[v13,23/24] virt: gunyah: Add ioeventfd

Message ID 20230509204801.2824351-24-quic_eberman@quicinc.com
State New
Headers
Series Drivers for Gunyah hypervisor |

Commit Message

Elliot Berman May 9, 2023, 8:48 p.m. UTC
  Allow userspace to attach an ioeventfd to an mmio address within the guest.

Co-developed-by: Prakruthi Deepak Heragu <quic_pheragu@quicinc.com>
Signed-off-by: Prakruthi Deepak Heragu <quic_pheragu@quicinc.com>
Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
---
 Documentation/virt/gunyah/vm-manager.rst |   2 +-
 drivers/virt/gunyah/Kconfig              |   9 ++
 drivers/virt/gunyah/Makefile             |   1 +
 drivers/virt/gunyah/gunyah_ioeventfd.c   | 130 +++++++++++++++++++++++
 include/uapi/linux/gunyah.h              |  37 +++++++
 5 files changed, 178 insertions(+), 1 deletion(-)
 create mode 100644 drivers/virt/gunyah/gunyah_ioeventfd.c
  

Comments

Alex Elder June 5, 2023, 7:50 p.m. UTC | #1
On 5/9/23 3:48 PM, Elliot Berman wrote:
> Allow userspace to attach an ioeventfd to an mmio address within the guest.
> 
> Co-developed-by: Prakruthi Deepak Heragu <quic_pheragu@quicinc.com>
> Signed-off-by: Prakruthi Deepak Heragu <quic_pheragu@quicinc.com>
> Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>

Looks good.  One question below.

Reviewed-by: Alex Elder <elder@linaro.org>

> ---
>   Documentation/virt/gunyah/vm-manager.rst |   2 +-
>   drivers/virt/gunyah/Kconfig              |   9 ++
>   drivers/virt/gunyah/Makefile             |   1 +
>   drivers/virt/gunyah/gunyah_ioeventfd.c   | 130 +++++++++++++++++++++++
>   include/uapi/linux/gunyah.h              |  37 +++++++
>   5 files changed, 178 insertions(+), 1 deletion(-)
>   create mode 100644 drivers/virt/gunyah/gunyah_ioeventfd.c
> 
> diff --git a/Documentation/virt/gunyah/vm-manager.rst b/Documentation/virt/gunyah/vm-manager.rst
> index c4960948c779..87838c5b5945 100644
> --- a/Documentation/virt/gunyah/vm-manager.rst
> +++ b/Documentation/virt/gunyah/vm-manager.rst
> @@ -115,7 +115,7 @@ the VM *before* the VM starts.
>   The argument types are documented below:
>   
>   .. kernel-doc:: include/uapi/linux/gunyah.h
> -   :identifiers: gh_fn_vcpu_arg gh_fn_irqfd_arg gh_irqfd_flags
> +   :identifiers: gh_fn_vcpu_arg gh_fn_irqfd_arg gh_irqfd_flags gh_fn_ioeventfd_arg gh_ioeventfd_flags
>   
>   Gunyah VCPU API Descriptions
>   ----------------------------
> diff --git a/drivers/virt/gunyah/Kconfig b/drivers/virt/gunyah/Kconfig
> index bc2c46d9df94..63bebc5b9f82 100644
> --- a/drivers/virt/gunyah/Kconfig
> +++ b/drivers/virt/gunyah/Kconfig
> @@ -48,3 +48,12 @@ config GUNYAH_IRQFD
>   	  on Gunyah virtual machine.
>   
>   	  Say Y/M here if unsure and you want to support Gunyah VMMs.
> +
> +config GUNYAH_IOEVENTFD
> +	tristate "Gunyah ioeventfd interface"
> +	depends on GUNYAH
> +	help
> +	  Enable kernel support for creating ioeventfds which can alert userspace
> +	  when a Gunyah virtual machine accesses a memory address.
> +
> +	  Say Y/M here if unsure and you want to support Gunyah VMMs.
> diff --git a/drivers/virt/gunyah/Makefile b/drivers/virt/gunyah/Makefile
> index ad212a1cf967..63ca11e74796 100644
> --- a/drivers/virt/gunyah/Makefile
> +++ b/drivers/virt/gunyah/Makefile
> @@ -8,3 +8,4 @@ obj-$(CONFIG_GUNYAH) += gunyah.o
>   
>   obj-$(CONFIG_GUNYAH_VCPU) += gunyah_vcpu.o
>   obj-$(CONFIG_GUNYAH_IRQFD) += gunyah_irqfd.o
> +obj-$(CONFIG_GUNYAH_IOEVENTFD) += gunyah_ioeventfd.o
> diff --git a/drivers/virt/gunyah/gunyah_ioeventfd.c b/drivers/virt/gunyah/gunyah_ioeventfd.c
> new file mode 100644
> index 000000000000..5b1b9fd9ac3a
> --- /dev/null
> +++ b/drivers/virt/gunyah/gunyah_ioeventfd.c
> @@ -0,0 +1,130 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) 2022-2023 Qualcomm Innovation Center, Inc. All rights reserved.
> + */
> +
> +#include <linux/eventfd.h>
> +#include <linux/file.h>
> +#include <linux/fs.h>
> +#include <linux/gunyah.h>
> +#include <linux/gunyah_vm_mgr.h>
> +#include <linux/module.h>
> +#include <linux/printk.h>
> +
> +#include <uapi/linux/gunyah.h>
> +
> +struct gh_ioeventfd {
> +	struct gh_vm_function_instance *f;
> +	struct gh_vm_io_handler io_handler;
> +
> +	struct eventfd_ctx *ctx;
> +};
> +
> +static int gh_write_ioeventfd(struct gh_vm_io_handler *io_dev, u64 addr, u32 len, u64 data)
> +{
> +	struct gh_ioeventfd *iofd = container_of(io_dev, struct gh_ioeventfd, io_handler);

