)

#define LDT_PGD_ENTRY_L4 -3UL
#define LDT_PGD_ENTRY_L5 -112UL
diff --git a/arch/x86/include/asm/sparsemem.h b/arch/x86/include/asm/sparsemem.h
index 4fc1e9d3c43e..4617a2bf123c 100644
--- a/arch/x86/include/asm/sparsemem.h
+++ b/arch/x86/include/asm/sparsemem.h
@@ -27,13 +27,8 @@
# endif
#else /* CONFIG_X86_32 */
# define SECTION_SIZE_BITS 27 /* matt - 128 is convenient right now */
-# ifdef CONFIG_X86_5LEVEL
-# define MAX_PHYSADDR_BITS 52
-# define MAX_PHYSMEM_BITS 52
-# else
-# define MAX_PHYSADDR_BITS 44
-# define MAX_PHYSMEM_BITS 46
-# endif
+# define MAX_PHYSADDR_BITS (pgtable_l5_enabled ? 52 : 44)
+# define MAX_PHYSMEM_BITS (pgtable_l5_enabled ? 52 : 46)
#endif

#endif /* CONFIG_SPARSEMEM */
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 1ae67e982af7..399d0f7fa8f1 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -189,9 +189,7 @@ struct ist_info ist_info;
#endif

#else
-struct cpuinfo_x86 boot_cpu_data __read_mostly = {
- .x86_phys_bits = MAX_PHYSMEM_BITS,
-};
+struct cpuinfo_x86 boot_cpu_data __read_mostly;
EXPORT_SYMBOL(boot_cpu_data);
#endif

@@ -851,6 +849,7 @@ void __init setup_arch(char **cmdline_p)
__flush_tlb_all();
#else
printk(KERN_INFO "Command line: %s\n", boot_command_line);
+ boot_cpu_data.x86_phys_bits = MAX_PHYSMEM_BITS;
#endif

/*
--
2.15.1
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