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

[Elena Afanasova <eafanasova@gmail.com>]

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>
---
 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;
+	__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..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;
+	}
+	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;
+	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;
+
+	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);
-- 
2.25.1