Re: [RFC PATCH v2 2/3] KVM: selftests: add selftest driver for KVM to test memory slots for MMIO BARs

On Wed, Jan 03, 2024 at 04:44:57PM +0800, Yan Zhao wrote:

This driver is for testing KVM memory slots for device MMIO BARs that are mapped to pages serving as device resources.

This driver implements a mock device whose device resources are pages array that can be mmaped into user space. It provides ioctl interface to users to configure whether the pages are allocated as a compound huge page or not.

I just think that it can be used in other scenarios, not only KVM.

KVM selftest code can then map the mock device resource to KVM memslots to check if any error encountered. After VM shutdown, mock device resource's page reference counters are checked to ensure KVM does not hold extra reference count during memslot add/removal.

Signed-off-by: Yan Zhao yan.y.zhao@intel.com

lib/Kconfig.debug | 14 ++ lib/Makefile | 1 + lib/test_kvm_mock_device.c | 281 ++++++++++++++++++++++++++++++++ lib/test_kvm_mock_device_uapi.h | 16 ++ 4 files changed, 312 insertions(+) create mode 100644 lib/test_kvm_mock_device.c create mode 100644 lib/test_kvm_mock_device_uapi.h

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index cc7d53d9dc01..c0fd4b53db89 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -2922,6 +2922,20 @@ config TEST_HMM

 If unsure, say N.

+config TEST_KVM_MOCK_DEVICE

• tristate "Test page-backended BAR to KVM mock device"
• help

•  This is a mock KVM assigned device whose MMIO BAR is backended by
  

•  struct page.
  

•  Say M here if you want to build the "test_kvm_mock_device" module.
  

•  Doing so will allow you to run KVM selftest
  

•  tools/testing/selftest/kvm/set_memory_region_io, which tests
  

•  functionality of adding page-backended MMIO memslots in KVM and
  

•  ensures that reference count of the backend pages are correctly
  

•  handled.
  

•  If unsure, say N.
  

config TEST_FREE_PAGES tristate "Test freeing pages" help diff --git a/lib/Makefile b/lib/Makefile index 6b09731d8e61..894a185bbabd 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -83,6 +83,7 @@ obj-$(CONFIG_TEST_STATIC_KEYS) += test_static_key_base.o obj-$(CONFIG_TEST_DYNAMIC_DEBUG) += test_dynamic_debug.o obj-$(CONFIG_TEST_PRINTF) += test_printf.o obj-$(CONFIG_TEST_SCANF) += test_scanf.o +obj-$(CONFIG_TEST_KVM_MOCK_DEVICE) += test_kvm_mock_device.o

obj-$(CONFIG_TEST_BITMAP) += test_bitmap.o ifeq ($(CONFIG_CC_IS_CLANG)$(CONFIG_KASAN),yy) diff --git a/lib/test_kvm_mock_device.c b/lib/test_kvm_mock_device.c new file mode 100644 index 000000000000..4e7527c230cd --- /dev/null +++ b/lib/test_kvm_mock_device.c @@ -0,0 +1,281 @@ +// SPDX-License-Identifier: GPL-2.0 +/*

• • This is a module to test KVM DEVICE MMIO PASSTHROUGH.
• */

+#include <linux/init.h> +#include <linux/fs.h> +#include <linux/module.h> +#include <linux/kernel.h> +#include <linux/cdev.h> +#include <linux/device.h> +#include <linux/mm.h>

+#include "test_kvm_mock_device_uapi.h"

+/* kvm mock device */ +struct kvm_mock_dev {

• dev_t devt;
• struct device device;
• struct cdev cdev;

+}; +static struct kvm_mock_dev kvm_mock_dev;

+struct kvm_mock_device {

• bool compound;
• struct page *resource;
• u64 bar_size;
• int order;

Do you have plan to allow user to change the bar_size via IOCTL ? If no "order" and "bar_size" can be removed.

• int *ref_array;
• struct mutex lock;
• bool prepared;

+};

+static bool opened;

+#define BAR_SIZE 0x200000UL +#define DEFAULT_COMPOUND true

"kmdev->compound = true;" is more easy to understand, but "kmdev->compound = DEFAULT_COMPOUND;" not.

+static vm_fault_t kvm_mock_device_mmap_fault(struct vm_fault *vmf) +{

• struct vm_area_struct *vma = vmf->vma;
• struct kvm_mock_device *kmdev = vma->vm_private_data;
• struct page *p = kmdev->resource;
• vm_fault_t ret = VM_FAULT_NOPAGE;
• unsigned long addr;
• int i;
• for (addr = vma->vm_start, i = vma->vm_pgoff; addr < vma->vm_end;

•     addr += PAGE_SIZE, i++) {
  

Just question: Will it be enough if only map the accessed page for the testing purpose ?

