Detection of task affinities at API opt-in time is not the best approach, the approach is to kill the task if it runs on a SMT enable core. This is better than not flushing the L1D cache when the task switches from a non-SMT core to an SMT enabled core.
Signed-off-by: Balbir Singh <sbl...@amazon.com> --- To be applied on top of tip commit id b6724f118d44606fddde391ba7527526b3cad211 arch/Kconfig | 4 ++++ arch/x86/Kconfig | 1 + arch/x86/mm/tlb.c | 37 +++++++++++++++++++++---------------- include/linux/sched.h | 10 ++++++++++ 4 files changed, 36 insertions(+), 16 deletions(-) diff --git a/arch/Kconfig b/arch/Kconfig index 546869c3269d..2024486d28a2 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -311,6 +311,10 @@ config ARCH_32BIT_OFF_T still support 32-bit off_t. This option is enabled for all such architectures explicitly. +config ARCH_HAS_PARANOID_L1D_FLUSH + bool + default n + config HAVE_ASM_MODVERSIONS bool help diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 36357c806e8a..02ff6ff71002 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -103,6 +103,7 @@ config X86 select ARCH_WANTS_DYNAMIC_TASK_STRUCT select ARCH_WANT_HUGE_PMD_SHARE select ARCH_WANTS_THP_SWAP if X86_64 + select ARCH_HAS_PARANOID_L1D_FLUSH select BUILDTIME_TABLE_SORT select CLKEVT_I8253 select CLOCKSOURCE_VALIDATE_LAST_CYCLE diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index 88e9ad5142e4..bdc399b86bc7 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -315,31 +315,18 @@ EXPORT_SYMBOL_GPL(leave_mm); int enable_l1d_flush_for_task(struct task_struct *tsk) { - int cpu, ret = 0, i; - /* * Do not enable L1D_FLUSH_OUT if * b. The CPU is not affected by the L1TF bug * c. The CPU does not have L1D FLUSH feature support - * c. The task's affinity is on cores with SMT on. */ if (!boot_cpu_has_bug(X86_BUG_L1TF) || - !static_cpu_has(X86_FEATURE_FLUSH_L1D)) + !boot_cpu_has(X86_FEATURE_FLUSH_L1D)) return -EINVAL; - cpu = get_cpu(); - - for_each_cpu(i, &tsk->cpus_mask) { - if (cpu_data(i).smt_active == true) { - put_cpu(); - return -EINVAL; - } - } - set_ti_thread_flag(&tsk->thread_info, TIF_SPEC_L1D_FLUSH); - put_cpu(); - return ret; + return 0; } int disable_l1d_flush_for_task(struct task_struct *tsk) @@ -358,13 +345,31 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next, local_irq_restore(flags); } +/* + * Sent to a task that opts into L1D flushing via the prctl interface + * but ends up running on an SMT enabled core. + */ +static void l1d_flush_kill(struct callback_head *ch) +{ + force_sig(SIGBUS); +} + static inline unsigned long mm_mangle_tif_spec_bits(struct task_struct *next) { unsigned long next_tif = task_thread_info(next)->flags; unsigned long spec_bits = (next_tif >> TIF_SPEC_IB) & LAST_USER_MM_SPEC_MASK; + unsigned long next_mm; BUILD_BUG_ON(TIF_SPEC_L1D_FLUSH != TIF_SPEC_IB + 1); - return (unsigned long)next->mm | spec_bits; + next_mm = (unsigned long)next->mm | spec_bits; + + if ((next_mm & LAST_USER_MM_L1D_FLUSH) && this_cpu_read(cpu_info.smt_active)) { + clear_ti_thread_flag(&next->thread_info, TIF_SPEC_L1D_FLUSH); + next->l1d_flush_kill.func = l1d_flush_kill; + task_work_add(next, &next->l1d_flush_kill, true); + } + + return next_mm; } static void cond_mitigation(struct task_struct *next) diff --git a/include/linux/sched.h b/include/linux/sched.h index 322ea9b827e1..c569c49715d7 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1338,6 +1338,16 @@ struct task_struct { unsigned long getblk_bh_state; #endif +#ifdef CONFIG_ARCH_HAS_PARANOID_L1D_FLUSH + /* + * If L1D flush is supported on mm context switch + * then we use this callback head to queue kill work + * to kill tasks that are not running on SMT disabled + * cores + */ + struct callback_head l1d_flush_kill; +#endif + /* * New fields for task_struct should be added above here, so that * they are included in the randomized portion of task_struct. -- 2.17.1