[PATCH 1/3] powerpc: Define empty_zero_page[] in C

Don't duplicate swapper_pg_dir[] in each platform's head.S

Define it in mm/pgtable.c

Define MAX_PTRS_PER_PGD because on book3s/64 PTRS_PER_PGD is
not a constant.

Signed-off-by: Christophe Leroy <redacted>
---
 arch/powerpc/include/asm/book3s/64/pgtable.h |  3 +++
 arch/powerpc/include/asm/pgtable.h           |  4 ++++
 arch/powerpc/kernel/asm-offsets.c            |  5 -----
 arch/powerpc/kernel/head_40x.S               | 11 -----------
 arch/powerpc/kernel/head_44x.S               | 17 +----------------
 arch/powerpc/kernel/head_64.S                | 15 ---------------
 arch/powerpc/kernel/head_8xx.S               | 12 ------------
 arch/powerpc/kernel/head_book3s_32.S         | 11 -----------
 arch/powerpc/kernel/head_fsl_booke.S         | 12 ------------
 arch/powerpc/mm/pgtable.c                    |  2 ++
 10 files changed, 10 insertions(+), 82 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
index a666d561b44d..4d9941b2fe51 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h

@@ -232,6 +232,9 @@ extern unsigned long __pmd_frag_size_shift;
 #define PTRS_PER_PUD	(1 << PUD_INDEX_SIZE)
 #define PTRS_PER_PGD	(1 << PGD_INDEX_SIZE)
 
+#define MAX_PTRS_PER_PGD	(1 << (H_PGD_INDEX_SIZE > RADIX_PGD_INDEX_SIZE ? \
+				       H_PGD_INDEX_SIZE : RADIX_PGD_INDEX_SIZE))
+
 /* PMD_SHIFT determines what a second-level page table entry can map */
 #define PMD_SHIFT	(PAGE_SHIFT + PTE_INDEX_SIZE)
 #define PMD_SIZE	(1UL << PMD_SHIFT)

diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
index c6a676714f04..b9c8641654f4 100644
--- a/arch/powerpc/include/asm/pgtable.h
+++ b/arch/powerpc/include/asm/pgtable.h

@@ -41,6 +41,10 @@ struct mm_struct;
 
 #ifndef __ASSEMBLY__
 
+#ifndef MAX_PTRS_PER_PGD
+#define MAX_PTRS_PER_PGD PTRS_PER_PGD
+#endif
+
 /* Keep these as a macros to avoid include dependency mess */
 #define pte_page(x)		pfn_to_page(pte_pfn(x))
 #define mk_pte(page, pgprot)	pfn_pte(page_to_pfn(page), (pgprot))

diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index 0480f4006e0c..f1b6ff14c8a0 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c

@@ -361,11 +361,6 @@ int main(void)
 	DEFINE(BUG_ENTRY_SIZE, sizeof(struct bug_entry));
 #endif
 
-#ifdef CONFIG_PPC_BOOK3S_64
-	DEFINE(PGD_TABLE_SIZE, (sizeof(pgd_t) << max(RADIX_PGD_INDEX_SIZE, H_PGD_INDEX_SIZE)));
-#else
-	DEFINE(PGD_TABLE_SIZE, PGD_TABLE_SIZE);
-#endif
 	DEFINE(PTE_SIZE, sizeof(pte_t));
 
 #ifdef CONFIG_KVM

diff --git a/arch/powerpc/kernel/head_40x.S b/arch/powerpc/kernel/head_40x.S
index 92b6c7356161..7d72ee5ab387 100644
--- a/arch/powerpc/kernel/head_40x.S
+++ b/arch/powerpc/kernel/head_40x.S

@@ -701,14 +701,3 @@ _GLOBAL(abort)
         mfspr   r13,SPRN_DBCR0
         oris    r13,r13,DBCR0_RST_SYSTEM@h
         mtspr   SPRN_DBCR0,r13
-
-/* We put a few things here that have to be page-aligned. This stuff
- * goes at the beginning of the data segment, which is page-aligned.
- */
-	.data
-	.align	12
-	.globl	sdata
-sdata:
-	.globl	swapper_pg_dir
-swapper_pg_dir:
-	.space	PGD_TABLE_SIZE

diff --git a/arch/powerpc/kernel/head_44x.S b/arch/powerpc/kernel/head_44x.S
index e037eb615757..ddc978a2d381 100644
--- a/arch/powerpc/kernel/head_44x.S
+++ b/arch/powerpc/kernel/head_44x.S

@@ -1233,23 +1233,8 @@ head_start_common:
 	isync
 	blr
 
-/*
- * We put a few things here that have to be page-aligned. This stuff
- * goes at the beginning of the data segment, which is page-aligned.
- */
-	.data
-	.align	PAGE_SHIFT
-	.globl	sdata
-sdata:
-
-/*
- * To support >32-bit physical addresses, we use an 8KB pgdir.
- */
-	.globl	swapper_pg_dir
-swapper_pg_dir:
-	.space	PGD_TABLE_SIZE
-
 #ifdef CONFIG_SMP
+	.data
 	.align	12
 temp_boot_stack:
 	.space	1024

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index 730838c7ca39..79f2d1e61abd 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S

