Re: [RFC 1/2] KVM: add initial support for KVM_SET_IOREGION

[Jason Wang <jasowang@redhat.com>]

On 2021/1/4 上午4:32, Elena Afanasova wrote:
> On Thu, 2020-12-31 at 11:45 +0800, Jason Wang wrote:
>> On 2020/12/29 下午6:02, Elena Afanasova wrote:
>>> This vm ioctl adds or removes an ioregionfd MMIO/PIO region.
>> How about FAST_MMIO?
>>
> I’ll add KVM_IOREGION_FAST_MMIO flag support. So this may be suitable
> for triggers which could use posted writes. The struct ioregionfd_cmd
> size bits and the data field will be unused in this case.


Note that eventfd checks for length and have datamatch support. Do we 
need to do something similar.

I guess the idea is to have a generic interface to let eventfd work for 
ioregion as well.


>
>>> Guest
>>> read and write accesses are dispatched through the given ioregionfd
>>> instead of returning from ioctl(KVM_RUN). Regions can be deleted by
>>> setting fds to -1.
>>>
>>> Signed-off-by: Elena Afanasova <eafanasova@gmail.com>
>>> ---
>>>    arch/x86/kvm/Kconfig     |   1 +
>>>    arch/x86/kvm/Makefile    |   1 +
>>>    arch/x86/kvm/x86.c       |   1 +
>>>    include/linux/kvm_host.h |  17 +++
>>>    include/uapi/linux/kvm.h |  23 ++++
>>>    virt/kvm/Kconfig         |   3 +
>>>    virt/kvm/eventfd.c       |  25 +++++
>>>    virt/kvm/eventfd.h       |  14 +++
>>>    virt/kvm/ioregion.c      | 233
>>> +++++++++++++++++++++++++++++++++++++++
>>>    virt/kvm/ioregion.h      |  15 +++
>>>    virt/kvm/kvm_main.c      |  20 +++-
>>>    11 files changed, 350 insertions(+), 3 deletions(-)
>>>    create mode 100644 virt/kvm/eventfd.h
>>>    create mode 100644 virt/kvm/ioregion.c
>>>    create mode 100644 virt/kvm/ioregion.h
>>>
>>> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
>>> index f92dfd8ef10d..b914ef375199 100644
>>> --- a/arch/x86/kvm/Kconfig
>>> +++ b/arch/x86/kvm/Kconfig
>>> @@ -33,6 +33,7 @@ config KVM
>>>    	select HAVE_KVM_IRQ_BYPASS
>>>    	select HAVE_KVM_IRQ_ROUTING
>>>    	select HAVE_KVM_EVENTFD
>>> +	select KVM_IOREGION
>>>    	select KVM_ASYNC_PF
>>>    	select USER_RETURN_NOTIFIER
>>>    	select KVM_MMIO
>>> diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
>>> index b804444e16d4..b3b17dc9f7d4 100644
>>> --- a/arch/x86/kvm/Makefile
>>> +++ b/arch/x86/kvm/Makefile
>>> @@ -12,6 +12,7 @@ KVM := ../../../virt/kvm
>>>    kvm-y			+= $(KVM)/kvm_main.o
>>> $(KVM)/coalesced_mmio.o \
>>>    				$(KVM)/eventfd.o $(KVM)/irqchip.o
>>> $(KVM)/vfio.o
>>>    kvm-$(CONFIG_KVM_ASYNC_PF)	+= $(KVM)/async_pf.o
>>> +kvm-$(CONFIG_KVM_IOREGION)	+= $(KVM)/ioregion.o
>>>    
>>>    kvm-y			+= x86.o emulate.o i8259.o irq.o
>>> lapic.o \
>>>    			   i8254.o ioapic.o irq_comm.o cpuid.o pmu.o
>>> mtrr.o \
>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>>> index e545a8a613b1..ddb28f5ca252 100644
>>> --- a/arch/x86/kvm/x86.c
>>> +++ b/arch/x86/kvm/x86.c
>>> @@ -3739,6 +3739,7 @@ int kvm_vm_ioctl_check_extension(struct kvm
>>> *kvm, long ext)
>>>    	case KVM_CAP_X86_USER_SPACE_MSR:
>>>    	case KVM_CAP_X86_MSR_FILTER:
>>>    	case KVM_CAP_ENFORCE_PV_FEATURE_CPUID:
>>> +	case KVM_CAP_IOREGIONFD:
>>>    		r = 1;
>>>    		break;
>>>    	case KVM_CAP_SYNC_REGS:
>>> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
>>> index 7f2e2a09ebbd..7cd667dddba9 100644
>>> --- a/include/linux/kvm_host.h
>>> +++ b/include/linux/kvm_host.h
>>> @@ -470,6 +470,10 @@ struct kvm {
>>>    		struct mutex      resampler_lock;
>>>    	} irqfds;
>>>    	struct list_head ioeventfds;
>>> +#endif
>>> +#ifdef CONFIG_KVM_IOREGION
>>> +	struct list_head ioregions_mmio;
>>> +	struct list_head ioregions_pio;
>>>    #endif
>>>    	struct kvm_vm_stat stat;
>>>    	struct kvm_arch arch;
>>> @@ -1262,6 +1266,19 @@ static inline int kvm_ioeventfd(struct kvm
>>> *kvm, struct kvm_ioeventfd *args)
>>>    
>>>    #endif /* CONFIG_HAVE_KVM_EVENTFD */
>>>    
>>> +#ifdef CONFIG_KVM_IOREGION
>>> +void kvm_ioregionfd_init(struct kvm *kvm);
>>> +int kvm_ioregionfd(struct kvm *kvm, struct kvm_ioregion *args);
>>> +
>>> +#else
>>> +
>>> +static inline void kvm_ioregionfd_init(struct kvm *kvm) {}
>>> +static inline int kvm_ioregionfd(struct kvm *kvm, struct
>>> kvm_ioregion *args)
>>> +{
>>> +	return -ENOSYS;
>>> +}
>>> +#endif
>>> +
>>>    void kvm_arch_irq_routing_update(struct kvm *kvm);
>>>    
>>>    static inline void kvm_make_request(int req, struct kvm_vcpu
>>> *vcpu)
>>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>>> index ca41220b40b8..81e775778c66 100644
>>> --- a/include/uapi/linux/kvm.h
>>> +++ b/include/uapi/linux/kvm.h
>>> @@ -732,6 +732,27 @@ struct kvm_ioeventfd {
>>>    	__u8  pad[36];
>>>    };
>>>    
>>> +enum {
>>> +	kvm_ioregion_flag_nr_pio,
>>> +	kvm_ioregion_flag_nr_posted_writes,
>>> +	kvm_ioregion_flag_nr_max,
>>> +};
>>> +
>>> +#define KVM_IOREGION_PIO (1 << kvm_ioregion_flag_nr_pio)
>>> +#define KVM_IOREGION_POSTED_WRITES (1 <<
>>> kvm_ioregion_flag_nr_posted_writes)
>>> +
>>> +#define KVM_IOREGION_VALID_FLAG_MASK ((1 <<
>>> kvm_ioregion_flag_nr_max) - 1)
>>> +
>>> +struct kvm_ioregion {
>>> +	__u64 guest_paddr; /* guest physical address */
>>> +	__u64 memory_size; /* bytes */
>>> +	__u64 user_data;
>> What will this field do? Is it a token?
>>
> Yes, it’s an opaque token that can be used by userspace in order to
> determine which MemoryRegion to dispatch.


