linux-kernel - [PATCH 1/3] powerpc: Define empty_zero

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Message-Id: <5838caffa269e0957c5a50cc85477876220298b0.1623063174.git.christophe.leroy@csgroup.eu>
Date:   Mon,  7 Jun 2021 10:56:04 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH 1/3] powerpc: Define empty_zero_page[] in C

At the time being, empty_zero_page[] is defined in each
platform head.S.

Define it in mm/mem.c instead, and put it in BSS section instead
of the DATA section. Commit 5227cfa71f9e ("arm64: mm: place
empty_zero_page in bss") explains why it is interesting to have
it in BSS.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
Applies on top of powerpc next-test with the Fixup for v3 "powerpc/nohash: Refactor update of BDI2000 pointers in switch_mmu_context()".
The last patch of this small series can be applied independently at the cost of a trivial conflict in asm-offsets.c

 arch/powerpc/kernel/head_40x.S       | 4 ----
 arch/powerpc/kernel/head_44x.S       | 4 ----
 arch/powerpc/kernel/head_64.S        | 5 -----
 arch/powerpc/kernel/head_8xx.S       | 6 ------
 arch/powerpc/kernel/head_book3s_32.S | 5 -----
 arch/powerpc/kernel/head_fsl_booke.S | 4 ----
 arch/powerpc/mm/mem.c                | 3 +++
 7 files changed, 3 insertions(+), 28 deletions(-)

diff --git a/arch/powerpc/kernel/head_40x.S b/arch/powerpc/kernel/head_40x.S
index 2717aa860cae..92b6c7356161 100644
--- a/arch/powerpc/kernel/head_40x.S
+++ b/arch/powerpc/kernel/head_40x.S
@@ -709,10 +709,6 @@ _GLOBAL(abort)
 	.align	12
 	.globl	sdata
 sdata:
-	.globl	empty_zero_page
-empty_zero_page:
-	.space	4096
-EXPORT_SYMBOL(empty_zero_page)
 	.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 2c4ffec027a2..e037eb615757 100644
--- a/arch/powerpc/kernel/head_44x.S
+++ b/arch/powerpc/kernel/head_44x.S
@@ -1241,10 +1241,6 @@ head_start_common:
 	.align	PAGE_SHIFT
 	.globl	sdata
 sdata:
-	.globl	empty_zero_page
-empty_zero_page:
-	.space	PAGE_SIZE
-EXPORT_SYMBOL(empty_zero_page)
 
 /*
  * To support >32-bit physical addresses, we use an 8KB pgdir.
diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index ece7f97bafff..730838c7ca39 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -1012,8 +1012,3 @@ start_here_common:
 	.globl	swapper_pg_dir
 swapper_pg_dir:
 	.space	PGD_TABLE_SIZE
-
-	.globl	empty_zero_page
-empty_zero_page:
-	.space	PAGE_SIZE
-EXPORT_SYMBOL(empty_zero_page)
diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
index 817df9fe7fb3..5ce42dfac061 100644
--- a/arch/powerpc/kernel/head_8xx.S
+++ b/arch/powerpc/kernel/head_8xx.S
@@ -795,12 +795,6 @@ _GLOBAL(mmu_pin_tlb)
 	.data
 	.globl	sdata
 sdata:
-	.globl	empty_zero_page
-	.align	PAGE_SHIFT
-empty_zero_page:
-	.space	PAGE_SIZE
-EXPORT_SYMBOL(empty_zero_page)
-
 	.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 326262030279..79c744afc6b6 100644
--- a/arch/powerpc/kernel/head_book3s_32.S
+++ b/arch/powerpc/kernel/head_book3s_32.S
@@ -1274,11 +1274,6 @@ setup_usbgecko_bat:
 	.data
 	.globl	sdata
 sdata:
-	.globl	empty_zero_page
-empty_zero_page:
-	.space	4096
-EXPORT_SYMBOL(empty_zero_page)
-
 	.globl	swapper_pg_dir
 swapper_pg_dir:
 	.space	PGD_TABLE_SIZE
diff --git a/arch/powerpc/kernel/head_fsl_booke.S b/arch/powerpc/kernel/head_fsl_booke.S
index ab718fd5e2a2..f33bc5a8e73e 100644
--- a/arch/powerpc/kernel/head_fsl_booke.S
+++ b/arch/powerpc/kernel/head_fsl_booke.S
@@ -1221,10 +1221,6 @@ _GLOBAL(restore_to_as0)
 	.align	12
 	.globl	sdata
 sdata:
-	.globl	empty_zero_page
-empty_zero_page:
-	.space	4096
-EXPORT_SYMBOL(empty_zero_page)
 	.globl	swapper_pg_dir
 swapper_pg_dir:
 	.space	PGD_TABLE_SIZE
diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 043bbeaf407c..b06e5d969051 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -27,6 +27,9 @@
 unsigned long long memory_limit;
 bool init_mem_is_free;
 
+unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)] __page_aligned_bss;
+EXPORT_SYMBOL(empty_zero_page);
+
 pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
 			      unsigned long size, pgprot_t vma_prot)
 {
-- 
2.25.0