@@ -997,18 +997,3 @@ start_here_common:
 0:	trap
 	EMIT_BUG_ENTRY 0b, __FILE__, __LINE__, 0
 	.previous
-
-/*
- * We put a few things here that have to be page-aligned.
- * This stuff goes at the beginning of the bss, which is page-aligned.
- */
-	.section ".bss"
-/*
- * pgd dir should be aligned to PGD_TABLE_SIZE which is 64K.
- * We will need to find a better way to fix this
- */
-	.align	16
-
-	.globl	swapper_pg_dir
-swapper_pg_dir:
-	.space	PGD_TABLE_SIZE

diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
index 5ce42dfac061..9bdb95f5694f 100644
--- a/arch/powerpc/kernel/head_8xx.S
+++ b/arch/powerpc/kernel/head_8xx.S

@@ -786,15 +786,3 @@ _GLOBAL(mmu_pin_tlb)
 	mtspr	SPRN_SRR1, r10
 	mtspr	SPRN_SRR0, r11
 	rfi
-
-/*
- * We put a few things here that have to be page-aligned.
- * This stuff goes at the beginning of the data segment,
- * which is page-aligned.
- */
-	.data
-	.globl	sdata
-sdata:
-	.globl	swapper_pg_dir
-swapper_pg_dir:
-	.space	PGD_TABLE_SIZE

diff --git a/arch/powerpc/kernel/head_book3s_32.S b/arch/powerpc/kernel/head_book3s_32.S
index 79c744afc6b6..689c9d37f193 100644
--- a/arch/powerpc/kernel/head_book3s_32.S
+++ b/arch/powerpc/kernel/head_book3s_32.S

@@ -1266,18 +1266,7 @@ setup_usbgecko_bat:
 	blr
 #endif
 
-/*
- * We put a few things here that have to be page-aligned.
- * This stuff goes at the beginning of the data segment,
- * which is page-aligned.
- */
 	.data
-	.globl	sdata
-sdata:
-	.globl	swapper_pg_dir
-swapper_pg_dir:
-	.space	PGD_TABLE_SIZE
-
 /* Room for two PTE pointers, usually the kernel and current user pointers
  * to their respective root page table.
  */

diff --git a/arch/powerpc/kernel/head_fsl_booke.S b/arch/powerpc/kernel/head_fsl_booke.S
index f33bc5a8e73e..0f9642f36b49 100644
--- a/arch/powerpc/kernel/head_fsl_booke.S
+++ b/arch/powerpc/kernel/head_fsl_booke.S

@@ -1212,15 +1212,3 @@ _GLOBAL(restore_to_as0)
 	*/
 3:	mr	r3,r5
 	bl	_start
-
-/*
- * We put a few things here that have to be page-aligned. This stuff
- * goes at the beginning of the data segment, which is page-aligned.
- */
-	.data
-	.align	12
-	.globl	sdata
-sdata:
-	.globl	swapper_pg_dir
-swapper_pg_dir:
-	.space	PGD_TABLE_SIZE

diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
index 354611940118..1707ab580ee2 100644
--- a/arch/powerpc/mm/pgtable.c
+++ b/arch/powerpc/mm/pgtable.c

@@ -28,6 +28,8 @@
 #include <asm/hugetlb.h>
 #include <asm/pte-walk.h>
 
+pgd_t swapper_pg_dir[MAX_PTRS_PER_PGD] __page_aligned_bss;
+
 static inline int is_exec_fault(void)
 {
 	return current->thread.regs && TRAP(current->thread.regs) == 0x400;

-- 
2.25.0

Daniel Axtens [off-list ref] writes:

quoted

Hi Christophe,

This breaks booting a radix KVM guest with 4k pages for me:

make pseries_le_defconfig
scripts/config -d CONFIG_PPC_64K_PAGES
scripts/config -e CONFIG_PPC_4K_PAGES
make vmlinux
sudo qemu-system-ppc64 -enable-kvm -M pseries -m 1G -nographic -vga none -smp 4 -cpu host -kernel vmlinux

Boot hangs after printing 'Booting Linux via __start()' and qemu's 'info
registers' reports that it's stuck at the instruction fetch exception.

My host is Power9, 64k page size radix, and
gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0, GNU ld (GNU Binutils for Ubuntu) 2.34

...

quoted

quoted

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index 730838c7ca39..79f2d1e61abd 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S

@@ -997,18 +997,3 @@ start_here_common:
 0:	trap
 	EMIT_BUG_ENTRY 0b, __FILE__, __LINE__, 0
 	.previous
-
-/*
- * We put a few things here that have to be page-aligned.
- * This stuff goes at the beginning of the bss, which is page-aligned.
- */
-	.section ".bss"
-/*
- * pgd dir should be aligned to PGD_TABLE_SIZE which is 64K.
- * We will need to find a better way to fix this
- */
-	.align	16
-
-	.globl	swapper_pg_dir
-swapper_pg_dir:
-	.space	PGD_TABLE_SIZE

This is now 4K aligned whereas it used to be 64K.

This fixes it and is not completely ugly?

diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
index 1707ab580ee2..298469beaa90 100644
--- a/arch/powerpc/mm/pgtable.c
+++ b/arch/powerpc/mm/pgtable.c

@@ -28,7 +28,13 @@
 #include <asm/hugetlb.h>
 #include <asm/pte-walk.h>
 
-pgd_t swapper_pg_dir[MAX_PTRS_PER_PGD] __page_aligned_bss;
+#ifdef CONFIG_PPC64
+#define PGD_ALIGN 0x10000
+#else
+#define PGD_ALIGN PAGE_SIZE
+#endif
+
+pgd_t swapper_pg_dir[MAX_PTRS_PER_PGD] __section(".bss..page_aligned") __aligned(PGD_ALIGN);