From mboxrd@z Thu Jan 1 00:00:00 1970 From: ard.biesheuvel@linaro.org (Ard Biesheuvel) Date: Sun, 11 Sep 2016 15:38:34 +0100 Subject: [PATCH] arm64: mm: move zero page from .bss to right before swapper_pg_dir Message-ID: <1473604714-5512-1-git-send-email-ard.biesheuvel@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 --- 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