um: implement flush_cache_vmap/flush_cache_vunmap

vmalloc() heavy workloads in UML are extremely slow, due to
flushing the entire kernel VM space (flush_tlb_kernel_vm())
on the first segfault.

Implement flush_cache_vmap() to avoid that, and while at it
also add flush_cache_vunmap() since it's trivial.

This speeds up my vmalloc() heavy test of copying files out
from /sys/kernel/debug/gcov/ by 30x (from 30s to 1s.)
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Acked-By: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/include/asm/cacheflush.h

+#ifndef __UM_ASM_CACHEFLUSH_H
+#define __UM_ASM_CACHEFLUSH_H
+
+#include <asm/tlbflush.h>
+#define flush_cache_vmap flush_tlb_kernel_range
+#define flush_cache_vunmap flush_tlb_kernel_range
+
+#include <asm-generic/cacheflush.h>
+#endif /* __UM_ASM_CACHEFLUSH_H */

arch/um/include/asm/tlb.h

@@ -5,7 +5,7 @@
 #include <linux/mm.h>
 
 #include <asm/tlbflush.h>
-#include <asm-generic/cacheflush.h>
+#include <asm/cacheflush.h>
 #include <asm-generic/tlb.h>
 
 #endif