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

[Jason Wang <jasowang@redhat.com>]

On 2021/1/5 上午8:02, Elena Afanasova wrote:
> On Mon, 2021-01-04 at 13:34 +0800, Jason Wang wrote:
>> 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.
>>
> Do you think datamatch support is necessary for ioregionfd?


I'm not sure. But if we don't have this support, it probably means we 
can't use eventfd for ioregionfd.


>
>> I guess the idea is to have a generic interface to let eventfd work
>> for
>> ioregion as well.
>>
> It seems that posted writes is the only "fast" case in ioregionfd. So I
> was thinking about using FAST_MMIO for this case only. Maybe in some
> cases it will be better to just use ioeventfd. But I'm not sure.


To be a generic infrastructure, it's better to have this, but we can 
listen from the opinion of others.


>
>>>>> 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?).
>>
> I think the user_data field can be useful if same fd is registered with
> multiple GPA ranges.


Yes, but if I read the code correctly, we encode the address in the 
protocol. Isn't it 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.
>>
> Yes, you are right. That’s why there will be cmds/replies serialization
> in a v2 series.


I see.

Thanks


>
>>>>> +	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);