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| author | Ingo Molnar <mingo@kernel.org> | 2015-04-08 09:01:54 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2015-04-08 09:01:54 +0200 |
| commit | 4bcc7827b02feea2c762fa6d46a1bffb300d7403 (patch) | |
| tree | 45fd2b64247cd44201fe519720494d4bf01b7014 /arch/x86/kernel/entry_64.S | |
| parent | 3f705dfdf85a6416f5f12e52b7610144a99cbedc (diff) | |
| parent | f22e6e847115abc3a0e2ad7bb18d243d42275af1 (diff) | |
| download | blackbird-op-linux-4bcc7827b02feea2c762fa6d46a1bffb300d7403.tar.gz blackbird-op-linux-4bcc7827b02feea2c762fa6d46a1bffb300d7403.zip | |
Merge tag 'v4.0-rc7' into x86/asm, to resolve conflicts
Conflicts:
arch/x86/kernel/entry_64.S
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/kernel/entry_64.S')
| -rw-r--r-- | arch/x86/kernel/entry_64.S | 16 |
1 files changed, 15 insertions, 1 deletions
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index f4270ff73f2a..65485b3baa59 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -706,7 +706,21 @@ retint_swapgs: /* return to user-space */ cmpq %r11,EFLAGS(%rsp) /* R11 == RFLAGS */ jne opportunistic_sysret_failed - testq $X86_EFLAGS_RF,%r11 /* sysret can't restore RF */ + /* + * SYSRET can't restore RF. SYSRET can restore TF, but unlike IRET, + * restoring TF results in a trap from userspace immediately after + * SYSRET. This would cause an infinite loop whenever #DB happens + * with register state that satisfies the opportunistic SYSRET + * conditions. For example, single-stepping this user code: + * + * movq $stuck_here,%rcx + * pushfq + * popq %r11 + * stuck_here: + * + * would never get past 'stuck_here'. + */ + testq $(X86_EFLAGS_RF|X86_EFLAGS_TF), %r11 jnz opportunistic_sysret_failed /* nothing to check for RSP */ |
