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

[Elliot Berman <quic_eberman@quicinc.com>]

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.
>