Re: [PATCH v13 23/24] virt: gunyah: Add ioeventfd

[Alex Elder <elder@linaro.org>]

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.