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Subject[PATCH 1/2] arm64: introduce separated bits for mm_context_t flags
Date
Currently mm->context.flags field uses thread_info flags which is not
the best idea for many reasons. For example, mm_context_t doesn't need
most of thread_info flags. And it would be difficult to add new mm-related
flag if needed because it may easily interfere with TIF ones.

To deal with it, the new MMCF_AARCH32 flag is introduced for
mm_context_t->flags, where MMCF prefix stands for mm_context_t flags.
Also, mm_context_t flag doesn't require atomicity and ordering of the
access, so using set/clear_bit() is replaced with simple masks.

RFC: https://lkml.org/lkml/2017/7/31/454
v1:
- changed the MMCF_AARCH32 bit number from 0x1 to 0x0 and added comment
v2:
- using set/clear_bit() is replaced with simple masks.

Signed-off-by: Yury Norov <ynorov@caviumnetworks.com>
---
arch/arm64/include/asm/elf.h | 4 ++--
arch/arm64/include/asm/mmu.h | 2 ++
arch/arm64/kernel/probes/uprobes.c | 2 +-
3 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
index 3288c2b36731..517b9ff0456c 100644
--- a/arch/arm64/include/asm/elf.h
+++ b/arch/arm64/include/asm/elf.h
@@ -139,7 +139,7 @@ typedef struct user_fpsimd_state elf_fpregset_t;

#define SET_PERSONALITY(ex) \
({ \
- clear_bit(TIF_32BIT, &current->mm->context.flags); \
+ current->mm->context.flags = 0; \
clear_thread_flag(TIF_32BIT); \
current->personality &= ~READ_IMPLIES_EXEC; \
})
@@ -195,7 +195,7 @@ typedef compat_elf_greg_t compat_elf_gregset_t[COMPAT_ELF_NGREG];
*/
#define COMPAT_SET_PERSONALITY(ex) \
({ \
- set_bit(TIF_32BIT, &current->mm->context.flags); \
+ current->mm->context.flags = MMCF_AARCH32; \
set_thread_flag(TIF_32BIT); \
})
#define COMPAT_ARCH_DLINFO
diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
index 5468c834b072..e4c474c6501e 100644
--- a/arch/arm64/include/asm/mmu.h
+++ b/arch/arm64/include/asm/mmu.h
@@ -16,6 +16,8 @@
#ifndef __ASM_MMU_H
#define __ASM_MMU_H

+#define MMCF_AARCH32 0x1 /* MM hosts AArch32 executables */
+
typedef struct {
atomic64_t id;
void *vdso;
diff --git a/arch/arm64/kernel/probes/uprobes.c b/arch/arm64/kernel/probes/uprobes.c
index 26c998534dca..636ca0119c0e 100644
--- a/arch/arm64/kernel/probes/uprobes.c
+++ b/arch/arm64/kernel/probes/uprobes.c
@@ -40,7 +40,7 @@ int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm,
probe_opcode_t insn;

/* TODO: Currently we do not support AARCH32 instruction probing */
- if (test_bit(TIF_32BIT, &mm->context.flags))
+ if (mm->context.flags & MMCF_AARCH32)
return -ENOTSUPP;
else if (!IS_ALIGNED(addr, AARCH64_INSN_SIZE))
return -EINVAL;
--
2.11.0
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