Does a write of 0 bytes still signal an event?

> +
> +	eventfd_signal(iofd->ctx, 1);
> +	return 0;
> +}
> +
> +static struct gh_vm_io_handler_ops io_ops = {
> +	.write = gh_write_ioeventfd,
> +};
> +
> +static long gh_ioeventfd_bind(struct gh_vm_function_instance *f)
> +{
> +	const struct gh_fn_ioeventfd_arg *args = f->argp;
> +	struct gh_ioeventfd *iofd;
> +	struct eventfd_ctx *ctx;
> +	int ret;
> +
> +	if (f->arg_size != sizeof(*args))
> +		return -EINVAL;
> +
> +	/* All other flag bits are reserved for future use */
> +	if (args->flags & ~GH_IOEVENTFD_FLAGS_DATAMATCH)
> +		return -EINVAL;
> +
> +	/* must be natural-word sized, or 0 to ignore length */
> +	switch (args->len) {
> +	case 0:
> +	case 1:
> +	case 2:
> +	case 4:
> +	case 8:
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	/* check for range overflow */
> +	if (overflows_type(args->addr + args->len, u64))
> +		return -EINVAL;
> +
> +	/* ioeventfd with no length can't be combined with DATAMATCH */
> +	if (!args->len && (args->flags & GH_IOEVENTFD_FLAGS_DATAMATCH))
> +		return -EINVAL;
> +
> +	ctx = eventfd_ctx_fdget(args->fd);
> +	if (IS_ERR(ctx))
> +		return PTR_ERR(ctx);
> +
> +	iofd = kzalloc(sizeof(*iofd), GFP_KERNEL);
> +	if (!iofd) {
> +		ret = -ENOMEM;
> +		goto err_eventfd;
> +	}
> +
> +	f->data = iofd;
> +	iofd->f = f;
> +
> +	iofd->ctx = ctx;
> +
> +	if (args->flags & GH_IOEVENTFD_FLAGS_DATAMATCH) {
> +		iofd->io_handler.datamatch = true;
> +		iofd->io_handler.len = args->len;
> +		iofd->io_handler.data = args->datamatch;
> +	}
> +	iofd->io_handler.addr = args->addr;
> +	iofd->io_handler.ops = &io_ops;
> +
> +	ret = gh_vm_add_io_handler(f->ghvm, &iofd->io_handler);
> +	if (ret)
> +		goto err_io_dev_add;
> +
> +	return 0;
> +
> +err_io_dev_add:
> +	kfree(iofd);
> +err_eventfd:
> +	eventfd_ctx_put(ctx);
> +	return ret;
> +}
> +
> +static void gh_ioevent_unbind(struct gh_vm_function_instance *f)
> +{
> +	struct gh_ioeventfd *iofd = f->data;
> +
> +	eventfd_ctx_put(iofd->ctx);
> +	gh_vm_remove_io_handler(iofd->f->ghvm, &iofd->io_handler);
> +	kfree(iofd);
> +}
> +
> +static bool gh_ioevent_compare(const struct gh_vm_function_instance *f,
> +				const void *arg, size_t size)
> +{
> +	const struct gh_fn_ioeventfd_arg *instance = f->argp,
> +					 *other = arg;
> +
> +	if (sizeof(*other) != size)
> +		return false;
> +
> +	return instance->addr == other->addr;
> +}
> +
> +DECLARE_GH_VM_FUNCTION_INIT(ioeventfd, GH_FN_IOEVENTFD, 3,
> +				gh_ioeventfd_bind, gh_ioevent_unbind,
> +				gh_ioevent_compare);
> +MODULE_DESCRIPTION("Gunyah ioeventfd VM Function");
> +MODULE_LICENSE("GPL");
> diff --git a/include/uapi/linux/gunyah.h b/include/uapi/linux/gunyah.h
