arch, mm: Remove tlb_fast_mode()

Since the introduction of preemptible mmu_gather TLB fast mode has been
broken. TLB fast mode relies on there being absolutely no concurrency;
it frees pages first and invalidates TLBs later.

However now we can get concurrency and stuff goes *bang*.

This patch removes all tlb_fast_mode() code; it was found the better
option vs trying to patch the hole by entangling tlb invalidation with
the scheduler.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Tony Luck <tony.luck@intel.com>
Reported-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 23 deletions

diff --git a/arch/arm/include/asm/tlb.h b/arch/arm/include/asm/tlb.h
index 99a19512ee26..bdf2b8458ec1 100644
--- a/arch/arm/include/asm/tlb.h
+++ b/arch/arm/include/asm/tlb.h
@@ -33,18 +33,6 @@
 #include <asm/pgalloc.h>
 #include <asm/tlbflush.h>
 
-/*
- * We need to delay page freeing for SMP as other CPUs can access pages
- * which have been removed but not yet had their TLB entries invalidated.
- * Also, as ARMv7 speculative prefetch can drag new entries into the TLB,
- * we need to apply this same delaying tactic to ensure correct operation.
- */
-#if defined(CONFIG_SMP) || defined(CONFIG_CPU_32v7)
-#define tlb_fast_mode(tlb)      0
-#else
-#define tlb_fast_mode(tlb)      1
-#endif
-
 #define MMU_GATHER_BUNDLE       8
 
 /*
@@ -112,12 +100,10 @@ static inline void __tlb_alloc_page(struct mmu_gather *tlb)
 static inline void tlb_flush_mmu(struct mmu_gather *tlb)
 {
         tlb_flush(tlb);
-        if (!tlb_fast_mode(tlb)) {
-                free_pages_and_swap_cache(tlb->pages, tlb->nr);
-                tlb->nr = 0;
-                if (tlb->pages == tlb->local)
-                        __tlb_alloc_page(tlb);
-        }
+        free_pages_and_swap_cache(tlb->pages, tlb->nr);
+        tlb->nr = 0;
+        if (tlb->pages == tlb->local)
+                __tlb_alloc_page(tlb);
 }
 
 static inline void
@@ -178,11 +164,6 @@ tlb_end_vma(struct mmu_gather *tlb, struct vm_area_struct *vma)
 
 static inline int __tlb_remove_page(struct mmu_gather *tlb, struct page *page)
 {
-        if (tlb_fast_mode(tlb)) {
-                free_page_and_swap_cache(page);
-                return 1; /* avoid calling tlb_flush_mmu */
-        }
-
         tlb->pages[tlb->nr++] = page;
         VM_BUG_ON(tlb->nr > tlb->max);
         return tlb->max - tlb->nr;