• ret = vmf_insert_pfn(vma, addr, page_to_pfn(p + i));
  

• if (ret == VM_FAULT_NOPAGE)
  

• 	continue;
  

• zap_vma_ptes(vma, vma->vm_start, vma->vm_end - vma->vm_start);
  

• return ret;
  

• }
• return ret;

+}

+static const struct vm_operations_struct kvm_mock_device_mmap_ops = {

• .fault = kvm_mock_device_mmap_fault,

+};

+static int kvm_mock_device_fops_mmap(struct file *file, struct vm_area_struct *vma) +{

• struct kvm_mock_device *kmdev = file->private_data;
• u64 offset, req_len;
• int ret = 0;
• mutex_lock(&kmdev->lock);
• if (!kmdev->prepared) {

• ret = -ENODEV;
  

• goto out;
  

• }
• offset = vma->vm_pgoff << PAGE_SHIFT;
• req_len = vma->vm_end - vma->vm_start;
• if (offset + req_len > BAR_SIZE) {

• ret = -EINVAL;
  

• goto out;
  

• }
• vm_flags_set(vma, VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP);
• vma->vm_ops = &kvm_mock_device_mmap_ops;
• vma->vm_private_data = kmdev;

+out:

• mutex_unlock(&kmdev->lock);
• return ret;

+}

+static int kvm_mock_device_prepare_resource(struct kvm_mock_device *kmdev) +{

• gfp_t gfp_flags = GFP_KERNEL | __GFP_ZERO;
• unsigned int order = kmdev->order;
• unsigned long count = 1 << order;
• unsigned long i;
• struct page *p;
• int ret;
• mutex_lock(&kmdev->lock);
• if (kmdev->prepared) {

• ret = -EBUSY;
  

• goto out;
  

• }
• if (kmdev->compound)

• gfp_flags |= __GFP_COMP;
  

• p = alloc_pages_node(0, gfp_flags, order);

Please alloc_pages() to honor the memory policy of current task. Hardcode to node 0 just works, but not hard to do this better.

• if (!p) {

• ret = -ENOMEM;
  

• goto out;
  

• }
• kmdev->ref_array = kmalloc_array(count, sizeof(kmdev->ref_array),

• 			 GFP_KERNEL_ACCOUNT);
  

• if (!kmdev->ref_array) {

• __free_pages(p, order);
  

• ret = -ENOMEM;
  

• goto out;
  

• }
• for (i = 0; i < count; i++)

• kmdev->ref_array[i] = page_ref_count(p + i);
  

• kmdev->resource = p;
• kmdev->prepared = true;

+out:

• mutex_unlock(&kmdev->lock);
• return ret;

+}

+static int kvm_mock_device_check_resource_ref(struct kvm_mock_device *kmdev) +{

• u32 i, count = 1 << kmdev->order;
• struct page *p = kmdev->resource;
• int inequal = 0;
• mutex_lock(&kmdev->lock);
• if (!kmdev->prepared) {

• mutex_unlock(&kmdev->lock);
  

• return -ENODEV;
  

• }
• for (i = 0; i < count; i++) {

• if (kmdev->ref_array[i] == page_ref_count(p + i))
  

• 	continue;
  

• pr_err("kvm test device check resource page %d old ref=%d new ref=%d\n",
  

• 	i, kmdev->ref_array[i], page_ref_count(p + i));
  

How about just return a bitmap to userspace for each page ineuqal ? Or if inequal number itself is enough then just remove this output, in worst case it prints 512 times for 2MB bar case, which looks just useless.

• inequal++;
  

• }
• mutex_unlock(&kmdev->lock);
• return inequal;

+}

+static int kvm_mock_device_fops_open(struct inode *inode, struct file *filp) +{

• struct kvm_mock_device *kmdev;
• if (opened)

• return -EBUSY;
  

It can't work in case of 2 who open the device file at *real* same time, at least you need atomic helpers for that purpose.

BTW I saw "kvm_mock_devie" instance is per file level, so maybe not hard to remove this limitation ?

