x86/mm/tlb: Remove 'struct flush_tlb_info' from the stack

Move flush_tlb_info variables off the stack. This allows to align
flush_tlb_info to cache-line and avoid potentially unnecessary cache
line movements. It also allows to have a fixed virtual-to-physical
translation of the variables, which reduces TLB misses.

Use per-CPU struct for flush_tlb_mm_range() and
flush_tlb_kernel_range(). Add debug assertions to ensure there are
no nested TLB flushes that might overwrite the per-CPU data. For
arch_tlbbatch_flush() use a const struct.

Results when running a microbenchmarks that performs 10^6 MADV_DONTEED
operations and touching a page, in which 3 additional threads run a
busy-wait loop (5 runs, PTI and retpolines are turned off):

			base		off-stack
			----		---------
  avg (usec/op)		1.629		1.570	(-3%)
  stddev		0.014		0.009

Signed-off-by: Nadav Amit <namit@vmware.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20190425230143.7008-1-namit@vmware.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 487b8474c01cde006241a4c9a732bfe6aae53ff6..7f61431c75fb7bbbf5189525d1c242ce25ba57f9 100644 (file)
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -634,7 +634,7 @@ static void flush_tlb_func_common(const struct flush_tlb_info *f,
        this_cpu_write(cpu_tlbstate.ctxs[loaded_mm_asid].tlb_gen, mm_tlb_gen);
 }
 
-static void flush_tlb_func_local(void *info, enum tlb_flush_reason reason)
+static void flush_tlb_func_local(const void *info, enum tlb_flush_reason reason)
 {
        const struct flush_tlb_info *f = info;
 
@@ -722,43 +722,81 @@ void native_flush_tlb_others(const struct cpumask *cpumask,
  */
 unsigned long tlb_single_page_flush_ceiling __read_mostly = 33;
 
+static DEFINE_PER_CPU_SHARED_ALIGNED(struct flush_tlb_info, flush_tlb_info);
+
+#ifdef CONFIG_DEBUG_VM
+static DEFINE_PER_CPU(unsigned int, flush_tlb_info_idx);
+#endif
+
+static inline struct flush_tlb_info *get_flush_tlb_info(struct mm_struct *mm,
+                       unsigned long start, unsigned long end,
+                       unsigned int stride_shift, bool freed_tables,
+                       u64 new_tlb_gen)
+{
+       struct flush_tlb_info *info = this_cpu_ptr(&flush_tlb_info);
+
+#ifdef CONFIG_DEBUG_VM
+       /*
+        * Ensure that the following code is non-reentrant and flush_tlb_info
+        * is not overwritten. This means no TLB flushing is initiated by
+        * interrupt handlers and machine-check exception handlers.
+        */
+       BUG_ON(this_cpu_inc_return(flush_tlb_info_idx) != 1);
+#endif
+
+       info->start             = start;
+       info->end               = end;
+       info->mm                = mm;
+       info->stride_shift      = stride_shift;
+       info->freed_tables      = freed_tables;
+       info->new_tlb_gen       = new_tlb_gen;
+
+       return info;
+}
+
+static inline void put_flush_tlb_info(void)
+{
+#ifdef CONFIG_DEBUG_VM
+       /* Complete reentrency prevention checks */
+       barrier();
+       this_cpu_dec(flush_tlb_info_idx);
+#endif
+}
+
 void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
                                unsigned long end, unsigned int stride_shift,
                                bool freed_tables)
 {
+       struct flush_tlb_info *info;
+       u64 new_tlb_gen;
        int cpu;
 
-       struct flush_tlb_info info = {
-               .mm = mm,
-               .stride_shift = stride_shift,
-               .freed_tables = freed_tables,
-       };
-
        cpu = get_cpu();
 
