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SubjectRe: [PATCH v3 2/8] platform/x86: dell-smbios: Introduce a WMI-ACPI interface
On Wed, Sep 27, 2017 at 11:02:14PM -0500, Mario Limonciello wrote:
> The driver currently uses an SMI interface which grants direct access
> to physical memory to the firmware SMM methods via a pointer.
>
> Now add a WMI-ACPI interface that is detected by WMI probe and preferred
> over the SMI interface.
>
> Changing this to operate over WMI-ACPI will use an ACPI OperationRegion
> for a buffer of data storage when SMM calls are performed.
>
> This is a safer approach to use in kernel drivers as the SMM will
> only have access to that OperationRegion.
>
> As a result, this change removes the dependency on this driver on the
> dcdbas kernel module. It's now an optional compilation option.
>
> When modifying this, add myself to MAINTAINERS.
>
> Signed-off-by: Mario Limonciello <mario.limonciello@dell.com>
> ---

...

> +DELL SMBIOS DRIVER
> +M: Pali Rohár <pali.rohar@gmail.com>
> +M: Mario Limonciello <mario.limonciello@dell.com>
> +S: Maintained
> +F: drivers/platform/x86/dell-smbios.*

Pali, do you agree with this?

...

> int dell_smbios_error(int value)
> @@ -60,13 +69,15 @@ struct calling_interface_buffer *dell_smbios_get_buffer(void)
> {
> mutex_lock(&buffer_mutex);
> dell_smbios_clear_buffer();
> + if (wmi_dev)
> + return &((struct wmi_calling_interface_buffer *) buffer)->smi;
> return buffer;

Hrm, my hope had been to make this transparent at this level. ... This
may need more thought. I don't care for the casting here.... hopefully
enlightenment lies below...

> +static int run_wmi_smbios_call(struct wmi_calling_interface_buffer *buf)
> +{
> + struct acpi_buffer output = {ACPI_ALLOCATE_BUFFER, NULL};
> + struct acpi_buffer input;
> + union acpi_object *obj;
> + acpi_status status;
> +
> + input.length = sizeof(struct wmi_calling_interface_buffer);
> + input.pointer = buf;
> +
> + status = wmidev_evaluate_method(wmi_dev, 0, 1, &input, &output);
> + if (ACPI_FAILURE(status)) {
> + pr_err("%x/%x [%x,%x,%x,%x] call failed\n",
> + buf->smi.class, buf->smi.select,
> + buf->smi.input[0], buf->smi.input[1],
> + buf->smi.input[2], buf->smi.input[3]);
> + return -EIO;
> + }
> + obj = (union acpi_object *)output.pointer;
> + if (obj->type != ACPI_TYPE_BUFFER) {
> + pr_err("invalid type : %d\n", obj->type);
> + return -EIO;
> + }

We ensure we don't write beyond buf, but we havne't ensured we don't read beyond
obj.


if (obj->length != input.length) { // or maybe >= ??
pr_err("invalid buffer length : %d\n", obj->length);
return -EINVAL;
}

> -static int __init dell_smbios_init(void)
> +static int dell_smbios_wmi_probe(struct wmi_device *wdev)
> +{
> + /* no longer need the SMI page */
> + free_page((unsigned long)buffer);
> +
> + /* WMI buffer should be 32k */
> + buffer = (void *)__get_free_pages(GFP_KERNEL, 3);

Assuming PAGE_SIZE here (I know, this driver, this architecture,
etc...). But, please use get_order() to determine number of pages
from a linear size:

__get_free_pages(GFP_KERNEL, get_order(32768));

> + if (!buffer)
> + return -ENOMEM;
> + bufferlen = sizeof(struct wmi_calling_interface_buffer);

Use a consistent way to allocate and set the len. Maybe set bufferlen
above and use get_order(bufferlen).

> + wmi_dev = wdev;
> + return 0;
> +}
> +
> +static int dell_smbios_wmi_remove(struct wmi_device *wdev)
> {
> - int ret;
> + wmi_dev = NULL;
> + free_pages((unsigned long)buffer, 3);
> + return 0;
> +}
>
> +static const struct wmi_device_id dell_smbios_wmi_id_table[] = {
> + { .guid_string = DELL_WMI_SMBIOS_GUID },
> + { },
> +};
> +
> +static struct wmi_driver dell_wmi_smbios_driver = {
> + .driver = {
> + .name = "dell-smbios",
> + },
> + .probe = dell_smbios_wmi_probe,
> + .remove = dell_smbios_wmi_remove,
> + .id_table = dell_smbios_wmi_id_table,
> +};
> +
> +static int __init dell_smbios_init(void)
> +{
> dmi_walk(find_tokens, NULL);
>
> if (!da_tokens) {
> @@ -181,34 +270,39 @@ static int __init dell_smbios_init(void)
> return -ENODEV;
> }
>
> +#ifdef CONFIG_DCDBAS

If this cannot be avoided, then use IS_ENABLED(CONFIG_DCDBAS).

I still think we should be to come up with a cleaner way to deal with
the two buffers than a bunch of #ifdefs and if (wdev) {} else {} blocks.

...
> diff --git a/drivers/platform/x86/dell-smbios.h b/drivers/platform/x86/dell-smbios.h
...
> -/* This structure will be modified by the firmware when we enter
> - * system management mode, hence the volatiles */
> -
> +/* If called through fallback SMI rather than WMI this structure will be
> + * modified by the firmware when we enter system management mode, hence the
> + * volatiles
> + */

Follow coding style when modifying comment blocks (even when they
didn't before) please. See coding-style 8) COmmenting.

/*
* If called ...
...
* volatiles.
*/

--
Darren Hart
VMware Open Source Technology Center

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