Re: [PATCH v4 06/14] virt: gunyah: Add sysfs nodes

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Wed, Sep 28, 2022 at 12:56:25PM -0700, Elliot Berman wrote:
> Add /sys/hypervisor support when detecting that Linux is running in a
> Gunyah environment. Export the version of Gunyah which is reported via
> the hyp_identify hypercall.
> 
> Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
> ---
>  .../ABI/testing/sysfs-hypervisor-gunyah       | 15 ++++
>  MAINTAINERS                                   |  1 +
>  drivers/virt/Makefile                         |  1 +
>  drivers/virt/gunyah/Makefile                  |  2 +
>  drivers/virt/gunyah/sysfs.c                   | 71 +++++++++++++++++++
>  5 files changed, 90 insertions(+)
>  create mode 100644 Documentation/ABI/testing/sysfs-hypervisor-gunyah
>  create mode 100644 drivers/virt/gunyah/Makefile
>  create mode 100644 drivers/virt/gunyah/sysfs.c
> 
> diff --git a/Documentation/ABI/testing/sysfs-hypervisor-gunyah b/Documentation/ABI/testing/sysfs-hypervisor-gunyah
> new file mode 100644
> index 000000000000..7d74e74e9edd
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-hypervisor-gunyah
> @@ -0,0 +1,15 @@
> +What:		/sys/hypervisor/gunyah/api
> +Date:		October 2022
> +KernelVersion:	6.1
> +Contact:	linux-arm-msm@vger.kernel.org
> +Description:	If running under Gunyah:
> +		The Gunyah API version.

What does this version mean?  What format is it in?

> +
> +What:		/sys/hypervisor/gunyah/variant
> +Date:		October 2022
> +KernelVersion:	6.1
> +Contact:	linux-arm-msm@vger.kernel.org
> +Description:	If running under Gunyah:
> +		Reports the build variant of Gunyah:
> +		The open source build of Gunyah will report "81".
> +		The Qualcomm build of Gunyah will report "72".

So there are only 2 versions variants?  What happens when you get a
third?  And why the odd numbers?

What will userspace do with this information and what tool will parse
it?

> diff --git a/MAINTAINERS b/MAINTAINERS
> index feafac12db35..a26e67ef36b4 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -8885,6 +8885,7 @@ M:	Elliot Berman <quic_eberman@quicinc.com>
>  M:	Murali Nalajala <quic_mnalajal@quicinc.com>
>  L:	linux-arm-msm@vger.kernel.org
>  S:	Supported
> +F:	Documentation/ABI/testing/sysfs-hypervisor-gunyah
>  F:	Documentation/devicetree/bindings/firmware/gunyah-hypervisor.yaml
>  F:	Documentation/virt/gunyah/
>  F:	arch/arm64/gunyah/
> diff --git a/drivers/virt/Makefile b/drivers/virt/Makefile
> index 093674e05c40..10b87f934730 100644
> --- a/drivers/virt/Makefile
> +++ b/drivers/virt/Makefile
> @@ -11,3 +11,4 @@ obj-$(CONFIG_NITRO_ENCLAVES)	+= nitro_enclaves/
>  obj-$(CONFIG_ACRN_HSM)		+= acrn/
>  obj-$(CONFIG_EFI_SECRET)	+= coco/efi_secret/
>  obj-$(CONFIG_SEV_GUEST)		+= coco/sev-guest/
> +obj-$(CONFIG_GUNYAH)		+= gunyah/
> diff --git a/drivers/virt/gunyah/Makefile b/drivers/virt/gunyah/Makefile
> new file mode 100644
> index 000000000000..e15f16c17142
> --- /dev/null
> +++ b/drivers/virt/gunyah/Makefile
> @@ -0,0 +1,2 @@
> +gunyah-y += sysfs.o
> +obj-$(CONFIG_GUNYAH) += gunyah.o
> diff --git a/drivers/virt/gunyah/sysfs.c b/drivers/virt/gunyah/sysfs.c
> new file mode 100644
> index 000000000000..ec11510cbece
> --- /dev/null
> +++ b/drivers/virt/gunyah/sysfs.c
> @@ -0,0 +1,71 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) 2022 Qualcomm Innovation Center, Inc. All rights reserved.
> + */
> +
> +#define pr_fmt(fmt) "gunyah: " fmt
> +
> +#include <linux/kobject.h>
> +#include <linux/module.h>
> +#include <linux/printk.h>
> +#include <linux/init.h>
> +#include <asm-generic/gunyah.h>
> +
> +static struct gh_hypercall_hyp_identify_resp gunyah_api;
> +
> +static ssize_t api_show(struct kobject *kobj, struct kobj_attribute *attr, char *buffer)
> +{
> +	return sysfs_emit(buffer, "%d\n", (int)GH_API_INFO_API_VERSION(gunyah_api.api_info));
> +}
> +static struct kobj_attribute api_attr = __ATTR_RO(api);
> +
> +static ssize_t variant_show(struct kobject *kobj, struct kobj_attribute *attr, char *buffer)
> +{
> +	return sysfs_emit(buffer, "%d\n", (int)GH_API_INFO_VARIANT(gunyah_api.api_info));
> +}
> +static struct kobj_attribute variant_attr = __ATTR_RO(variant);
> +
> +static struct attribute *gunyah_attrs[] = {
> +	&api_attr.attr,
> +	&variant_attr.attr,
> +	NULL
> +};
> +
> +static const struct attribute_group gunyah_group = {
> +	.name = "gunyah",
> +	.attrs = gunyah_attrs,
> +};
> +
> +static int __init gunyah_init(void)
> +{
> +	u32 uid[4];
> +
> +	gh_hypercall_get_uid(uid);

No error checking?

> +
> +	if (!(gh_uid_matches(GUNYAH, uid) || gh_uid_matches(QC_HYP, uid)))
> +		return 0;
> +
> +	gh_hypercall_hyp_identify(&gunyah_api);
> +
> +	if (GH_API_INFO_API_VERSION(gunyah_api.api_info) != 1) {
> +		pr_warn("Unrecognized gunyah version: %llu. Currently supported: 1\n",
> +			GH_API_INFO_API_VERSION(gunyah_api.api_info));

Shouldn't the "1" be defined somewhere?

> +		return 0;
> +	}
> +
> +	pr_notice("Running under Gunyah hypervisor %llx/v%lld\n",
> +		  GH_API_INFO_VARIANT(gunyah_api.api_info),
> +		  GH_API_INFO_API_VERSION(gunyah_api.api_info));

When kernel code is working properly, it is quiet.  What is this going
to be used for?

thanks,

greg k-h