linux-kernel - [PATCH 08/18] arm64: mm: Add arm64_kernel_mapped_at

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Date:   Fri, 17 Nov 2017 18:21:51 +0000
From:   Will Deacon <will.deacon@....com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, catalin.marinas@....com,
        mark.rutland@....com, ard.biesheuvel@...aro.org,
        sboyd@...eaurora.org, dave.hansen@...ux.intel.com,
        keescook@...omium.org, Will Deacon <will.deacon@....com>
Subject: [PATCH 08/18] arm64: mm: Add arm64_kernel_mapped_at_el0 helper using static key

In order for code such as TLB invalidation to operate efficiently when
the decision to map the kernel at EL0 is determined at runtime, this
patch introduces a helper function, arm64_kernel_mapped_at_el0, which
uses a static key that will later be hooked up to a command-line option.

Signed-off-by: Will Deacon <will.deacon@....com>
---
 arch/arm64/include/asm/mmu.h | 11 +++++++++++
 arch/arm64/mm/mmu.c          |  5 +++++
 2 files changed, 16 insertions(+)

diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
index 01bfb184f2a8..a84f851409ca 100644
--- a/arch/arm64/include/asm/mmu.h
+++ b/arch/arm64/include/asm/mmu.h
@@ -19,6 +19,8 @@
 #define MMCF_AARCH32	0x1	/* mm context flag for AArch32 executables */
 #define USER_ASID_FLAG	(UL(1) << 48)
 
+#ifndef __ASSEMBLY__
+
 typedef struct {
 	atomic64_t	id;
 	void		*vdso;
@@ -32,6 +34,14 @@ typedef struct {
  */
 #define ASID(mm)	((mm)->context.id.counter & 0xffff)
 
+DECLARE_STATIC_KEY_TRUE(__unmap_kernel_at_el0);
+
+static inline bool arm64_kernel_mapped_at_el0(void)
+{
+	return !IS_ENABLED(CONFIG_UNMAP_KERNEL_AT_EL0) ||
+	       !static_branch_likely(&__unmap_kernel_at_el0);
+}
+
 extern void paging_init(void);
 extern void bootmem_init(void);
 extern void __iomem *early_io_map(phys_addr_t phys, unsigned long virt);
@@ -42,4 +52,5 @@ extern void create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
 extern void *fixmap_remap_fdt(phys_addr_t dt_phys);
 extern void mark_linear_text_alias_ro(void);
 
+#endif	/* !__ASSEMBLY__ */
 #endif
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index f1eb15e0e864..a75858267b6d 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -525,6 +525,11 @@ static int __init parse_rodata(char *arg)
 }
 early_param("rodata", parse_rodata);
 
+#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
+DEFINE_STATIC_KEY_TRUE(__unmap_kernel_at_el0);
+EXPORT_SYMBOL_GPL(__unmap_kernel_at_el0);
+#endif
+
 /*
  * Create fine-grained mappings for the kernel.
  */
-- 
2.1.4