[Qemu-devel] [PATCH 3/3] support readonly memory feature in qemu

[Liu Sheng <liusheng@linux.vnet.ibm.com>]

as readonly memory is support in kvm, this patch supports this feature
in qemu, mainly pluging the memory region with KVM_MEM_READONLY flag
to kvm.

this can be tested by a kernel module from the author of kvm readonly
memory slot:

static int rom_tester_probe(struct pci_dev *dev, const struct pci_device_id *id)
{
	struct resource *res = &dev->resource[PCI_ROM_RESOURCE];
	char buf[6];
	size_t rom_size;
	char * __iomem map;
	int i;

	if (res->flags & (IORESOURCE_ROM_SHADOW | IORESOURCE_ROM_COPY |
	      IORESOURCE_ROM_BIOS_COPY)) {
		dev_printk(KERN_INFO, &dev->dev, "skip ROM COPY.\n");
		return 0;
	}

	if (res->flags &
			(IORESOURCE_ROM_COPY | IORESOURCE_ROM_BIOS_COPY))
	dev_printk(KERN_INFO, &dev->dev, "rom tester\n");

	if (pci_enable_rom(dev)) {
		dev_printk(KERN_INFO, &dev->dev, "do not found Rom\n");
		goto exit;
	}

	map = pci_map_rom(dev, &rom_size);
	if (!map) {
		dev_printk(KERN_INFO, &dev->dev, "map rom fail.\n");
		goto disable_exit;
	}

	dev_printk(KERN_INFO, &dev->dev, "Rom map: %p [size: %lx], phsyc:%llx.\n",
		   map, rom_size, pci_resource_start(dev, PCI_ROM_RESOURCE));

	if (rom_size < 6) {
		printk("map size < 6.\n");
		goto unmap_exit;
	}

	printk("The first 6 bytes:\n");
	for (i = 0; i < 6; i++) {
		buf[i] = map[i];
		printk("%x ", buf[i]);
	}
	printk("\n\n");

	memcpy(map, "KVMKVM", 6);
	if (!memcmp(map, "KVMKVM", 6)) {
		printk("Rom Test: fail.\n");
		goto unmap_exit;
	}

	for (i = 0; i < 6; i++)
		if (buf[i] != ((char *)map)[i]) {
			printk("The %d byte is changed: %x -> %x.\n",
			       i, buf[i], map[i]);
			printk("Rom Test: fail.\n");
			goto unmap_exit;
		}

	printk("Rom Test: Okay.\n");

unmap_exit:
	pci_unmap_rom(dev, map);
disable_exit:
	pci_disable_rom(dev);
exit:
	return 0;
}

static DEFINE_PCI_DEVICE_TABLE(rom_tester_tbl) = {
	{ PCI_DEVICE(PCI_ANY_ID, PCI_ANY_ID)},

	{0,}						/* 0 terminated list. */
};
MODULE_DEVICE_TABLE(pci, rom_tester_tbl);

static struct pci_driver rom_tester = {
	.name		= "pci-rom-tester",
	.id_table	= rom_tester_tbl,
	.probe		= rom_tester_probe,
};

static int __init pci_rom_test_init(void)
{
	int rc;

	rc = pci_register_driver(&rom_tester);
	if (rc)
		return rc;

	return 0;
}

static void __exit pci_rom_test_exit(void)
{
	pci_unregister_driver(&rom_tester);
}

module_init(pci_rom_test_init);
module_exit(pci_rom_test_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>");

we test it with the rom of Intel 82540EM Gigabit Ethernet Controller.
0. start qemu:
    qemu-system-x86_64 -enable-kvm -m 1G -smp 2 -hda fedora16.qcow2 \
        -nic nic,model=e1000,vlan=1,macadrr=52:00:12:34:56 \
        -net user,vlan=1
1. unbind the device:
    echo "0000:00:03.0" > /sys/bus/pci/devices/0000\:00\:03.0/driver/unbind
2. install the test kernel module, here we name it write_rom:
    modprobe write_rom
3. print dmesg to verify the result is ok or fail:
    dmesg
4. remove the test kernel module.
    rmmod write_rom
5. rebind the device to its driver, test if the nic still works:
    echo "0000:00:03.0" > /sys/bus/pci/drivers/e1000/bind
    open firefox and try some web page.

when I use kvm without readonly memory slot, in step 2 it reports:
Rom Test: fail. this means we can write to the memory region of a rom,
which is quite not safe for the guest and host.

when I use kvm with readonly memory slot, in step 2 it reports:
    Rom Test: Okay.
and the error message prints out in host console:
    Guest is writing readonly memory, phys_addr: febc0000, len:4, data[0]:K,
    skip it
    Guest is writing readonly memory, phys_addr: febc0000, len:2, data[0]:V,
    skip it
this is what we write "KVMKVM".
this means write operation is not successful, and return back to qemu from kvm.
thus we can make the rom real rom.

