x86/mm/tlb: Flush remote and local TLBs concurrently

To improve TLB shootdown performance, flush the remote and local TLBs
concurrently. Introduce flush_tlb_multi() that does so. Introduce
paravirtual versions of flush_tlb_multi() for KVM, Xen and hyper-v (Xen
and hyper-v are only compile-tested).

While the updated smp infrastructure is capable of running a function on
a single local core, it is not optimized for this case. The multiple
function calls and the indirect branch introduce some overhead, and
might make local TLB flushes slower than they were before the recent
changes.

Before calling the SMP infrastructure, check if only a local TLB flush
is needed to restore the lost performance in this common case. This
requires to check mm_cpumask() one more time, but unless this mask is
updated very frequently, this should impact performance negatively.

Signed-off-by: Nadav Amit <namit@vmware.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Michael Kelley <mikelley@microsoft.com> # Hyper-v parts
Reviewed-by: Juergen Gross <jgross@suse.com> # Xen and paravirt parts
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/r/20210220231712.2475218-5-namit@vmware.com

diff --git a/arch/x86/hyperv/mmu.c b/arch/x86/hyperv/mmu.c
index 2c87350c1fb095149a06709cbc0b11f2427f7acc..681dba8de4f2385c13735721eb5ef49b565c1a5e 100644 (file)
--- a/arch/x86/hyperv/mmu.c
+++ b/arch/x86/hyperv/mmu.c
@@ -52,8 +52,8 @@ static inline int fill_gva_list(u64 gva_list[], int offset,
        return gva_n - offset;
 }
 
-static void hyperv_flush_tlb_others(const struct cpumask *cpus,
-                                   const struct flush_tlb_info *info)
+static void hyperv_flush_tlb_multi(const struct cpumask *cpus,
+                                  const struct flush_tlb_info *info)
 {
        int cpu, vcpu, gva_n, max_gvas;
        struct hv_tlb_flush **flush_pcpu;
@@ -61,7 +61,7 @@ static void hyperv_flush_tlb_others(const struct cpumask *cpus,
        u64 status = U64_MAX;
        unsigned long flags;
 
-       trace_hyperv_mmu_flush_tlb_others(cpus, info);
+       trace_hyperv_mmu_flush_tlb_multi(cpus, info);
 
        if (!hv_hypercall_pg)
                goto do_native;
@@ -164,7 +164,7 @@ check_status:
        if (!(status & HV_HYPERCALL_RESULT_MASK))
                return;
 do_native:
-       native_flush_tlb_others(cpus, info);
+       native_flush_tlb_multi(cpus, info);
 }
 
 static u64 hyperv_flush_tlb_others_ex(const struct cpumask *cpus,
@@ -239,6 +239,6 @@ void hyperv_setup_mmu_ops(void)
                return;
 
        pr_info("Using hypercall for remote TLB flush\n");
-       pv_ops.mmu.flush_tlb_others = hyperv_flush_tlb_others;
+       pv_ops.mmu.flush_tlb_multi = hyperv_flush_tlb_multi;
        pv_ops.mmu.tlb_remove_table = tlb_remove_table;
 }

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 4abf110e224380b2514626c8753eedabb7e4d905..45b55e3e063065d9658b06a4c027a0f431b481f1 100644 (file)
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -50,7 +50,7 @@ static inline void slow_down_io(void)
 void native_flush_tlb_local(void);
 void native_flush_tlb_global(void);
 void native_flush_tlb_one_user(unsigned long addr);
-void native_flush_tlb_others(const struct cpumask *cpumask,
+void native_flush_tlb_multi(const struct cpumask *cpumask,
                             const struct flush_tlb_info *info);
 
 static inline void __flush_tlb_local(void)
@@ -68,10 +68,10 @@ static inline void __flush_tlb_one_user(unsigned long addr)
        PVOP_VCALL1(mmu.flush_tlb_one_user, addr);
 }
 
-static inline void __flush_tlb_others(const struct cpumask *cpumask,
+static inline void __flush_tlb_multi(const struct cpumask *cpumask,
                                      const struct flush_tlb_info *info)
 {
-       PVOP_VCALL2(mmu.flush_tlb_others, cpumask, info);
+       PVOP_VCALL2(mmu.flush_tlb_multi, cpumask, info);
 }
 
 static inline void paravirt_tlb_remove_table(struct mmu_gather *tlb, void *table)

diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index de87087d3bde16ac6a062536ebad122541acc7ad..b7b35d5d58e738328970c698be9f9e7e6ad1dcb7 100644 (file)
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -188,8 +188,8 @@ struct pv_mmu_ops {
        void (*flush_tlb_user)(void);
        void (*flush_tlb_kernel)(void);
        void (*flush_tlb_one_user)(unsigned long addr);
-       void (*flush_tlb_others)(const struct cpumask *cpus,
-                                const struct flush_tlb_info *info);
+       void (*flush_tlb_multi)(const struct cpumask *cpus,
+                               const struct flush_tlb_info *info);
 