> index 0c480c622686..fa1cae7419d2 100644
> --- a/include/uapi/linux/gunyah.h
> +++ b/include/uapi/linux/gunyah.h
> @@ -79,10 +79,13 @@ struct gh_vm_dtb_config {
>    *              Return: file descriptor to manipulate the vcpu.
>    * @GH_FN_IRQFD: register eventfd to assert a Gunyah doorbell
>    *               &struct gh_fn_desc.arg is a pointer to &struct gh_fn_irqfd_arg
> + * @GH_FN_IOEVENTFD: register ioeventfd to trigger when VM faults on parameter
> + *                   &struct gh_fn_desc.arg is a pointer to &struct gh_fn_ioeventfd_arg
>    */
>   enum gh_fn_type {
>   	GH_FN_VCPU = 1,
>   	GH_FN_IRQFD,
> +	GH_FN_IOEVENTFD,
>   };
>   
>   #define GH_FN_MAX_ARG_SIZE		256
> @@ -134,6 +137,40 @@ struct gh_fn_irqfd_arg {
>   	__u32 padding;
>   };
>   
> +/**
> + * enum gh_ioeventfd_flags - flags for use in gh_fn_ioeventfd_arg
> + * @GH_IOEVENTFD_FLAGS_DATAMATCH: the event will be signaled only if the
> + *                                written value to the registered address is
> + *                                equal to &struct gh_fn_ioeventfd_arg.datamatch
> + */
> +enum gh_ioeventfd_flags {
> +	GH_IOEVENTFD_FLAGS_DATAMATCH	= 1UL << 0,
> +};
> +
> +/**
> + * struct gh_fn_ioeventfd_arg - Arguments to create an ioeventfd function
> + * @datamatch: data used when GH_IOEVENTFD_DATAMATCH is set
> + * @addr: Address in guest memory
> + * @len: Length of access
> + * @fd: When ioeventfd is matched, this eventfd is written
> + * @flags: See &enum gh_ioeventfd_flags
> + * @padding: padding bytes
> + *
> + * Create this function with &GH_VM_ADD_FUNCTION using type &GH_FN_IOEVENTFD.
> + *
> + * Attaches an ioeventfd to a legal mmio address within the guest. A guest write
> + * in the registered address will signal the provided event instead of triggering
> + * an exit on the GH_VCPU_RUN ioctl.
> + */
> +struct gh_fn_ioeventfd_arg {
> +	__u64 datamatch;
> +	__u64 addr;        /* legal mmio address */
> +	__u32 len;         /* 1, 2, 4, or 8 bytes; or 0 to ignore length */
> +	__s32 fd;
> +	__u32 flags;
> +	__u32 padding;
> +};
> +
>   /**
>    * struct gh_fn_desc - Arguments to create a VM function
>    * @type: Type of the function. See &enum gh_fn_type.
  
Elliot Berman June 9, 2023, 5:33 p.m. UTC | #2
On 6/5/2023 12:50 PM, Alex Elder wrote:
> On 5/9/23 3:48 PM, Elliot Berman wrote:
>> Allow userspace to attach an ioeventfd to an mmio address within the 
>> guest.
>>
>> Co-developed-by: Prakruthi Deepak Heragu <quic_pheragu@quicinc.com>
>> Signed-off-by: Prakruthi Deepak Heragu <quic_pheragu@quicinc.com>
>> Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
> 
> Looks good.  One question below.
> 
> Reviewed-by: Alex Elder <elder@linaro.org>
> 

Thanks!