This part I don't understand. Userspace should know the fd number (which 
I guess should be sufficient?).


>
>>> +	__s32 rfd;
>>> +	__s32 wfd;
>>> +	__u32 flags;
>>> +	__u8  pad[28];
>>> +};
>> Is this possible to register the same fd with multiple GPA ranges?
>> If
>> not, do we need to check for fd collision?
>>
> Yes, it’s possible to register the same fd with multiple GPA ranges.
>
>>> +
>>>    #define KVM_X86_DISABLE_EXITS_MWAIT          (1 << 0)
>>>    #define KVM_X86_DISABLE_EXITS_HLT            (1 << 1)
>>>    #define KVM_X86_DISABLE_EXITS_PAUSE          (1 << 2)
>>> @@ -1053,6 +1074,7 @@ struct kvm_ppc_resize_hpt {
>>>    #define KVM_CAP_X86_USER_SPACE_MSR 188
>>>    #define KVM_CAP_X86_MSR_FILTER 189
>>>    #define KVM_CAP_ENFORCE_PV_FEATURE_CPUID 190
>>> +#define KVM_CAP_IOREGIONFD 191
>>>    
>>>    #ifdef KVM_CAP_IRQ_ROUTING
>>>    
>>> @@ -1308,6 +1330,7 @@ struct kvm_vfio_spapr_tce {
>>>    					struct
>>> kvm_userspace_memory_region)
>>>    #define KVM_SET_TSS_ADDR          _IO(KVMIO,   0x47)
>>>    #define KVM_SET_IDENTITY_MAP_ADDR _IOW(KVMIO,  0x48, __u64)
>>> +#define KVM_SET_IOREGION          _IOW(KVMIO,  0x49, struct
>>> kvm_ioregion)
>>>    
>>>    /* enable ucontrol for s390 */
>>>    struct kvm_s390_ucas_mapping {
>>> diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
>>> index 1c37ccd5d402..5e6620bbf000 100644
>>> --- a/virt/kvm/Kconfig
>>> +++ b/virt/kvm/Kconfig
>>> @@ -17,6 +17,9 @@ config HAVE_KVM_EVENTFD
>>>           bool
>>>           select EVENTFD
>>>    
>>> +config KVM_IOREGION
>>> +       bool
>>> +
>>>    config KVM_MMIO
>>>           bool
>>>    
>>> diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
>>> index c2323c27a28b..aadb73903f8b 100644
>>> --- a/virt/kvm/eventfd.c
>>> +++ b/virt/kvm/eventfd.c
>>> @@ -27,6 +27,7 @@
>>>    #include <trace/events/kvm.h>
>>>    
>>>    #include <kvm/iodev.h>
>>> +#include "ioregion.h"
>>>    
>>>    #ifdef CONFIG_HAVE_KVM_IRQFD
>>>    
>>> @@ -755,6 +756,23 @@ static const struct kvm_io_device_ops
>>> ioeventfd_ops = {
>>>    	.destructor = ioeventfd_destructor,
>>>    };
>>>    
>>> +#ifdef CONFIG_KVM_IOREGION
>>> +/* assumes kvm->slots_lock held */
>>> +bool kvm_eventfd_collides(struct kvm *kvm, int bus_idx,
>>> +			  u64 start, u64 size)
>>> +{
>>> +	struct _ioeventfd *_p;
>>> +
>>> +	list_for_each_entry(_p, &kvm->ioeventfds, list)
>>> +		if (_p->bus_idx == bus_idx &&
>>> +		    overlap(start, size, _p->addr,
>>> +			    !_p->length ? 8 : _p->length))
>>> +			return true;
>>> +
>>> +	return false;
>>> +}
>>> +#endif
>>> +
>>>    /* assumes kvm->slots_lock held */
>>>    static bool
>>>    ioeventfd_check_collision(struct kvm *kvm, struct _ioeventfd *p)
>>> @@ -770,6 +788,13 @@ ioeventfd_check_collision(struct kvm *kvm,
>>> struct _ioeventfd *p)
>>>    		       _p->datamatch == p->datamatch))))
