Re: [RESEND RFC v2 1/4] KVM: add initial support for KVM_SET_IOREGION

[Jason Wang <jasowang@redhat.com>]

On 2021/2/11 下午10:59, Stefan Hajnoczi wrote:
> On Wed, Feb 10, 2021 at 11:31:30AM -0800, Elena Afanasova wrote:
>> On Mon, 2021-02-08 at 14:21 +0800, Jason Wang wrote:
>>> On 2021/1/30 上午2:48, Elena Afanasova wrote:
>>>> This vm ioctl adds or removes an ioregionfd MMIO/PIO region. 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>
>>>> ---
>>>> Changes in v2:
>>>>     - changes after code review
>>>>
>>>>    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      | 232
>>>> +++++++++++++++++++++++++++++++++++++++
>>>>    virt/kvm/ioregion.h      |  15 +++
>>>>    virt/kvm/kvm_main.c      |  11 ++
>>>>    11 files changed, 343 insertions(+)
>>>>    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 */
>>> Do we really need __u64 here?
>>>
>>>
>>>> +	__u64 user_data;
>>>> +	__s32 rfd;
>>>> +	__s32 wfd;
>>>> +	__u32 flags;
>>>> +	__u8  pad[28];
>>>> +};
>>>> +
>>>>    #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..48ff92bca966
>>>> --- /dev/null
>>>> +++ b/virt/kvm/ioregion.c
>>>> @@ -0,0 +1,232 @@
>>>> +// 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;  /* guest physical address */
>>>> +	u64                  size;   /* size in bytes */
>>>> +	struct file         *rf;
>>>> +	struct file         *wf;
>>>> +	u64                  user_data; /* opaque token used by
>>>> userspace */
>>>> +	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 -EOPNOTSUPP;
>>>> +}
>>>> +
>>>> +static int
>>>> +ioregion_write(struct kvm_vcpu *vcpu, struct kvm_io_device *this,
>>>> gpa_t addr,
>>>> +		int len, const void *val)
>>>> +{
>>>> +	return -EOPNOTSUPP;
>>>> +}
>>>> +
>>>> +/*
>>>> + * 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;
>>>> +	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;
>>>> +
>>>> +	rfile = fget(args->rfd);
>>>> +	if (!rfile)
>>>> +		return -EBADF;
>>> So the question still, if we want to use ioregion fd for doorbell,
>>> we
>>> don't need rfd in this case?
>>>
>> Using ioregionfd for doorbell seems to be an open question. Probably it
>> could just focus on the non-doorbell cases.
> Below you replied FAST_MMIO will be in v3. That is the doorbell case, so
> maybe it is in scope for this patch series?
>
> I think continuing to use ioeventfd for most doorbell registers makes
> sense.
>
> However, there are two cases where ioregionfd doorbell support is
> interesting:
>
> 1. The (non-FAST_MMIO) case where the application needs to know the
>     value written to the doorbell. ioeventfd cannot do this (datamatch
>     can handle a subset of cases but not all) so we need ioregionfd for
>     this.
>
> 2. The FAST_MMIO case just for convenience if applications prefer to use
>     a single API (ioregionfd) instead of implementing both ioregionfd and
>     ioeventfd.


Yes.


>
> ioeventfd will still have its benefits (and limitations) that make it
> different from ioregionfd. In particular, ioregionfd will not merge
> doorbell writes into a single message because doing so would basically
> involve reimplementing ioeventfd functionality as part of ioregionfd and
> isn't compatible with the current approach where userspace can provide
> any file descriptor for communication.
>
> Elena and Jason: do you agree with this API design?


I agree.

Thanks