>> ---
>>   Documentation/virt/gunyah/vm-manager.rst |   2 +-
>>   drivers/virt/gunyah/Kconfig              |   9 ++
>>   drivers/virt/gunyah/Makefile             |   1 +
>>   drivers/virt/gunyah/gunyah_ioeventfd.c   | 130 +++++++++++++++++++++++
>>   include/uapi/linux/gunyah.h              |  37 +++++++
>>   5 files changed, 178 insertions(+), 1 deletion(-)
>>   create mode 100644 drivers/virt/gunyah/gunyah_ioeventfd.c
>>
>> diff --git a/Documentation/virt/gunyah/vm-manager.rst 
>> b/Documentation/virt/gunyah/vm-manager.rst
>> index c4960948c779..87838c5b5945 100644
>> --- a/Documentation/virt/gunyah/vm-manager.rst
>> +++ b/Documentation/virt/gunyah/vm-manager.rst
>> @@ -115,7 +115,7 @@ the VM *before* the VM starts.
>>   The argument types are documented below:
>>   .. kernel-doc:: include/uapi/linux/gunyah.h
>> -   :identifiers: gh_fn_vcpu_arg gh_fn_irqfd_arg gh_irqfd_flags
>> +   :identifiers: gh_fn_vcpu_arg gh_fn_irqfd_arg gh_irqfd_flags 
>> gh_fn_ioeventfd_arg gh_ioeventfd_flags
>>   Gunyah VCPU API Descriptions
>>   ----------------------------
>> diff --git a/drivers/virt/gunyah/Kconfig b/drivers/virt/gunyah/Kconfig
>> index bc2c46d9df94..63bebc5b9f82 100644
>> --- a/drivers/virt/gunyah/Kconfig
>> +++ b/drivers/virt/gunyah/Kconfig
>> @@ -48,3 +48,12 @@ config GUNYAH_IRQFD
>>         on Gunyah virtual machine.
>>         Say Y/M here if unsure and you want to support Gunyah VMMs.
>> +
>> +config GUNYAH_IOEVENTFD
>> +    tristate "Gunyah ioeventfd interface"
>> +    depends on GUNYAH
>> +    help
>> +      Enable kernel support for creating ioeventfds which can alert 
>> userspace
>> +      when a Gunyah virtual machine accesses a memory address.
>> +
>> +      Say Y/M here if unsure and you want to support Gunyah VMMs.
>> diff --git a/drivers/virt/gunyah/Makefile b/drivers/virt/gunyah/Makefile
>> index ad212a1cf967..63ca11e74796 100644
>> --- a/drivers/virt/gunyah/Makefile
>> +++ b/drivers/virt/gunyah/Makefile
>> @@ -8,3 +8,4 @@ obj-$(CONFIG_GUNYAH) += gunyah.o
>>   obj-$(CONFIG_GUNYAH_VCPU) += gunyah_vcpu.o
>>   obj-$(CONFIG_GUNYAH_IRQFD) += gunyah_irqfd.o
>> +obj-$(CONFIG_GUNYAH_IOEVENTFD) += gunyah_ioeventfd.o
>> diff --git a/drivers/virt/gunyah/gunyah_ioeventfd.c 
>> b/drivers/virt/gunyah/gunyah_ioeventfd.c
>> new file mode 100644
>> index 000000000000..5b1b9fd9ac3a
>> --- /dev/null
>> +++ b/drivers/virt/gunyah/gunyah_ioeventfd.c
>> @@ -0,0 +1,130 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +/*
>> + * Copyright (c) 2022-2023 Qualcomm Innovation Center, Inc. All 
>> rights reserved.
>> + */
>> +
>> +#include <linux/eventfd.h>
>> +#include <linux/file.h>
>> +#include <linux/fs.h>
>> +#include <linux/gunyah.h>
>> +#include <linux/gunyah_vm_mgr.h>
>> +#include <linux/module.h>
>> +#include <linux/printk.h>
>> +
>> +#include <uapi/linux/gunyah.h>
>> +
>> +struct gh_ioeventfd {
>> +    struct gh_vm_function_instance *f;
>> +    struct gh_vm_io_handler io_handler;
>> +
>> +    struct eventfd_ctx *ctx;
>> +};
>> +
>> +static int gh_write_ioeventfd(struct gh_vm_io_handler *io_dev, u64 
>> addr, u32 len, u64 data)
>> +{
>> +    struct gh_ioeventfd *iofd = container_of(io_dev, struct 
>> gh_ioeventfd, io_handler);
> 
> Does a write of 0 bytes still signal an event?
> 

 From gunyah_ioeventfd perspective, yes. I don't think a write of 0 
bytes is possible, but maybe you are thinking of scenario I'm not?