>>>    			return true;
>>>    
>>> +#ifdef CONFIG_KVM_IOREGION
>>> +	if (p->bus_idx == KVM_MMIO_BUS || p->bus_idx == KVM_PIO_BUS)
>>> +		if (kvm_ioregion_collides(kvm, p->bus_idx, p->addr,
>>> +					  !p->length ? 8 : p->length))
>>> +			return true;
>>> +#endif
>>> +
>>>    	return false;
>>>    }
>>>    
>>> diff --git a/virt/kvm/eventfd.h b/virt/kvm/eventfd.h
>>> new file mode 100644
>>> index 000000000000..73a621eebae3
>>> --- /dev/null
>>> +++ b/virt/kvm/eventfd.h
>>> @@ -0,0 +1,14 @@
>>> +/* SPDX-License-Identifier: GPL-2.0-only */
>>> +#ifndef __KVM_EVENTFD_H__
>>> +#define __KVM_EVENTFD_H__
>>> +
>>> +#ifdef CONFIG_KVM_IOREGION
>>> +bool kvm_eventfd_collides(struct kvm *kvm, int bus_idx, u64 start,
>>> u64 size);
>>> +#else
>>> +static inline bool
>>> +kvm_eventfd_collides(struct kvm *kvm, int bus_idx, u64 start, u64
>>> size)
>>> +{
>>> +	return false;
>>> +}
>>> +#endif
>>> +#endif
>>> diff --git a/virt/kvm/ioregion.c b/virt/kvm/ioregion.c
>>> new file mode 100644
>>> index 000000000000..a200c3761343
>>> --- /dev/null
>>> +++ b/virt/kvm/ioregion.c
>>> @@ -0,0 +1,233 @@
>>> +// SPDX-License-Identifier: GPL-2.0-only
>>> +#include <linux/kvm_host.h>
>>> +#include <linux/fs.h>
>>> +#include <kvm/iodev.h>
>>> +#include "eventfd.h"
>>> +
>>> +void
>>> +kvm_ioregionfd_init(struct kvm *kvm)
>>> +{
>>> +	INIT_LIST_HEAD(&kvm->ioregions_mmio);
>>> +	INIT_LIST_HEAD(&kvm->ioregions_pio);
>>> +}
>>> +
>>> +struct ioregion {
>>> +	struct list_head     list;
>>> +	u64                  paddr;
>>> +	u64                  size;
>>> +	struct file         *rf;
>>> +	struct file         *wf;
>>> +	u64                  user_data;
>>> +	struct kvm_io_device dev;
>>> +	bool                 posted_writes;
>>> +};
>>> +
>>> +static inline struct ioregion *
>>> +to_ioregion(struct kvm_io_device *dev)
>>> +{
>>> +	return container_of(dev, struct ioregion, dev);
>>> +}
>>> +
>>> +/* assumes kvm->slots_lock held */
>>> +static void
>>> +ioregion_release(struct ioregion *p)
>>> +{
>>> +	fput(p->rf);
>>> +	fput(p->wf);
>>> +	list_del(&p->list);
>>> +	kfree(p);
>>> +}
>>> +
>>> +static int
>>> +ioregion_read(struct kvm_vcpu *vcpu, struct kvm_io_device *this,
>>> gpa_t addr,
>>> +	      int len, void *val)
>>> +{
>>> +	return 0;
>>> +}
>>> +
>>> +static int
>>> +ioregion_write(struct kvm_vcpu *vcpu, struct kvm_io_device *this,
>>> gpa_t addr,
>>> +		int len, const void *val)
>>> +{
>>> +	return 0;
>>> +}
>>> +
>>> +/*
>>> + * This function is called as KVM is completely shutting down.  We
>>> do not
>>> + * need to worry about locking just nuke anything we have as
>>> quickly as possible
>>> + */
>>> +static void
>>> +ioregion_destructor(struct kvm_io_device *this)
>>> +{
>>> +	struct ioregion *p = to_ioregion(this);
>>> +
>>> +	ioregion_release(p);
>>> +}
>>> +
