Allow ddb and dtrace use the DMAP region on arm64

When writing to memory on arm64 we may be trying to be accessing a
read-only page. In this case try to access via the DMAP region to
get a writable location.

While here simplify writing data in DDB and stop trashing the size as
it is passed into the cache handling functions.

Sponsored by:	The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D32053

sys/arm64/arm64/db_interface.c

@@ -153,40 +153,25 @@ db_write_bytes(vm_offset_t addr, size_t size, char *data)
 	jmp_buf jb;
 	void *prev_jb;
 	char *dst;
+	size_t i;
 	int ret;
-	uint64_t tmp64;
-	uint32_t tmp32;
-	uint16_t tmp16;
 
 	prev_jb = kdb_jmpbuf(jb);
 	ret = setjmp(jb);
 	if (ret == 0) {
-		if (size == 8 && (addr & 7) == 0) {
-			dst = (char *)&tmp64;
-			while (size-- > 0)
-				*dst++ = *data++;
-			*((uint64_t *)addr) = tmp64;
-		} else if (size == 4 && (addr & 3) == 0) {
-			dst = (char *)&tmp32;
-			while (size-- > 0)
-				*dst++ = *data++;
-			*((uint32_t *)addr) = tmp32;
-		} else if (size == 2 && (addr & 1) == 0) {
-			dst = (char *)&tmp16;
-			while (size-- > 0)
-				*dst++ = *data++;
-			*((uint32_t *)addr) = tmp16;
+		if (!arm64_get_writable_addr(addr, &addr)) {
+			ret = 1;
 		} else {
 			dst = (char *)addr;
-			while (size-- > 0)
+			for (i = 0; i < size; i++)
 				*dst++ = *data++;
-		}
 			dsb(ish);
 
 			/* Clean D-cache and invalidate I-cache */
 			cpu_dcache_wb_range(addr, (vm_size_t)size);
 			cpu_icache_sync_range(addr, (vm_size_t)size);
 		}
+	}
 	(void)kdb_jmpbuf(prev_jb);
 
 	return (ret);

sys/arm64/arm64/machdep.c

@@ -942,6 +942,42 @@ init_proc0(vm_offset_t kstack)
 	serror_enable();
 }
 
+/*
+ * Get an address to be used to write to kernel data that may be mapped
+ * read-only, e.g. to patch kernel code.
+ */
+bool
+arm64_get_writable_addr(vm_offset_t addr, vm_offset_t *out)
+{
+	vm_paddr_t pa;
+
+	/* Check if the page is writable */
+	if (PAR_SUCCESS(arm64_address_translate_s1e1w(addr))) {
+		*out = addr;
+		return (true);
+	}
+
+	/*
+	 * Find the physical address of the given page.
+	 */
+	if (!pmap_klookup(addr, &pa)) {
+		return (false);
+	}
+
+	/*
+	 * If it is within the DMAP region and is writable use that.
+	 */
+	if (PHYS_IN_DMAP(pa)) {
+		addr = PHYS_TO_DMAP(pa);
+		if (PAR_SUCCESS(arm64_address_translate_s1e1w(addr))) {
+			*out = addr;
+			return (true);
+		}
+	}
+
+	return (false);
+}
+
 typedef struct {
 	uint32_t type;
 	uint64_t phys_start;

sys/arm64/include/cpufunc.h

@@ -246,6 +246,7 @@ int arm64_icache_sync_range_checked(vm_offset_t, vm_size_t);
 void arm64_dcache_wbinv_range(vm_offset_t, vm_size_t);
 void arm64_dcache_inv_range(vm_offset_t, vm_size_t);
 void arm64_dcache_wb_range(vm_offset_t, vm_size_t);
+bool arm64_get_writable_addr(vm_offset_t, vm_offset_t *);
 
 #endif	/* _KERNEL */
 #endif	/* _MACHINE_CPUFUNC_H_ */

sys/cddl/dev/fbt/aarch64/fbt_isa.c

@@ -74,8 +74,12 @@ fbt_invop(uintptr_t addr, struct trapframe *frame, uintptr_t rval)
 void
 fbt_patch_tracepoint(fbt_probe_t *fbt, fbt_patchval_t val)
 {
+	vm_offset_t addr;
 
-	*fbt->fbtp_patchpoint = val;
+	if (!arm64_get_writable_addr((vm_offset_t)fbt->fbtp_patchpoint, &addr))
+		panic("%s: Unable to write new instruction", __func__);
+
+	*(fbt_patchval_t *)addr = val;
 	cpu_icache_sync_range((vm_offset_t)fbt->fbtp_patchpoint, 4);
 }