>> +
>> +    eventfd_signal(iofd->ctx, 1);
>> +    return 0;
>> +}
>> +
>> +static struct gh_vm_io_handler_ops io_ops = {
>> +    .write = gh_write_ioeventfd,
>> +};
>> +
>> +static long gh_ioeventfd_bind(struct gh_vm_function_instance *f)
>> +{
>> +    const struct gh_fn_ioeventfd_arg *args = f->argp;
>> +    struct gh_ioeventfd *iofd;
>> +    struct eventfd_ctx *ctx;
>> +    int ret;
>> +
>> +    if (f->arg_size != sizeof(*args))
>> +        return -EINVAL;
>> +
>> +    /* All other flag bits are reserved for future use */
>> +    if (args->flags & ~GH_IOEVENTFD_FLAGS_DATAMATCH)
>> +        return -EINVAL;
>> +
>> +    /* must be natural-word sized, or 0 to ignore length */
>> +    switch (args->len) {
>> +    case 0:
>> +    case 1:
>> +    case 2:
>> +    case 4:
>> +    case 8:
>> +        break;
>> +    default:
>> +        return -EINVAL;
>> +    }
>> +
>> +    /* check for range overflow */
>> +    if (overflows_type(args->addr + args->len, u64))
>> +        return -EINVAL;
>> +
>> +    /* ioeventfd with no length can't be combined with DATAMATCH */
>> +    if (!args->len && (args->flags & GH_IOEVENTFD_FLAGS_DATAMATCH))
>> +        return -EINVAL;
>> +
>> +    ctx = eventfd_ctx_fdget(args->fd);
>> +    if (IS_ERR(ctx))
>> +        return PTR_ERR(ctx);
>> +
>> +    iofd = kzalloc(sizeof(*iofd), GFP_KERNEL);
>> +    if (!iofd) {
>> +        ret = -ENOMEM;
>> +        goto err_eventfd;
>> +    }
>> +
>> +    f->data = iofd;
>> +    iofd->f = f;
>> +
>> +    iofd->ctx = ctx;
>> +
>> +    if (args->flags & GH_IOEVENTFD_FLAGS_DATAMATCH) {
>> +        iofd->io_handler.datamatch = true;
>> +        iofd->io_handler.len = args->len;
>> +        iofd->io_handler.data = args->datamatch;
>> +    }
>> +    iofd->io_handler.addr = args->addr;
>> +    iofd->io_handler.ops = &io_ops;
>> +
>> +    ret = gh_vm_add_io_handler(f->ghvm, &iofd->io_handler);
>> +    if (ret)
>> +        goto err_io_dev_add;
>> +
>> +    return 0;
>> +
>> +err_io_dev_add:
>> +    kfree(iofd);
>> +err_eventfd:
>> +    eventfd_ctx_put(ctx);
>> +    return ret;
>> +}
>> +
>> +static void gh_ioevent_unbind(struct gh_vm_function_instance *f)
>> +{
>> +    struct gh_ioeventfd *iofd = f->data;
>> +
>> +    eventfd_ctx_put(iofd->ctx);
>> +    gh_vm_remove_io_handler(iofd->f->ghvm, &iofd->io_handler);
>> +    kfree(iofd);
>> +}
>> +
>> +static bool gh_ioevent_compare(const struct gh_vm_function_instance *f,
>> +                const void *arg, size_t size)
>> +{
>> +    const struct gh_fn_ioeventfd_arg *instance = f->argp,
>> +                     *other = arg;
>> +
>> +    if (sizeof(*other) != size)
>> +        return false;
>> +
>> +    return instance->addr == other->addr;
>> +}
>> +
>> +DECLARE_GH_VM_FUNCTION_INIT(ioeventfd, GH_FN_IOEVENTFD, 3,
>> +                gh_ioeventfd_bind, gh_ioevent_unbind,
>> +                gh_ioevent_compare);
>> +MODULE_DESCRIPTION("Gunyah ioeventfd VM Function");
>> +MODULE_LICENSE("GPL");
>> diff --git a/include/uapi/linux/gunyah.h b/include/uapi/linux/gunyah.h
>> index 0c480c622686..fa1cae7419d2 100644
>> --- a/include/uapi/linux/gunyah.h
>> +++ b/include/uapi/linux/gunyah.h
>> @@ -79,10 +79,13 @@ struct gh_vm_dtb_config {
>>    *              Return: file descriptor to manipulate the vcpu.
>>    * @GH_FN_IRQFD: register eventfd to assert a Gunyah doorbell
>>    *               &struct gh_fn_desc.arg is a pointer to &struct 
>> gh_fn_irqfd_arg
>> + * @GH_FN_IOEVENTFD: register ioeventfd to trigger when VM faults on 
>> parameter
>> + *                   &struct gh_fn_desc.arg is a pointer to &struct 
>> gh_fn_ioeventfd_arg
>>    */
>>   enum gh_fn_type {
>>       GH_FN_VCPU = 1,
>>       GH_FN_IRQFD,
>> +    GH_FN_IOEVENTFD,
>>   };
>>   #define GH_FN_MAX_ARG_SIZE        256
>> @@ -134,6 +137,40 @@ struct gh_fn_irqfd_arg {
>>       __u32 padding;
>>   };
>> +/**
>> + * enum gh_ioeventfd_flags - flags for use in gh_fn_ioeventfd_arg
>> + * @GH_IOEVENTFD_FLAGS_DATAMATCH: the event will be signaled only if the
>> + *                                written value to the registered 
>> address is
>> + *                                equal to &struct 
>> gh_fn_ioeventfd_arg.datamatch
>> + */
>> +enum gh_ioeventfd_flags {
>> +    GH_IOEVENTFD_FLAGS_DATAMATCH    = 1UL << 0,
>> +};
>> +
>> +/**
>> + * struct gh_fn_ioeventfd_arg - Arguments to create an ioeventfd 
>> function
>> + * @datamatch: data used when GH_IOEVENTFD_DATAMATCH is set
>> + * @addr: Address in guest memory
>> + * @len: Length of access
>> + * @fd: When ioeventfd is matched, this eventfd is written
>> + * @flags: See &enum gh_ioeventfd_flags
>> + * @padding: padding bytes
>> + *
>> + * Create this function with &GH_VM_ADD_FUNCTION using type 
>> &GH_FN_IOEVENTFD.
>> + *
>> + * Attaches an ioeventfd to a legal mmio address within the guest. A 
>> guest write
>> + * in the registered address will signal the provided event instead 
>> of triggering
>> + * an exit on the GH_VCPU_RUN ioctl.
>> + */
>> +struct gh_fn_ioeventfd_arg {
>> +    __u64 datamatch;
>> +    __u64 addr;        /* legal mmio address */
>> +    __u32 len;         /* 1, 2, 4, or 8 bytes; or 0 to ignore length */
>> +    __s32 fd;
>> +    __u32 flags;
>> +    __u32 padding;
>> +};
>> +
>>   /**
>>    * struct gh_fn_desc - Arguments to create a VM function
>>    * @type: Type of the function. See &enum gh_fn_type.
>
  