>>> +static const struct kvm_io_device_ops ioregion_ops = {
>>> +	.read       = ioregion_read,
>>> +	.write      = ioregion_write,
>>> +	.destructor = ioregion_destructor,
>>> +};
>>> +
>>> +static inline struct list_head *
>>> +get_ioregion_list(struct kvm *kvm, enum kvm_bus bus_idx)
>>> +{
>>> +	return (bus_idx == KVM_MMIO_BUS) ?
>>> +		&kvm->ioregions_mmio : &kvm->ioregions_pio;
>>> +}
>>> +
>>> +/* check for not overlapping case and reverse */
>>> +inline bool
>>> +overlap(u64 start1, u64 size1, u64 start2, u64 size2)
>>> +{
>>> +	u64 end1 = start1 + size1 - 1;
>>> +	u64 end2 = start2 + size2 - 1;
>>> +
>>> +	return !(end1 < start2 || start1 >= end2);
>>> +}
>>> +
>>> +/* assumes kvm->slots_lock held */
>>> +bool
>>> +kvm_ioregion_collides(struct kvm *kvm, int bus_idx,
>>> +		      u64 start, u64 size)
>>> +{
>>> +	struct ioregion *_p;
>>> +	struct list_head *ioregions;
>>> +
>>> +	ioregions = get_ioregion_list(kvm, bus_idx);
>>> +	list_for_each_entry(_p, ioregions, list)
>>> +		if (overlap(start, size, _p->paddr, _p->size))
>>> +			return true;
>>> +
>>> +	return false;
>>> +}
>>> +
>>> +/* assumes kvm->slots_lock held */
>>> +static bool
>>> +ioregion_collision(struct kvm *kvm, struct ioregion *p, enum
>>> kvm_bus bus_idx)
>>> +{
>>> +	if (kvm_ioregion_collides(kvm, bus_idx, p->paddr, p->size) ||
>>> +	    kvm_eventfd_collides(kvm, bus_idx, p->paddr, p->size))
>>> +		return true;
>>> +
>>> +	return false;
>>> +}
>>> +
>>> +static enum kvm_bus
>>> +get_bus_from_flags(__u32 flags)
>>> +{
>>> +	if (flags & KVM_IOREGION_PIO)
>>> +		return KVM_PIO_BUS;
>>> +	return KVM_MMIO_BUS;
>>> +}
>>> +
>>> +int
>>> +kvm_set_ioregion(struct kvm *kvm, struct kvm_ioregion *args)
>>> +{
>>> +	struct ioregion *p;
>>> +	bool is_posted_writes;
>>> +	struct file *rfile, *wfile;
>>> +	enum kvm_bus bus_idx;
>>> +	int ret = 0;
>>> +
>>> +	if (!args->memory_size)
>>> +		return -EINVAL;
>>> +	if ((args->guest_paddr + args->memory_size - 1) < args-
>>>> guest_paddr)
>>> +		return -EINVAL;
>>> +	if (args->flags & ~KVM_IOREGION_VALID_FLAG_MASK)
>>> +		return -EINVAL;
>>> +
>>> +	rfile = fget(args->rfd);
>>> +	if (!rfile)
>>> +		return -EBADF;
>>> +	wfile = fget(args->wfd);
>>> +	if (!wfile) {
>>> +		fput(rfile);
>>> +		return -EBADF;
>>> +	}
>>> +	if ((rfile->f_flags & O_NONBLOCK) || (wfile->f_flags &
>>> O_NONBLOCK)) {
>>> +		ret = -EINVAL;
>>> +		goto fail;
>>> +	}
>> Instead of checking nonblocking, can we poll here?
>>
> Yes, it’s possible. It would be necessary in the case of out-of-order
> requests. But since multiple in-flight messages don’t seem to be a use
> case I’m not sure if it’s necessary. Typically device register accesses
> should not take a long time, so making them asynchronous doesn't seem
> like a practical advantage. Also this might complicate the code and
> make it slower. What do you think?