        void (*tlb_remove_table)(struct mmu_gather *tlb, void *table);
 

diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index a7a598af116db05691b9df9eb1b98bae2d015199..3c6681def912261a8bcf8c935ce092f3c448de34 100644 (file)
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -175,7 +175,7 @@ extern void initialize_tlbstate_and_flush(void);
  *  - flush_tlb_page(vma, vmaddr) flushes one page
  *  - flush_tlb_range(vma, start, end) flushes a range of pages
  *  - flush_tlb_kernel_range(start, end) flushes a range of kernel pages
- *  - flush_tlb_others(cpumask, info) flushes TLBs on other cpus
+ *  - flush_tlb_multi(cpumask, info) flushes TLBs on multiple cpus
  *
  * ..but the i386 has somewhat limited tlb flushing capabilities,
  * and page-granular flushes are available only on i486 and up.
@@ -209,7 +209,7 @@ struct flush_tlb_info {
 void flush_tlb_local(void);
 void flush_tlb_one_user(unsigned long addr);
 void flush_tlb_one_kernel(unsigned long addr);
-void flush_tlb_others(const struct cpumask *cpumask,
+void flush_tlb_multi(const struct cpumask *cpumask,
                      const struct flush_tlb_info *info);
 
 #ifdef CONFIG_PARAVIRT

diff --git a/arch/x86/include/asm/trace/hyperv.h b/arch/x86/include/asm/trace/hyperv.h
index 4d705cb4d63bed3ede763563a1cbe35b631b4c85..a8e5a7a2b46005f5a53c08423152d154b4bd309c 100644 (file)
--- a/arch/x86/include/asm/trace/hyperv.h
+++ b/arch/x86/include/asm/trace/hyperv.h
@@ -8,7 +8,7 @@
 
 #if IS_ENABLED(CONFIG_HYPERV)
 
-TRACE_EVENT(hyperv_mmu_flush_tlb_others,
+TRACE_EVENT(hyperv_mmu_flush_tlb_multi,
            TP_PROTO(const struct cpumask *cpus,
                     const struct flush_tlb_info *info),
            TP_ARGS(cpus, info),

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 5e78e01ca3b46f8eccfd11541850bc08a122b614..38ea9dee2456fe0420cc5a5940fc1779800c1437 100644 (file)
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -613,7 +613,7 @@ static int kvm_cpu_down_prepare(unsigned int cpu)
 }
 #endif
 
-static void kvm_flush_tlb_others(const struct cpumask *cpumask,
+static void kvm_flush_tlb_multi(const struct cpumask *cpumask,
                        const struct flush_tlb_info *info)
 {
        u8 state;
@@ -627,6 +627,11 @@ static void kvm_flush_tlb_others(const struct cpumask *cpumask,
         * queue flush_on_enter for pre-empted vCPUs
         */
        for_each_cpu(cpu, flushmask) {
+               /*
+                * The local vCPU is never preempted, so we do not explicitly
+                * skip check for local vCPU - it will never be cleared from
+                * flushmask.
+                */
                src = &per_cpu(steal_time, cpu);
                state = READ_ONCE(src->preempted);
                if ((state & KVM_VCPU_PREEMPTED)) {
@@ -636,7 +641,7 @@ static void kvm_flush_tlb_others(const struct cpumask *cpumask,
                }
        }
 
-       native_flush_tlb_others(flushmask, info);
+       native_flush_tlb_multi(flushmask, info);
 }
 
 static void __init kvm_guest_init(void)
@@ -654,7 +659,7 @@ static void __init kvm_guest_init(void)
        }
 
        if (pv_tlb_flush_supported()) {
-               pv_ops.mmu.flush_tlb_others = kvm_flush_tlb_others;
+               pv_ops.mmu.flush_tlb_multi = kvm_flush_tlb_multi;
                pv_ops.mmu.tlb_remove_table = tlb_remove_table;
                pr_info("KVM setup pv remote TLB flush\n");
        }

diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index c60222ab8ab9b8ae2dded7687609b3165020c544..197a1266215536d1c33310476b31232f04706458 100644 (file)
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -330,7 +330,7 @@ struct paravirt_patch_template pv_ops = {
        .mmu.flush_tlb_user     = native_flush_tlb_local,
        .mmu.flush_tlb_kernel   = native_flush_tlb_global,
        .mmu.flush_tlb_one_user = native_flush_tlb_one_user,
-       .mmu.flush_tlb_others   = native_flush_tlb_others,
+       .mmu.flush_tlb_multi    = native_flush_tlb_multi,
        .mmu.tlb_remove_table   =
                        (void (*)(struct mmu_gather *, void *))tlb_remove_page,
 