Alex Elder June 9, 2023, 5:46 p.m. UTC | #3
On 6/9/23 12:33 PM, Elliot Berman wrote:
>>> +static int gh_write_ioeventfd(struct gh_vm_io_handler *io_dev, u64 
>>> addr, u32 len, u64 data)
>>> +{
>>> +    struct gh_ioeventfd *iofd = container_of(io_dev, struct 
>>> gh_ioeventfd, io_handler);
>>
>> Does a write of 0 bytes still signal an event?
>>
> 
>  From gunyah_ioeventfd perspective, yes. I don't think a write of 0 
> bytes is possible, but maybe you are thinking of scenario I'm not?
> 
>>> +
>>> +    eventfd_signal(iofd->ctx, 1);
>>> +    return 0;
>>> +} 

No, I was just observing that eventfd_signal() is called regardless
of the value of len.

					-Alex
  

Patch

diff --git a/Documentation/virt/gunyah/vm-manager.rst b/Documentation/virt/gunyah/vm-manager.rst
index c4960948c779..87838c5b5945 100644
--- a/Documentation/virt/gunyah/vm-manager.rst
+++ b/Documentation/virt/gunyah/vm-manager.rst
@@ -115,7 +115,7 @@  the VM *before* the VM starts.
 The argument types are documented below:
 
 .. kernel-doc:: include/uapi/linux/gunyah.h
-   :identifiers: gh_fn_vcpu_arg gh_fn_irqfd_arg gh_irqfd_flags
+   :identifiers: gh_fn_vcpu_arg gh_fn_irqfd_arg gh_irqfd_flags gh_fn_ioeventfd_arg gh_ioeventfd_flags
 
 Gunyah VCPU API Descriptions
 ----------------------------
diff --git a/drivers/virt/gunyah/Kconfig b/drivers/virt/gunyah/Kconfig
index bc2c46d9df94..63bebc5b9f82 100644
--- a/drivers/virt/gunyah/Kconfig
+++ b/drivers/virt/gunyah/Kconfig
@@ -48,3 +48,12 @@  config GUNYAH_IRQFD
 	  on Gunyah virtual machine.
 
