base_hw & arm_v7: Use write-back caching.

Add 'resume_faulter' syscall that is similar to 'resume_thread', but
is called only when resuming a thread after resolving its pagefault.
This way the kernel can flush caches after resolving a pagefault. This is
because by now the MMU doesn't use caches when doing a pagetable walk.

base-hw/include/kernel/syscalls.h

@@ -39,6 +39,7 @@ namespace Kernel
 		START_THREAD = 2,
 		PAUSE_THREAD = 3,
 		RESUME_THREAD = 4,
+		RESUME_FAULTER = 28,
 		GET_THREAD = 5,
 		CURRENT_THREAD_ID = 6,
 		YIELD_THREAD = 7,
@@ -247,6 +248,15 @@ namespace Kernel
 	{ return syscall(RESUME_THREAD, id); }
 
 
+	/**
+	 * Continue thread after a pagefault that could be resolved
+	 *
+	 * \param id  ID of the targeted thread
+	 */
+	inline void resume_faulter(unsigned long const id = 0) {
+		syscall(RESUME_FAULTER, id); }
+
+
 	/**
 	 * Let the current thread give up its remaining timeslice
 	 *

base-hw/src/core/include/arm/section_table.h

@@ -154,7 +154,7 @@ namespace Arm
 			    return Tex::bits(2) | C::bits(0) | B::bits(0);
 		if(cache_support()) {
 			if(Page_flags::C::get(flags))
-				return Tex::bits(6) | C::bits(1) | B::bits(0);
+				return Tex::bits(5) | C::bits(0) | B::bits(1);
 			    return Tex::bits(4) | C::bits(0) | B::bits(0);
 		}
 		        return Tex::bits(4) | C::bits(0) | B::bits(0);

base-hw/src/core/kernel.cc

@@ -1726,6 +1726,31 @@ namespace Kernel
 	}
 
 
+	/**
+	 * Do specific syscall for 'user', for details see 'syscall.h'
+	 */
+	void do_resume_faulter(Thread * const user)
+	{
+		/* get targeted thread */
+		Thread * const t = Thread::pool()->object(user->user_arg_1());
+		assert(t);
+
+		/* check permissions */
+		assert(user->pd_id() == core_id() || user->pd_id() == t->pd_id());
+
+		/*
+		 * Writeback the TLB entry that resolves the fault.
+		 * This is a substitution for write-through-flagging
+		 * the memory that holds the TLB data, because the latter
+		 * is not feasible in core space.
+		 */
+		Cpu::flush_caches();
+
+		/* resume targeted thread */
+		t->resume();
+	}
+
+
 	/**
 	 * Do specific syscall for 'user', for details see 'syscall.h'
 	 */
@@ -2075,6 +2100,7 @@ namespace Kernel
 			/* 25         */ do_run_vm,
 			/* 26         */ do_delete_thread,
 			/* 27         */ do_signal_pending,
+			/* 28         */ do_resume_faulter,
 		};
 		enum { MAX_SYSCALL = sizeof(handle_sysc)/sizeof(handle_sysc[0]) - 1 };
 

base-hw/src/core/rm_session_support.cc

@@ -80,8 +80,8 @@ void Ipc_pager::resolve_and_wait_for_fault()
 		                              _mapping.size_log2, flags, space);
 		assert(!sl2);
 	}
-	/* try to wake up faulter */
-	assert(!Kernel::resume_thread(_pagefault.thread_id));
+	/* wake up faulter */
+	Kernel::resume_faulter(_pagefault.thread_id);
 
 	/* wait for next page fault */
 	wait_for_fault();