Signed-off-by: Liu Sheng <liusheng@linux.vnet.ibm.com>
---
 kvm-all.c |   47 ++++++++++++++++++++++++++++++++++++-----------
 1 files changed, 36 insertions(+), 11 deletions(-)

diff --git a/kvm-all.c b/kvm-all.c
index badf1d8..1b66183 100644
--- a/kvm-all.c
+++ b/kvm-all.c
@@ -97,6 +97,9 @@ struct KVMState
     QTAILQ_HEAD(msi_hashtab, KVMMSIRoute) msi_hashtab[KVM_MSI_HASHTAB_SIZE];
     bool direct_msi;
 #endif
+#ifdef KVM_CAP_READONLY_MEM
+    int readonly_mem;
+#endif
 };
 
 KVMState *kvm_state;
@@ -261,9 +264,18 @@ err:
  * dirty pages logging control
  */
 
-static int kvm_mem_flags(KVMState *s, bool log_dirty)
+static int kvm_mem_flags(KVMState *s, MemoryRegion *mr)
 {
-    return log_dirty ? KVM_MEM_LOG_DIRTY_PAGES : 0;
+    int flags;
+    bool log_dirty = memory_region_is_logging(mr);
+    bool readonly = mr->readonly;
+    flags = log_dirty ? KVM_MEM_LOG_DIRTY_PAGES : 0;
+#ifdef KVM_CAP_READONLY_MEM
+    if (s->readonly_mem) {
+        flags |= readonly ? KVM_MEM_READONLY : 0;
+    }
+#endif
+    return flags;
 }
 
 static int kvm_slot_dirty_pages_log_change(KVMSlot *mem, bool log_dirty)
@@ -274,7 +286,7 @@ static int kvm_slot_dirty_pages_log_change(KVMSlot *mem, bool log_dirty)
 
     old_flags = mem->flags;
 
-    flags = (mem->flags & ~mask) | kvm_mem_flags(s, log_dirty);
+    flags = (mem->flags & ~mask) | (log_dirty ? mask : 0);
     mem->flags = flags;
 
     /* If nothing changed effectively, no need to issue ioctl */
@@ -622,7 +634,7 @@ static void kvm_set_phys_mem(MemoryRegionSection *section, bool add)
             mem->memory_size = old.memory_size;
             mem->start_addr = old.start_addr;
             mem->ram = old.ram;
-            mem->flags = kvm_mem_flags(s, log_dirty);
+            mem->flags = kvm_mem_flags(s, mr);
 
             err = kvm_set_user_memory_region(s, mem);
             if (err) {
@@ -643,7 +655,7 @@ static void kvm_set_phys_mem(MemoryRegionSection *section, bool add)
             mem->memory_size = start_addr - old.start_addr;
             mem->start_addr = old.start_addr;
             mem->ram = old.ram;
-            mem->flags =  kvm_mem_flags(s, log_dirty);
+            mem->flags =  kvm_mem_flags(s, mr);
 
             err = kvm_set_user_memory_region(s, mem);
             if (err) {
@@ -667,7 +679,7 @@ static void kvm_set_phys_mem(MemoryRegionSection *section, bool add)
             size_delta = mem->start_addr - old.start_addr;
             mem->memory_size = old.memory_size - size_delta;
             mem->ram = old.ram + size_delta;
-            mem->flags = kvm_mem_flags(s, log_dirty);
+            mem->flags = kvm_mem_flags(s, mr);
 
             err = kvm_set_user_memory_region(s, mem);
             if (err) {
@@ -689,7 +701,7 @@ static void kvm_set_phys_mem(MemoryRegionSection *section, bool add)
     mem->memory_size = size;
     mem->start_addr = start_addr;
     mem->ram = ram;
-    mem->flags = kvm_mem_flags(s, log_dirty);
+    mem->flags = kvm_mem_flags(s, mr);
 
     err = kvm_set_user_memory_region(s, mem);
     if (err) {
@@ -1393,6 +1405,10 @@ int kvm_init(void)
     s->direct_msi = (kvm_check_extension(s, KVM_CAP_SIGNAL_MSI) > 0);
 #endif
 
+#ifdef KVM_CAP_READONLY_MEM
+    s->readonly_mem = kvm_check_extension(s, KVM_CAP_READONLY_MEM);
+#endif
+
     s->intx_set_mask = kvm_check_extension(s, KVM_CAP_PCI_2_3);
 
     ret = kvm_arch_init(s);
@@ -1607,10 +1623,19 @@ int kvm_cpu_exec(CPUArchState *env)
             break;
         case KVM_EXIT_MMIO:
             DPRINTF("handle_mmio\n");
-            cpu_physical_memory_rw(run->mmio.phys_addr,
-                                   run->mmio.data,
-                                   run->mmio.len,
-                                   run->mmio.is_write);
+            if (run->mmio.write_readonly_mem) {
+                fprintf(stderr, "Guest is writing readonly memory, "
+                    "phys_addr: %llx, len:%x, data[0]:%c, skip it.\n",
+                    run->mmio.phys_addr,
+                    run->mmio.len,
+                    run->mmio.data[0]);
+            } else {
+                cpu_physical_memory_rw(run->mmio.phys_addr,
+                                       run->mmio.data,
+                                       run->mmio.len,
+                                       run->mmio.is_write);
+            }
+
             ret = 0;
             break;
         case KVM_EXIT_IRQ_WINDOW_OPEN:
-- 
1.7.7.6