 	  Say Y/M here if unsure and you want to support Gunyah VMMs.
+
+config GUNYAH_IOEVENTFD
+	tristate "Gunyah ioeventfd interface"
+	depends on GUNYAH
+	help
+	  Enable kernel support for creating ioeventfds which can alert userspace
+	  when a Gunyah virtual machine accesses a memory address.
+
+	  Say Y/M here if unsure and you want to support Gunyah VMMs.
diff --git a/drivers/virt/gunyah/Makefile b/drivers/virt/gunyah/Makefile
index ad212a1cf967..63ca11e74796 100644
--- a/drivers/virt/gunyah/Makefile
+++ b/drivers/virt/gunyah/Makefile
@@ -8,3 +8,4 @@  obj-$(CONFIG_GUNYAH) += gunyah.o
 
 obj-$(CONFIG_GUNYAH_VCPU) += gunyah_vcpu.o
 obj-$(CONFIG_GUNYAH_IRQFD) += gunyah_irqfd.o
+obj-$(CONFIG_GUNYAH_IOEVENTFD) += gunyah_ioeventfd.o
diff --git a/drivers/virt/gunyah/gunyah_ioeventfd.c b/drivers/virt/gunyah/gunyah_ioeventfd.c
new file mode 100644
index 000000000000..5b1b9fd9ac3a
--- /dev/null
+++ b/drivers/virt/gunyah/gunyah_ioeventfd.c
@@ -0,0 +1,130 @@ 
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2022-2023 Qualcomm Innovation Center, Inc. All rights reserved.
+ */
+
+#include <linux/eventfd.h>
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/gunyah.h>
+#include <linux/gunyah_vm_mgr.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+
+#include <uapi/linux/gunyah.h>
+
+struct gh_ioeventfd {
+	struct gh_vm_function_instance *f;
+	struct gh_vm_io_handler io_handler;
+
+	struct eventfd_ctx *ctx;
+};
+
+static int gh_write_ioeventfd(struct gh_vm_io_handler *io_dev, u64 addr, u32 len, u64 data)
+{
+	struct gh_ioeventfd *iofd = container_of(io_dev, struct gh_ioeventfd, io_handler);
+
+	eventfd_signal(iofd->ctx, 1);
+	return 0;
+}
+
+static struct gh_vm_io_handler_ops io_ops = {
+	.write = gh_write_ioeventfd,
+};
+
+static long gh_ioeventfd_bind(struct gh_vm_function_instance *f)
+{
+	const struct gh_fn_ioeventfd_arg *args = f->argp;
+	struct gh_ioeventfd *iofd;
+	struct eventfd_ctx *ctx;
+	int ret;
+
+	if (f->arg_size != sizeof(*args))
+		return -EINVAL;
+
+	/* All other flag bits are reserved for future use */
+	if (args->flags & ~GH_IOEVENTFD_FLAGS_DATAMATCH)
+		return -EINVAL;
+
+	/* must be natural-word sized, or 0 to ignore length */
+	switch (args->len) {
+	case 0:
+	case 1:
+	case 2:
+	case 4:
+	case 8:
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	/* check for range overflow */
+	if (overflows_type(args->addr + args->len, u64))
+		return -EINVAL;
+
+	/* ioeventfd with no length can't be combined with DATAMATCH */
+	if (!args->len && (args->flags & GH_IOEVENTFD_FLAGS_DATAMATCH))
+		return -EINVAL;
+
+	ctx = eventfd_ctx_fdget(args->fd);
+	if (IS_ERR(ctx))
+		return PTR_ERR(ctx);
+
+	iofd = kzalloc(sizeof(*iofd), GFP_KERNEL);
+	if (!iofd) {
+		ret = -ENOMEM;
+		goto err_eventfd;
+	}
+
+	f->data = iofd;
+	iofd->f = f;
+
+	iofd->ctx = ctx;
+
+	if (args->flags & GH_IOEVENTFD_FLAGS_DATAMATCH) {
+		iofd->io_handler.datamatch = true;
+		iofd->io_handler.len = args->len;
+		iofd->io_handler.data = args->datamatch;
+	}
+	iofd->io_handler.addr = args->addr;
+	iofd->io_handler.ops = &io_ops;
+
+	ret = gh_vm_add_io_handler(f->ghvm, &iofd->io_handler);
+	if (ret)
+		goto err_io_dev_add;
+
+	return 0;
+
+err_io_dev_add:
+	kfree(iofd);
+err_eventfd:
+	eventfd_ctx_put(ctx);
+	return ret;
+}
+
+static void gh_ioevent_unbind(struct gh_vm_function_instance *f)
+{
+	struct gh_ioeventfd *iofd = f->data;
+
+	eventfd_ctx_put(iofd->ctx);
+	gh_vm_remove_io_handler(iofd->f->ghvm, &iofd->io_handler);
+	kfree(iofd);
+}
+
+static bool gh_ioevent_compare(const struct gh_vm_function_instance *f,
+				const void *arg, size_t size)
+{
+	const struct gh_fn_ioeventfd_arg *instance = f->argp,
+					 *other = arg;
+
+	if (sizeof(*other) != size)
+		return false;
+
+	return instance->addr == other->addr;
+}
+
+DECLARE_GH_VM_FUNCTION_INIT(ioeventfd, GH_FN_IOEVENTFD, 3,
+				gh_ioeventfd_bind, gh_ioevent_unbind,
+				gh_ioevent_compare);
+MODULE_DESCRIPTION("Gunyah ioeventfd VM Function");
+MODULE_LICENSE("GPL");
diff --git a/include/uapi/linux/gunyah.h b/include/uapi/linux/gunyah.h
index 0c480c622686..fa1cae7419d2 100644
--- a/include/uapi/linux/gunyah.h
+++ b/include/uapi/linux/gunyah.h
@@ -79,10 +79,13 @@  struct gh_vm_dtb_config {
  *              Return: file descriptor to manipulate the vcpu.
  * @GH_FN_IRQFD: register eventfd to assert a Gunyah doorbell
  *               &struct gh_fn_desc.arg is a pointer to &struct gh_fn_irqfd_arg
+ * @GH_FN_IOEVENTFD: register ioeventfd to trigger when VM faults on parameter
+ *                   &struct gh_fn_desc.arg is a pointer to &struct gh_fn_ioeventfd_arg
  */
 enum gh_fn_type {
 	GH_FN_VCPU = 1,
 	GH_FN_IRQFD,
+	GH_FN_IOEVENTFD,
 };
 
