This is a note to let you know that I've just added the patch titled
x86/speculation: Avoid __switch_to_xtra() calls
to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86speculation_Avoid___switch_to_xtra_calls.patch
and it can be found in the queue-4.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
Subject: x86/speculation: Avoid __switch_to_xtra() calls
From: Thomas Gleixner tglx@xxxxxxxxxxxxx
Date: Sun Nov 25 19:33:48 2018 +0100
From: Thomas Gleixner tglx@xxxxxxxxxxxxx
commit 5635d99953f04b550738f6f4c1c532667c3fd872 upstream
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@xxxxxxxxxxxxx>
Reviewed-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Jiri Kosina <jkosina@xxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: David Woodhouse <dwmw@xxxxxxxxxxxx>
Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Casey Schaufler <casey.schaufler@xxxxxxxxx>
Cc: Asit Mallick <asit.k.mallick@xxxxxxxxx>
Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
Cc: Jon Masters <jcm@xxxxxxxxxx>
Cc: Waiman Long <longman9394@xxxxxxxxx>
Cc: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Dave Stewart <david.c.stewart@xxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20181125185005.374062201@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/include/asm/thread_info.h | 13 +++++++++++--
arch/x86/kernel/process.h | 15 +++++++++++++++
2 files changed, 26 insertions(+), 2 deletions(-)
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -149,9 +149,18 @@ 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)
--- 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(struc
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.
Patches currently in stable-queue which might be from tglx@xxxxxxxxxxxxx are
queue-4.14/x86speculation_Prepare_for_conditional_IBPB_in_switch_mm.patch
queue-4.14/x86speculation_Rework_SMT_state_change.patch
queue-4.14/x86bugs_Switch_the_selection_of_mitigation_from_CPU_vendor_to_CPU_features.patch
queue-4.14/x86Kconfig_Select_SCHED_SMT_if_SMP_enabled.patch
queue-4.14/x86speculation_Move_STIPBIBPB_string_conditionals_out_of_cpu_show_common().patch
queue-4.14/x86speculation_Propagate_information_about_RSB_filling_mitigation_to_sysfs.patch
queue-4.14/x86speculation_Prepare_arch_smt_update_for_PRCTL_mode.patch
queue-4.14/x86speculation_Enable_cross-hyperthread_spectre_v2_STIBP_mitigation.patch
queue-4.14/bpf-prevent-memory-disambiguation-attack.patch
queue-4.14/x86speculation_Prevent_stale_SPEC_CTRL_msr_content.patch
queue-4.14/ptrace_Remove_unused_ptrace_may_access_sched_and_MODE_IBRS.patch
queue-4.14/x86speculation_Mark_string_arrays_const_correctly.patch
queue-4.14/x86process_Consolidate_and_simplify_switch_to_xtra_code.patch
queue-4.14/x86speculation_Apply_IBPB_more_strictly_to_avoid_cross-process_data_leak.patch
queue-4.14/x86speculation_Enable_prctl_mode_for_spectre_v2_user.patch
queue-4.14/x86speculation_Rename_SSBD_update_functions.patch
queue-4.14/x86speculation_Add_command_line_control_for_indirect_branch_speculation.patch
queue-4.14/x86l1tf_Show_actual_SMT_state.patch
queue-4.14/x86speculation_Split_out_TIF_update.patch
queue-4.14/schedsmt_Make_sched_smt_present_track_topology.patch
queue-4.14/x86retpoline_Make_CONFIG_RETPOLINE_depend_on_compiler_support.patch
queue-4.14/schedsmt_Expose_sched_smt_present_static_key.patch
queue-4.14/x86speculation_Reorder_the_spec_v2_code.patch
queue-4.14/x86speculation_Add_prctl()_control_for_indirect_branch_speculation.patch
queue-4.14/x86bugs_Update_when_to_check_for_the_LS_CFG_SSBD_mitigation.patch
queue-4.14/x86speculation_Provide_IBPB_always_command_line_options.patch
queue-4.14/x86speculation_Prepare_for_per_task_indirect_branch_speculation_control.patch
queue-4.14/x86speculataion_Mark_command_line_parser_data___initdata.patch
queue-4.14/x86speculation_Disable_STIBP_when_enhanced_IBRS_is_in_use.patch
queue-4.14/x86speculation_Reorganize_speculation_control_MSRs_update.patch
queue-4.14/x86bugs_Add_AMDs_SPEC_CTRL_MSR_usage.patch
queue-4.14/x86speculation_Clean_up_spectre_v2_parse_cmdline().patch
queue-4.14/x86speculation_Update_the_TIF_SSBD_comment.patch
queue-4.14/x86speculation_Add_seccomp_Spectre_v2_user_space_protection_mode.patch
queue-4.14/x86bugs_Add_AMDs_variant_of_SSB_NO.patch
queue-4.14/schedcore_Fix_cpu.max_vs._cpuhotplug_deadlock.patch
queue-4.14/x86speculation_Unify_conditional_spectre_v2_print_functions.patch
queue-4.14/x86speculation_Avoid___switch_to_xtra_calls.patch
queue-4.14/x86speculation_Remove_unnecessary_ret_variable_in_cpu_show_common().patch
queue-4.14/x86bugs_Fix_the_AMD_SSBD_usage_of_the_SPEC_CTRL_MSR.patch
queue-4.14/x86retpoline_Remove_minimal_retpoline_support.patch
queue-4.14/x86speculation_Add_RETPOLINE_AMD_support_to_the_inline_asm_CALL_NOSPEC_variant.patch