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 07b6701a540ae73898461359b23a7831bf8567cc..8db87cd92e6bbac2f7ba0134cef509429d9c809e 100644 (file)
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -24,7 +24,7 @@
 # define __flush_tlb_local             native_flush_tlb_local
 # define __flush_tlb_global            native_flush_tlb_global
 # define __flush_tlb_one_user(addr)    native_flush_tlb_one_user(addr)
-# define __flush_tlb_others(msk, info) native_flush_tlb_others(msk, info)
+# define __flush_tlb_multi(msk, info)  native_flush_tlb_multi(msk, info)
 #endif
 
 /*
@@ -490,7 +490,7 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
                /*
                 * Even in lazy TLB mode, the CPU should stay set in the
                 * mm_cpumask. The TLB shootdown code can figure out from
-                * from cpu_tlbstate.is_lazy whether or not to send an IPI.
+                * cpu_tlbstate.is_lazy whether or not to send an IPI.
                 */
                if (WARN_ON_ONCE(real_prev != &init_mm &&
                                 !cpumask_test_cpu(cpu, mm_cpumask(next))))
@@ -697,7 +697,7 @@ static void flush_tlb_func(void *info)
                 * garbage into our TLB.  Since switching to init_mm is barely
                 * slower than a minimal flush, just switch to init_mm.
                 *
-                * This should be rare, with native_flush_tlb_others skipping
+                * This should be rare, with native_flush_tlb_multi() skipping
                 * IPIs to lazy TLB mode CPUs.
                 */
                switch_mm_irqs_off(NULL, &init_mm, NULL);
@@ -795,9 +795,14 @@ static bool tlb_is_not_lazy(int cpu)
 
 static DEFINE_PER_CPU(cpumask_t, flush_tlb_mask);
 
-STATIC_NOPV void native_flush_tlb_others(const struct cpumask *cpumask,
+STATIC_NOPV void native_flush_tlb_multi(const struct cpumask *cpumask,
                                         const struct flush_tlb_info *info)
 {
+       /*
+        * Do accounting and tracing. Note that there are (and have always been)
+        * cases in which a remote TLB flush will be traced, but eventually
+        * would not happen.
+        */
        count_vm_tlb_event(NR_TLB_REMOTE_FLUSH);
        if (info->end == TLB_FLUSH_ALL)
                trace_tlb_flush(TLB_REMOTE_SEND_IPI, TLB_FLUSH_ALL);
@@ -816,8 +821,7 @@ STATIC_NOPV void native_flush_tlb_others(const struct cpumask *cpumask,
         * doing a speculative memory access.
         */
        if (info->freed_tables) {
-               smp_call_function_many(cpumask, flush_tlb_func,
-                              (void *)info, 1);
+               on_each_cpu_mask(cpumask, flush_tlb_func, (void *)info, true);
        } else {
                /*
                 * Although we could have used on_each_cpu_cond_mask(),
@@ -844,14 +848,14 @@ STATIC_NOPV void native_flush_tlb_others(const struct cpumask *cpumask,
                        if (tlb_is_not_lazy(cpu))
                                __cpumask_set_cpu(cpu, cond_cpumask);
                }
-               smp_call_function_many(cond_cpumask, flush_tlb_func, (void *)info, 1);
+               on_each_cpu_mask(cond_cpumask, flush_tlb_func, (void *)info, true);
        }
 }
 
-void flush_tlb_others(const struct cpumask *cpumask,
+void flush_tlb_multi(const struct cpumask *cpumask,
                      const struct flush_tlb_info *info)
 {
-       __flush_tlb_others(cpumask, info);
+       __flush_tlb_multi(cpumask, info);
 }
 
 /*
@@ -931,16 +935,20 @@ void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
        info = get_flush_tlb_info(mm, start, end, stride_shift, freed_tables,
                                  new_tlb_gen);
 
-       if (mm == this_cpu_read(cpu_tlbstate.loaded_mm)) {
+       /*
+        * flush_tlb_multi() is not optimized for the common case in which only
+        * a local TLB flush is needed. Optimize this use-case by calling
+        * flush_tlb_func_local() directly in this case.
+        */
+       if (cpumask_any_but(mm_cpumask(mm), cpu) < nr_cpu_ids) {
+               flush_tlb_multi(mm_cpumask(mm), info);
+       } else if (mm == this_cpu_read(cpu_tlbstate.loaded_mm)) {
                lockdep_assert_irqs_enabled();
                local_irq_disable();
                flush_tlb_func(info);
                local_irq_enable();
        }
 