One issue I saw is that, if we register a single fd for e.g two regions. 
And those two regions were read in parallel from guest. It looks to me 
we don't have any synchronization in the current code.


>
>>> +	p = kzalloc(sizeof(*p), GFP_KERNEL_ACCOUNT);
>>> +	if (!p) {
>>> +		ret = -ENOMEM;
>>> +		goto fail;
>>> +	}
>>> +
>>> +	INIT_LIST_HEAD(&p->list);
>>> +	p->paddr = args->guest_paddr;
>>> +	p->size = args->memory_size;
>>> +	p->user_data = args->user_data;
>>> +	p->rf = rfile;
>>> +	p->wf = wfile;
>>> +	is_posted_writes = args->flags & KVM_IOREGION_POSTED_WRITES;
>>> +	p->posted_writes = is_posted_writes ? true : false;
>>> +	bus_idx = get_bus_from_flags(args->flags);
>>> +
>>> +	mutex_lock(&kvm->slots_lock);
>>> +
>>> +	if (ioregion_collision(kvm, p, bus_idx)) {
>>> +		ret = -EEXIST;
>>> +		goto unlock_fail;
>>> +	}
>>> +	kvm_iodevice_init(&p->dev, &ioregion_ops);
>>> +	ret = kvm_io_bus_register_dev(kvm, bus_idx, p->paddr, p->size,
>>> +				      &p->dev);
>>> +	if (ret < 0)
>>> +		goto unlock_fail;
>> We probably need to register to FAST_MMIO when bus_idx is MMIO.
>>
>>
>>> +	list_add_tail(&p->list, get_ioregion_list(kvm, bus_idx));
>>> +
>>> +	mutex_unlock(&kvm->slots_lock);
>>> +
>>> +	return 0;
>>> +
>>> +unlock_fail:
>>> +	mutex_unlock(&kvm->slots_lock);
>>> +	kfree(p);
>>> +fail:
>>> +	fput(rfile);
>>> +	fput(wfile);
>>> +
>>> +	return ret;
>>> +}
>>> +
>>> +static int
>>> +kvm_rm_ioregion(struct kvm *kvm, struct kvm_ioregion *args)
>>> +{
>>> +	struct ioregion         *p, *tmp;
>>> +	enum kvm_bus             bus_idx;
>>> +	int                      ret = -ENOENT;
>>> +	struct list_head        *ioregions;
>>> +
>>> +	if (args->rfd != -1 || args->wfd != -1)
>>> +		return -EINVAL;
>> If we want to use ioregion fd for doorbell, rfd is probably not
>> necessary here.
>>
> This condition is simply a requirement that region can be deleted in
> the case of both fds are set to -1.


Ok.