-       /* This is also a barrier that synchronizes with switch_mm(). */
-       info.new_tlb_gen = inc_mm_tlb_gen(mm);
-
        /* Should we flush just the requested range? */
-       if ((end != TLB_FLUSH_ALL) &&
-           ((end - start) >> stride_shift) <= tlb_single_page_flush_ceiling) {
-               info.start = start;
-               info.end = end;
-       } else {
-               info.start = 0UL;
-               info.end = TLB_FLUSH_ALL;
+       if ((end == TLB_FLUSH_ALL) ||
+           ((end - start) >> stride_shift) > tlb_single_page_flush_ceiling) {
+               start = 0;
+               end = TLB_FLUSH_ALL;
        }
 
+       /* This is also a barrier that synchronizes with switch_mm(). */
+       new_tlb_gen = inc_mm_tlb_gen(mm);
+
+       info = get_flush_tlb_info(mm, start, end, stride_shift, freed_tables,
+                                 new_tlb_gen);
+
        if (mm == this_cpu_read(cpu_tlbstate.loaded_mm)) {
-               VM_WARN_ON(irqs_disabled());
+               lockdep_assert_irqs_enabled();
                local_irq_disable();
-               flush_tlb_func_local(&info, TLB_LOCAL_MM_SHOOTDOWN);
+               flush_tlb_func_local(info, TLB_LOCAL_MM_SHOOTDOWN);
                local_irq_enable();
        }
 
        if (cpumask_any_but(mm_cpumask(mm), cpu) < nr_cpu_ids)
-               flush_tlb_others(mm_cpumask(mm), &info);
+               flush_tlb_others(mm_cpumask(mm), info);
 
+       put_flush_tlb_info();
        put_cpu();
 }
 
@@ -787,38 +825,48 @@ static void do_kernel_range_flush(void *info)
 
 void flush_tlb_kernel_range(unsigned long start, unsigned long end)
 {
-
        /* Balance as user space task's flush, a bit conservative */
        if (end == TLB_FLUSH_ALL ||
            (end - start) > tlb_single_page_flush_ceiling << PAGE_SHIFT) {
                on_each_cpu(do_flush_tlb_all, NULL, 1);
        } else {
-               struct flush_tlb_info info;
-               info.start = start;
-               info.end = end;
-               on_each_cpu(do_kernel_range_flush, &info, 1);
+               struct flush_tlb_info *info;
+
+               preempt_disable();
+               info = get_flush_tlb_info(NULL, start, end, 0, false, 0);
+
+               on_each_cpu(do_kernel_range_flush, info, 1);
+
+               put_flush_tlb_info();
+               preempt_enable();
        }
 }
 
+/*
+ * arch_tlbbatch_flush() performs a full TLB flush regardless of the active mm.
+ * This means that the 'struct flush_tlb_info' that describes which mappings to
+ * flush is actually fixed. We therefore set a single fixed struct and use it in
+ * arch_tlbbatch_flush().
+ */
+static const struct flush_tlb_info full_flush_tlb_info = {
+       .mm = NULL,
+       .start = 0,
+       .end = TLB_FLUSH_ALL,
+};
+
 void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch)
 {
-       struct flush_tlb_info info = {
-               .mm = NULL,
-               .start = 0UL,
-               .end = TLB_FLUSH_ALL,
-       };
-
        int cpu = get_cpu();
 
        if (cpumask_test_cpu(cpu, &batch->cpumask)) {
-               VM_WARN_ON(irqs_disabled());
+               lockdep_assert_irqs_enabled();
                local_irq_disable();
-               flush_tlb_func_local(&info, TLB_LOCAL_SHOOTDOWN);
+               flush_tlb_func_local(&full_flush_tlb_info, TLB_LOCAL_SHOOTDOWN);
                local_irq_enable();
        }
 
        if (cpumask_any_but(&batch->cpumask, cpu) < nr_cpu_ids)
-               flush_tlb_others(&batch->cpumask, &info);
+               flush_tlb_others(&batch->cpumask, &full_flush_tlb_info);
 
        cpumask_clear(&batch->cpumask);