diff options
author | Thomas Gleixner <tglx@linutronix.de> | 2018-11-25 19:33:48 +0100 |
---|---|---|
committer | Thomas Gleixner <tglx@linutronix.de> | 2018-11-28 11:57:11 +0100 |
commit | 5635d99953f04b550738f6f4c1c532667c3fd872 (patch) | |
tree | 480aca8dd70c8000890988547e1a3656f329343a | |
parent | ff16701a29cba3aafa0bd1656d766813b2d0a811 (diff) | |
download | linux-5635d99953f04b550738f6f4c1c532667c3fd872.tar.bz2 |
x86/speculation: Avoid __switch_to_xtra() calls
The TIF_SPEC_IB bit does not need to be evaluated in the decision to invoke
__switch_to_xtra() when:
- CONFIG_SMP is disabled
- The conditional STIPB mode is disabled
The TIF_SPEC_IB bit still controls IBPB in both cases so the TIF work mask
checks might invoke __switch_to_xtra() for nothing if TIF_SPEC_IB is the
only set bit in the work masks.
Optimize it out by masking the bit at compile time for CONFIG_SMP=n and at
run time when the static key controlling the conditional STIBP mode is
disabled.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Casey Schaufler <casey.schaufler@intel.com>
Cc: Asit Mallick <asit.k.mallick@intel.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Jon Masters <jcm@redhat.com>
Cc: Waiman Long <longman9394@gmail.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Dave Stewart <david.c.stewart@intel.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20181125185005.374062201@linutronix.de
-rw-r--r-- | arch/x86/include/asm/thread_info.h | 13 | ||||
-rw-r--r-- | arch/x86/kernel/process.h | 15 |
2 files changed, 26 insertions, 2 deletions
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h index fa583ec99e3e..6d201699c651 100644 --- a/arch/x86/include/asm/thread_info.h +++ b/arch/x86/include/asm/thread_info.h @@ -147,9 +147,18 @@ struct thread_info { _TIF_FSCHECK) /* flags to check in __switch_to() */ -#define _TIF_WORK_CTXSW \ +#define _TIF_WORK_CTXSW_BASE \ (_TIF_IO_BITMAP|_TIF_NOCPUID|_TIF_NOTSC|_TIF_BLOCKSTEP| \ - _TIF_SSBD|_TIF_SPEC_IB) + _TIF_SSBD) + +/* + * Avoid calls to __switch_to_xtra() on UP as STIBP is not evaluated. + */ +#ifdef CONFIG_SMP +# define _TIF_WORK_CTXSW (_TIF_WORK_CTXSW_BASE | _TIF_SPEC_IB) +#else +# define _TIF_WORK_CTXSW (_TIF_WORK_CTXSW_BASE) +#endif #define _TIF_WORK_CTXSW_PREV (_TIF_WORK_CTXSW|_TIF_USER_RETURN_NOTIFY) #define _TIF_WORK_CTXSW_NEXT (_TIF_WORK_CTXSW) diff --git a/arch/x86/kernel/process.h b/arch/x86/kernel/process.h index 020fbfac3a27..898e97cf6629 100644 --- a/arch/x86/kernel/process.h +++ b/arch/x86/kernel/process.h @@ -2,6 +2,8 @@ // // Code shared between 32 and 64 bit +#include <asm/spec-ctrl.h> + void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p); /* @@ -14,6 +16,19 @@ static inline void switch_to_extra(struct task_struct *prev, unsigned long next_tif = task_thread_info(next)->flags; unsigned long prev_tif = task_thread_info(prev)->flags; + if (IS_ENABLED(CONFIG_SMP)) { + /* + * Avoid __switch_to_xtra() invocation when conditional + * STIPB is disabled and the only different bit is + * TIF_SPEC_IB. For CONFIG_SMP=n TIF_SPEC_IB is not + * in the TIF_WORK_CTXSW masks. + */ + if (!static_branch_likely(&switch_to_cond_stibp)) { + prev_tif &= ~_TIF_SPEC_IB; + next_tif &= ~_TIF_SPEC_IB; + } + } + /* * __switch_to_xtra() handles debug registers, i/o bitmaps, * speculation mitigations etc. |