[Xen-devel] Re: [PATCH FIXED] x86: use flush_tlb_others to implement flush_tlb_all

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

Huh.  How's this?

        J


Subject: [PATCH] x86: use flush_tlb_others to implement flush_tlb_all

Use the flush_tlb_others() call to implement flush_tlb_all().  This is
useful because flush_tlb_others() already goes via paravirt_ops, and so
will be properly paravirtualized.  This needs a small extension of the
extension to the existing native_flush_tlb_others: the global flush is
indicated by setting the "mm" parameter to NULL, so that kernel mappings
are also flushed.

As a side effect of this change, we need to initialize
native_flush_tlb_others()'s spinlocks earlier, as flush_tlb_all() can
be called earlier in the boot sequence.

(Nothing similar is required for xen_flush_tlb_others, as we don't use
global mappings in a guest-visible way under Xen.)

[ Impact: Optimise flush_tlb_all under Xen ]
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>

diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index 16a5c84..4b663c5 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -89,6 +89,10 @@ static inline void __flush_tlb_one(unsigned long addr)

#ifndef CONFIG_SMP

+static inline void __init init_smp_flush(void)
+{
+}
+
#define flush_tlb() __flush_tlb()
#define flush_tlb_all() __flush_tlb_all()
#define local_flush_tlb() __flush_tlb()
@@ -129,6 +133,8 @@ static inline void reset_lazy_tlbstate(void)

#define local_flush_tlb() __flush_tlb()

+extern void init_smp_flush(void);
+
extern void flush_tlb_all(void);
extern void flush_tlb_current_task(void);
extern void flush_tlb_mm(struct mm_struct *);
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index b415843..747566c 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -87,6 +87,7 @@
#include <asm/cacheflush.h>
#include <asm/processor.h>
#include <asm/bugs.h>
+#include <asm/tlbflush.h>

#include <asm/system.h>
#include <asm/vsyscall.h>
@@ -906,6 +907,9 @@ void __init setup_arch(char **cmdline_p)

        initmem_init(0, max_pfn);

+       /* Initialize cross-cpu tlb flushes */
+       init_smp_flush();
+
#ifdef CONFIG_ACPI_SLEEP
        /*
         * Reserve low memory region for sleep support.
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 821e970..efd9109 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -147,13 +147,25 @@ void smp_invalidate_interrupt(struct pt_regs *regs)
                 * BUG();
                 */

-       if (f->flush_mm == percpu_read(cpu_tlbstate.active_mm)) {
-               if (percpu_read(cpu_tlbstate.state) == TLBSTATE_OK) {
+       if (f->flush_mm == NULL ||
+           f->flush_mm == percpu_read(cpu_tlbstate.active_mm)) {
+               int tlbstate = percpu_read(cpu_tlbstate.state);
+
+		/* 
+		 * flush_mm == NULL means flush everything, including
+                * global tlbs, which will only happen when flushing
+		 * kernel mappings. 
+		 */
+               if (f->flush_mm == NULL)
+                       __flush_tlb_all();
+               else if (tlbstate == TLBSTATE_OK) {
                        if (f->flush_va == TLB_FLUSH_ALL)
                                local_flush_tlb();
                        else
                                __flush_tlb_one(f->flush_va);
-               } else
+               }
+
+               if (tlbstate == TLBSTATE_LAZY)
                        leave_mm(cpu);
        }
out:
@@ -217,16 +229,13 @@ void native_flush_tlb_others(const struct cpumask 
*cpumask,
        flush_tlb_others_ipi(cpumask, mm, va);
}

-static int __cpuinit init_smp_flush(void)
+void __init init_smp_flush(void)
{
        int i;

        for (i = 0; i < ARRAY_SIZE(flush_state); i++)
                spin_lock_init(&flush_state[i].tlbstate_lock);
-
-       return 0;
}
-core_initcall(init_smp_flush);

void flush_tlb_current_task(void)
{
@@ -275,16 +284,16 @@ void flush_tlb_page(struct vm_area_struct *vma, unsigned 
long va)
        preempt_enable();
}

-static void do_flush_tlb_all(void *info)
+void flush_tlb_all(void)
{
-       unsigned long cpu = smp_processor_id();
+       /* flush_tlb_others expects preempt to be disabled */
+       get_cpu();
+
+       flush_tlb_others(cpu_online_mask, NULL, TLB_FLUSH_ALL);

        __flush_tlb_all();
        if (percpu_read(cpu_tlbstate.state) == TLBSTATE_LAZY)
-               leave_mm(cpu);
-}
+               leave_mm(smp_processor_id());

-void flush_tlb_all(void)
-{
-       on_each_cpu(do_flush_tlb_all, NULL, 1);
+       put_cpu();
}
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index 760e3a5..42aa664 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -1284,6 +1284,13 @@ static void xen_flush_tlb_single(unsigned long addr)
        preempt_enable();
}

+/* 
+ * Flush tlb on other cpus.  Xen can do this via a single hypercall
+ * rather than explicit IPIs, which has the nice property of avoiding
+ * any cpus which don't actually have dirty tlbs.  Unfortunately it
+ * doesn't give us an opportunity to kick out cpus which are in lazy
+ * tlb state, so we may end up reflushing some cpus unnecessarily.
+ */
static void xen_flush_tlb_others(const struct cpumask *cpus,
                                 struct mm_struct *mm, unsigned long va)
{



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