Thanks


>
>> Thanks
>>
>>
>>> +
>>> +	bus_idx = get_bus_from_flags(args->flags);
>>> +	ioregions = get_ioregion_list(kvm, bus_idx);
>>> +
>>> +	mutex_lock(&kvm->slots_lock);
>>> +
>>> +	list_for_each_entry_safe(p, tmp, ioregions, list) {
>>> +		if (p->paddr == args->guest_paddr  &&
>>> +		    p->size == args->memory_size) {
>>> +			kvm_io_bus_unregister_dev(kvm, bus_idx, &p-
>>>> dev);
>>> +			ioregion_release(p);
>>> +			ret = 0;
>>> +			break;
>>> +		}
>>> +	}
>>> +
>>> +	mutex_unlock(&kvm->slots_lock);
>>> +
>>> +	return ret;
>>> +}
>>> +
>>> +int
>>> +kvm_ioregionfd(struct kvm *kvm, struct kvm_ioregion *args)
>>> +{
>>> +	if (args->rfd == -1 || args->wfd == -1)
>>> +		return kvm_rm_ioregion(kvm, args);
>>> +	return kvm_set_ioregion(kvm, args);
>>> +}
>>> diff --git a/virt/kvm/ioregion.h b/virt/kvm/ioregion.h
>>> new file mode 100644
>>> index 000000000000..23ffa812ec7a
>>> --- /dev/null
>>> +++ b/virt/kvm/ioregion.h
>>> @@ -0,0 +1,15 @@
>>> +/* SPDX-License-Identifier: GPL-2.0-only */
>>> +#ifndef __KVM_IOREGION_H__
>>> +#define __KVM_IOREGION_H__
>>> +
>>> +#ifdef CONFIG_KVM_IOREGION
>>> +inline bool overlap(u64 start1, u64 size1, u64 start2, u64 size2);
>>> +bool kvm_ioregion_collides(struct kvm *kvm, int bus_idx, u64
>>> start, u64 size);
>>> +#else
>>> +static inline bool
>>> +kvm_ioregion_collides(struct kvm *kvm, int bus_idx, u64 start, u64
>>> size)
>>> +{
>>> +	return false;
>>> +}
>>> +#endif
>>> +#endif
>>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>>> index 2541a17ff1c4..385d8ec6350d 100644
>>> --- a/virt/kvm/kvm_main.c
>>> +++ b/virt/kvm/kvm_main.c
>>> @@ -747,6 +747,7 @@ static struct kvm *kvm_create_vm(unsigned long
>>> type)
>>>    	mmgrab(current->mm);
>>>    	kvm->mm = current->mm;
>>>    	kvm_eventfd_init(kvm);
>>> +	kvm_ioregionfd_init(kvm);
>>>    	mutex_init(&kvm->lock);
>>>    	mutex_init(&kvm->irq_lock);
>>>    	mutex_init(&kvm->slots_lock);
>>> @@ -3708,6 +3709,16 @@ static long kvm_vm_ioctl(struct file *filp,
>>>    		r = kvm_vm_ioctl_set_memory_region(kvm,
>>> &kvm_userspace_mem);
>>>    		break;
>>>    	}
>>> +	case KVM_SET_IOREGION: {
>>> +		struct kvm_ioregion data;
>>> +
>>> +		r = -EFAULT;
>>> +		if (copy_from_user(&data, argp, sizeof(data)))
>>> +			goto out;
>>> +
>>> +		r = kvm_ioregionfd(kvm, &data);
>>> +		break;
>>> +	}
>>>    	case KVM_GET_DIRTY_LOG: {
>>>    		struct kvm_dirty_log log;
>>>    
>>> @@ -4301,9 +4312,12 @@ int kvm_io_bus_register_dev(struct kvm *kvm,
>>> enum kvm_bus bus_idx, gpa_t addr,
>>>    	if (!bus)
>>>    		return -ENOMEM;
>>>    
>>> -	/* exclude ioeventfd which is limited by maximum fd */
>>> -	if (bus->dev_count - bus->ioeventfd_count > NR_IOBUS_DEVS - 1)
>>> -		return -ENOSPC;
>>> +	/* enforce hard limit if kmemcg is disabled and
>>> +	 * exclude ioeventfd which is limited by maximum fd
>>> +	 */
>>> +	if (!memcg_kmem_enabled())
>>> +		if (bus->dev_count - bus->ioeventfd_count >
>>> NR_IOBUS_DEVS - 1)
>>> +			return -ENOSPC;
>>>    
>>>    	new_bus = kmalloc(struct_size(bus, range, bus->dev_count + 1),
>>>    			  GFP_KERNEL_ACCOUNT);