• kmdev = kzalloc(sizeof(*kmdev), GFP_KERNEL_ACCOUNT);
• if (!kmdev)

• return -ENOMEM;
  

• kmdev->compound = DEFAULT_COMPOUND;
• kmdev->bar_size = BAR_SIZE;
• kmdev->order = get_order(kmdev->bar_size);
• mutex_init(&kmdev->lock);
• filp->private_data = kmdev;
• opened = true;
• return 0;

+}

+static int kvm_mock_device_fops_release(struct inode *inode, struct file *filp) +{

• struct kvm_mock_device *kmdev = filp->private_data;
• if (kmdev->prepared)

• __free_pages(kmdev->resource, kmdev->order);
  

• mutex_destroy(&kmdev->lock);
• kfree(kmdev->ref_array);
• kfree(kmdev);
• opened = false;
• return 0;

+}

+static long kvm_mock_device_fops_unlocked_ioctl(struct file *filp,

• 			unsigned int command,
  

• 			unsigned long arg)
  

+{

• struct kvm_mock_device *kmdev = filp->private_data;
• int r;
• switch (command) {
• case KVM_MOCK_DEVICE_GET_BAR_SIZE: {

• u64 bar_size;
  

• bar_size = kmdev->bar_size;
  

• r = put_user(bar_size, (u64 __user *)arg);
  

• break;
  

• }
• case KVM_MOCK_DEVICE_PREPARE_RESOURCE: {

• u32 compound;
  

• r = get_user(compound, (u32 __user *)arg);
  

• if (r)
  

• 	return r;
  

• kmdev->compound = compound;
  

• r = kvm_mock_device_prepare_resource(kmdev);
  

• break;
  

• }
• case KVM_MOCK_DEVICE_CHECK_BACKEND_REF: {

• int inequal;
  

• inequal = kvm_mock_device_check_resource_ref(kmdev);
  

• if (inequal < 0)
  

• 	return inequal;
  

• r = put_user(inequal, (u32 __user *)arg);
  

• break;
  

• }
• default:

• r = -EOPNOTSUPP;
  

• }
• return r;

+}

+static const struct file_operations kvm_mock_device_fops = {

• .open = kvm_mock_device_fops_open,
• .release = kvm_mock_device_fops_release,
• .mmap = kvm_mock_device_fops_mmap,
• .unlocked_ioctl = kvm_mock_device_fops_unlocked_ioctl,
• .llseek = default_llseek,
• .owner = THIS_MODULE,

+};

+static int __init kvm_mock_device_test_init(void) +{

• int ret;
• ret = alloc_chrdev_region(&kvm_mock_dev.devt, 0, 1, "KVM-MOCK-DEVICE");

How about misc_register() ? Like how KVM create /dev/kvm. I think that will be more simpler.

• if (ret)

• goto out;
  

• cdev_init(&kvm_mock_dev.cdev, &kvm_mock_device_fops);
• kvm_mock_dev.cdev.owner = THIS_MODULE;
• device_initialize(&kvm_mock_dev.device);
• kvm_mock_dev.device.devt = MKDEV(MAJOR(kvm_mock_dev.devt), 0);
• ret = dev_set_name(&kvm_mock_dev.device, "kvm_mock_device");
• if (ret)

• goto out;
  

• ret = cdev_device_add(&kvm_mock_dev.cdev, &kvm_mock_dev.device);
• if (ret)

• goto out;
  

+out:

• return ret;

+}

+static void __exit kvm_mock_device_test_exit(void) +{

• cdev_device_del(&kvm_mock_dev.cdev, &kvm_mock_dev.device);
• unregister_chrdev_region(kvm_mock_dev.devt, 1);

+}

+module_init(kvm_mock_device_test_init); +module_exit(kvm_mock_device_test_exit); +MODULE_LICENSE("GPL"); diff --git a/lib/test_kvm_mock_device_uapi.h b/lib/test_kvm_mock_device_uapi.h new file mode 100644 index 000000000000..227d0bf1d430 --- /dev/null +++ b/lib/test_kvm_mock_device_uapi.h @@ -0,0 +1,16 @@ +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ +/*

• • This is a module to help test KVM guest access of KVM mock device's BAR,
• • whose backend is mapped to pages.
• */

+#ifndef _LIB_TEST_KVM_MOCK_DEVICE_UAPI_H +#define _LIB_TEST_KVM_MOCK_DEVICE_UAPI_H

+#include <linux/types.h> +#include <linux/ioctl.h>

+#define KVM_MOCK_DEVICE_GET_BAR_SIZE _IOR('M', 0x00, u64) +#define KVM_MOCK_DEVICE_PREPARE_RESOURCE _IOWR('M', 0x01, u32) +#define KVM_MOCK_DEVICE_CHECK_BACKEND_REF _IOWR('M', 0x02, u32)

+#endif /* _LIB_TEST_KVM_MOCK_DEVICE_UAPI_H */

2.17.1