From: ard.biesheuvel@linaro.org (Ard Biesheuvel)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] arm64: mm: move zero page from .bss to right before swapper_pg_dir
Date: Sun, 11 Sep 2016 15:38:34 +0100 [thread overview]
Message-ID: <1473604714-5512-1-git-send-email-ard.biesheuvel@linaro.org> (raw)
Move the statically allocated zero page from the .bss section to right
before swapper_pg_dir. This allows us to refer to its physical address
by simply reading TTBR1_EL1 (which always points to swapper_pg_dir and
always has its ASID field cleared), and subtracting PAGE_SIZE.
Inspired-by: http://marc.info/?l=linux-arm-kernel&m=147282867511801
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
arch/arm64/include/asm/mmu_context.h | 10 ++++++----
arch/arm64/kernel/head.S | 1 -
arch/arm64/kernel/vmlinux.lds.S | 2 ++
arch/arm64/mm/mmu.c | 1 -
4 files changed, 8 insertions(+), 6 deletions(-)
diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h
index b1892a0dbcb0..94461ba5febd 100644
--- a/arch/arm64/include/asm/mmu_context.h
+++ b/arch/arm64/include/asm/mmu_context.h
@@ -49,13 +49,15 @@ static inline void contextidr_thread_switch(struct task_struct *next)
*/
static inline void cpu_set_reserved_ttbr0(void)
{
- unsigned long ttbr = virt_to_phys(empty_zero_page);
+ unsigned long dummy;
- asm(
+ asm volatile(
+ " mrs %0, ttbr1_el1 // get TTBR1\n"
+ " sub %0, %0, %1 // subtract PAGE_SIZE\n"
" msr ttbr0_el1, %0 // set TTBR0\n"
" isb"
- :
- : "r" (ttbr));
+ : "=&r" (dummy)
+ : "I" (PAGE_SIZE));
}
/*
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 8bc9458f9add..6020b884b076 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -449,7 +449,6 @@ __primary_switched:
adr_l x2, __bss_stop
sub x2, x2, x0
bl __pi_memset
- dsb ishst // Make zero page visible to PTW
#ifdef CONFIG_KASAN
bl kasan_early_init
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 659963d40bb4..a14eb8ff5144 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -193,6 +193,8 @@ SECTIONS
. = ALIGN(PAGE_SIZE);
idmap_pg_dir = .;
. += IDMAP_DIR_SIZE;
+ empty_zero_page = .;
+ . += PAGE_SIZE;
swapper_pg_dir = .;
. += SWAPPER_DIR_SIZE;
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 4989948d1feb..539ce9d11325 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -53,7 +53,6 @@ EXPORT_SYMBOL(kimage_voffset);
* Empty_zero_page is a special page that is used for zero-initialized data
* and COW.
*/
-unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)] __page_aligned_bss;
EXPORT_SYMBOL(empty_zero_page);
static pte_t bm_pte[PTRS_PER_PTE] __page_aligned_bss;
--
2.7.4
next reply other threads:[~2016-09-11 14:38 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-11 14:38 Ard Biesheuvel [this message]
2016-09-11 16:40 ` [PATCH] arm64: mm: move zero page from .bss to right before swapper_pg_dir Ard Biesheuvel
2016-09-12 12:57 ` Mark Rutland
2016-09-12 14:17 ` Ard Biesheuvel
2016-09-12 14:20 ` Catalin Marinas
-- strict thread matches above, loose matches on Subject: below --
2016-09-12 14:16 Ard Biesheuvel
2016-09-12 14:59 ` Mark Rutland
2016-09-12 15:12 ` Ard Biesheuvel
2016-09-12 15:40 ` Mark Rutland
2016-09-12 15:54 ` Ard Biesheuvel
2016-09-12 16:26 ` Mark Rutland
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