images/farmem: add driver for adding memory region to kernel

Co-authored-by: Jonas Kaufmann <jokau03@gmail.com>

.gitignore

@@ -23,6 +23,9 @@ sims/net/menshen/obj_dir
 sims/net/tofino/tofino
 doc/doxygen
 doc/_build
+images/farmem/Module.symvers
+images/farmem/modules.order
+images/farmem/farmem.mod*
 images/kernel/kheaders/
 images/mqnic/Module.symvers
 images/mqnic/modules.order

images/farmem/CPPLINT.cfg

+exclude_files=.*

images/farmem/Makefile

+obj-m += farmem.o
+farmem-objs += farmem_main.o

images/farmem/farmem_main.c

+#include <linux/kernel.h>
+#include <linux/memory_hotplug.h>
+#include <linux/module.h>
+#include <linux/pfn_t.h>
+#include <linux/vmalloc.h>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Antoine Kaufmann");
+MODULE_DESCRIPTION(
+    "Manually exposes specified memory region in the specified "
+    "numa node.");
+MODULE_VERSION("0.1");
+
+static unsigned long base_addr = 0;
+static unsigned long size = 0;
+static int nnid = 1;
+static bool drain_node = false;
+
+module_param(base_addr, ulong, 0);
+module_param(size, ulong, 0);
+module_param(nnid, int, 0);
+module_param(drain_node, bool, 0);
+
+/**
+ * drains all available memory from the specified numa node by allocating (and
+ * leaking) it
+ */
+static void do_drain_node(int nid) {
+  unsigned long eaten;
+  struct page *p;
+
+  printk(KERN_INFO "draining node %d\n", nid);
+  if (nid == 0) {
+    printk(KERN_ALERT "draining node 0 is probably a bad idea\n");
+  }
+
+  /* start with large chunks and move to smaller ones */
+  eaten = 0;
+  do {
+    p = alloc_pages_node(
+        nid,
+        GFP_KERNEL | __GFP_NOWARN | __GFP_NORETRY | GFP_NOWAIT | __GFP_THISNODE,
+        0);
+    if (p)
+      eaten += PAGE_SIZE;
+  }
+  /* Local memory is drained before farmem, therefore the following works.
+     Tested on kernel 5.15.69.*/
+  while (p && pfn_t_to_phys(page_to_pfn_t(p)) < base_addr);
+
+  printk(KERN_INFO "drained %lu bytes\n", eaten);
+}
+
+static int __init farmem_mod_init(void) {
+  int rc;
+
+  printk(KERN_ALERT "Loading farmem driver\n");
+  if (!base_addr || !size) {
+    panic("base address and length must be set");
+  }
+
+  if (!node_possible(nnid)) {
+    panic("invalid numa node spcified");
+  }
+
+  if (drain_node)
+    do_drain_node(nnid);
+
+  rc = add_memory_driver_managed(nnid, base_addr, size, "System RAM (farmem)",
+                                 MHP_NONE);
+  if (rc) {
+    printk(KERN_ALERT "adding memory failed: %d\n", rc);
+  }
+  node_set_online(nnid);
+
+  /* Some local memory still remains usable, drain again to get it all. */
+  if (drain_node)
+    do_drain_node(nnid);
+
+  return 0;
+}
+
+static void __exit farmem_mod_exit(void) {
+  printk(KERN_ALERT "Unloading farmem driver, this is broken\n");
+}
+
+module_init(farmem_mod_init);
+module_exit(farmem_mod_exit);

images/rules.mk

@@ -50,13 +50,16 @@ kheader_dir := $(d)kernel/kheaders
 kheader_tar := $(d)kheaders.tar.bz2
 mqnic_dir := $(d)mqnic
 mqnic_mod := $(mqnic_dir)/mqnic.ko
+farmem_dir := $(d)farmem
+farmem_mod := $(farmem_dir)/farmem.ko
 m5_bin := $(d)m5
 guest_init := $(d)/scripts/guestinit.sh
 
-build-images: $(IMAGES) $(RAW_IMAGES) $(vmlinux) $(bz_image) $(mqnic_mod)
+build-images: $(IMAGES) $(RAW_IMAGES) $(vmlinux) $(bz_image) $(mqnic_mod) \
+  $(farmem_mod)
 
 build-images-min: $(IMAGES_MIN) $(RAW_IMAGES_MIN) $(vmlinux) $(bz_image) \
-    $(mqnic_mod)
+    $(mqnic_mod) $(farmem_mod)
 
 # only converts existing images to raw
 convert-images-raw:
@@ -180,10 +183,17 @@ $(mqnic_mod): $(vmlinux)
 	$(MAKE) -C $(kernel_dir) M=$(abspath $(mqnic_dir)) modules
 	touch $@
 
+################################################
+# farmem kernel module
 
-CLEAN := $(addprefix $(d), mqnic/mqnic.ko mqnic/*.o mqnic/.*.cmd mqnic/*.mod \
-    mqnic/mqnic.mod.c mqnic/Module.symvers mqnic/modules.order)
+$(farmem_mod): $(vmlinux)
+	$(MAKE) -C $(kernel_dir) M=$(abspath $(farmem_dir)) modules
+	touch $@
 
+CLEAN := $(addprefix $(d), mqnic/mqnic.ko mqnic/*.o mqnic/.*.cmd mqnic/*.mod \
+    mqnic/mqnic.mod.c mqnic/Module.symvers mqnic/modules.order \
+    farmem/farmem.ko farmem/*.o farmem/.*.cmd farmem/*.mod \
+    farmem/farmem.mod.c farmem/Module.symvers farmem/modules.order)
 DISTCLEAN := $(kernel_dir) $(packer) $(bz_image) $(vmlinux) $(kheader_dir) \
     $(foreach i,$(IMAGES),$(dir $(i)) $(subst output-,input-,$(dir $(i)))) \
     $(d)packer_cache $(d)kheaders.tar.bz2