-       if (cpumask_any_but(mm_cpumask(mm), cpu) < nr_cpu_ids)
-               flush_tlb_others(mm_cpumask(mm), info);
-
        put_flush_tlb_info();
        put_cpu();
 }
@@ -1152,16 +1160,20 @@ void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch)
        int cpu = get_cpu();
 
        info = get_flush_tlb_info(NULL, 0, TLB_FLUSH_ALL, 0, false, 0);
-       if (cpumask_test_cpu(cpu, &batch->cpumask)) {
+       /*
+        * flush_tlb_multi() is not optimized for the common case in which only
+        * a local TLB flush is needed. Optimize this use-case by calling
+        * flush_tlb_func_local() directly in this case.
+        */
+       if (cpumask_any_but(&batch->cpumask, cpu) < nr_cpu_ids) {
+               flush_tlb_multi(&batch->cpumask, info);
+       } else if (cpumask_test_cpu(cpu, &batch->cpumask)) {
                lockdep_assert_irqs_enabled();
                local_irq_disable();
                flush_tlb_func(info);
                local_irq_enable();
        }
 
-       if (cpumask_any_but(&batch->cpumask, cpu) < nr_cpu_ids)
-               flush_tlb_others(&batch->cpumask, info);
-
        cpumask_clear(&batch->cpumask);
 
        put_flush_tlb_info();

diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
index cf2ade864c3020be11927d71b67b636c75a0a3da..09b95c0e876ec1c98e90794741d21fa364db2ee2 100644 (file)
--- a/arch/x86/xen/mmu_pv.c
+++ b/arch/x86/xen/mmu_pv.c
@@ -1247,8 +1247,8 @@ static void xen_flush_tlb_one_user(unsigned long addr)
        preempt_enable();
 }
 
-static void xen_flush_tlb_others(const struct cpumask *cpus,
-                                const struct flush_tlb_info *info)
+static void xen_flush_tlb_multi(const struct cpumask *cpus,
+                               const struct flush_tlb_info *info)
 {
        struct {
                struct mmuext_op op;
@@ -1258,7 +1258,7 @@ static void xen_flush_tlb_others(const struct cpumask *cpus,
        const size_t mc_entry_size = sizeof(args->op) +
                sizeof(args->mask[0]) * BITS_TO_LONGS(num_possible_cpus());
 
-       trace_xen_mmu_flush_tlb_others(cpus, info->mm, info->start, info->end);
+       trace_xen_mmu_flush_tlb_multi(cpus, info->mm, info->start, info->end);
 
        if (cpumask_empty(cpus))
                return;         /* nothing to do */
@@ -1267,9 +1267,8 @@ static void xen_flush_tlb_others(const struct cpumask *cpus,
        args = mcs.args;
        args->op.arg2.vcpumask = to_cpumask(args->mask);
 
-       /* Remove us, and any offline CPUS. */
+       /* Remove any offline CPUs */
        cpumask_and(to_cpumask(args->mask), cpus, cpu_online_mask);
-       cpumask_clear_cpu(smp_processor_id(), to_cpumask(args->mask));
 
        args->op.cmd = MMUEXT_TLB_FLUSH_MULTI;
        if (info->end != TLB_FLUSH_ALL &&
@@ -2086,7 +2085,7 @@ static const struct pv_mmu_ops xen_mmu_ops __initconst = {
        .flush_tlb_user = xen_flush_tlb,
        .flush_tlb_kernel = xen_flush_tlb,
        .flush_tlb_one_user = xen_flush_tlb_one_user,
-       .flush_tlb_others = xen_flush_tlb_others,
+       .flush_tlb_multi = xen_flush_tlb_multi,
        .tlb_remove_table = tlb_remove_table,
 
        .pgd_alloc = xen_pgd_alloc,

diff --git a/include/trace/events/xen.h b/include/trace/events/xen.h
index 3b61b587e1371d784756999653cf55e3a0726b12..44a3f565264d931b1b9257ad4090e5182f322bb6 100644 (file)
--- a/include/trace/events/xen.h
+++ b/include/trace/events/xen.h
@@ -346,7 +346,7 @@ TRACE_EVENT(xen_mmu_flush_tlb_one_user,
            TP_printk("addr %lx", __entry->addr)
        );
 
-TRACE_EVENT(xen_mmu_flush_tlb_others,
+TRACE_EVENT(xen_mmu_flush_tlb_multi,
            TP_PROTO(const struct cpumask *cpus, struct mm_struct *mm,
                     unsigned long addr, unsigned long end),
            TP_ARGS(cpus, mm, addr, end),