 #define GH_FN_MAX_ARG_SIZE		256
@@ -134,6 +137,40 @@  struct gh_fn_irqfd_arg {
 	__u32 padding;
 };
 
+/**
+ * enum gh_ioeventfd_flags - flags for use in gh_fn_ioeventfd_arg
+ * @GH_IOEVENTFD_FLAGS_DATAMATCH: the event will be signaled only if the
+ *                                written value to the registered address is
+ *                                equal to &struct gh_fn_ioeventfd_arg.datamatch
+ */
+enum gh_ioeventfd_flags {
+	GH_IOEVENTFD_FLAGS_DATAMATCH	= 1UL << 0,
+};
+
+/**
+ * struct gh_fn_ioeventfd_arg - Arguments to create an ioeventfd function
+ * @datamatch: data used when GH_IOEVENTFD_DATAMATCH is set
+ * @addr: Address in guest memory
+ * @len: Length of access
+ * @fd: When ioeventfd is matched, this eventfd is written
+ * @flags: See &enum gh_ioeventfd_flags
+ * @padding: padding bytes
+ *
+ * Create this function with &GH_VM_ADD_FUNCTION using type &GH_FN_IOEVENTFD.
+ *
+ * Attaches an ioeventfd to a legal mmio address within the guest. A guest write
+ * in the registered address will signal the provided event instead of triggering
+ * an exit on the GH_VCPU_RUN ioctl.
+ */
+struct gh_fn_ioeventfd_arg {
+	__u64 datamatch;
+	__u64 addr;        /* legal mmio address */
+	__u32 len;         /* 1, 2, 4, or 8 bytes; or 0 to ignore length */
+	__s32 fd;
+	__u32 flags;
+	__u32 padding;
+};
+
 /**
  * struct gh_fn_desc - Arguments to create a VM function
  * @type: Type of the function. See &enum gh_fn_type.