linux-kernel - Re: [PATCH v2 1/3] drivers/s390/char: Add Ultravisor io device

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Date:   Wed, 2 Mar 2022 11:34:44 +0100
From:   Janosch Frank <frankja@...ux.ibm.com>
To:     Steffen Eiden <seiden@...ux.ibm.com>, linux-s390@...r.kernel.org
Cc:     Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 1/3] drivers/s390/char: Add Ultravisor io device

On 2/23/22 15:48, Steffen Eiden wrote:
> This patch adds a new miscdevice to expose some Ultravisor functions
> to userspace. Userspace can send IOCTLs to the uvdevice that will then
> emit a corresponding Ultravisor Call and hands the result over to
> userspace. The uvdevice is available if the Ultravisor Call facility is
> present.
> 
> Userspace is now able to call the Query Ultravisor Information
> Ultravisor Command through the uvdevice.
> 
> Signed-off-by: Steffen Eiden <seiden@...ux.ibm.com>
> ---
>   MAINTAINERS                           |   2 +
>   arch/s390/include/uapi/asm/uvdevice.h |  27 +++++
>   drivers/s390/char/Kconfig             |  11 ++
>   drivers/s390/char/Makefile            |   1 +
>   drivers/s390/char/uvdevice.c          | 145 ++++++++++++++++++++++++++
>   5 files changed, 186 insertions(+)
>   create mode 100644 arch/s390/include/uapi/asm/uvdevice.h
>   create mode 100644 drivers/s390/char/uvdevice.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 777cd6fa2b3d..f32e876f45c2 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -10577,9 +10577,11 @@ F:	Documentation/virt/kvm/s390*
>   F:	arch/s390/include/asm/gmap.h
>   F:	arch/s390/include/asm/kvm*
>   F:	arch/s390/include/uapi/asm/kvm*
> +F:	arch/s390/include/uapi/asm/uvdevice.h
>   F:	arch/s390/kernel/uv.c
>   F:	arch/s390/kvm/
>   F:	arch/s390/mm/gmap.c
> +F:	drivers/s390/char/uvdevice.c
>   F:	tools/testing/selftests/kvm/*/s390x/
>   F:	tools/testing/selftests/kvm/s390x/
>   
> diff --git a/arch/s390/include/uapi/asm/uvdevice.h b/arch/s390/include/uapi/asm/uvdevice.h
> new file mode 100644
> index 000000000000..60956f8d2dc0
> --- /dev/null
> +++ b/arch/s390/include/uapi/asm/uvdevice.h
> @@ -0,0 +1,27 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +/*
> + *  Copyright IBM Corp. 2022
> + *  Author(s): Steffen Eiden <seiden@...ux.ibm.com>
> + */
> +#ifndef __S390X_ASM_UVDEVICE_H
> +#define __S390X_ASM_UVDEVICE_H
> +
> +#include <linux/types.h>
> +
> +struct uvio_ioctl_cb {
> +	__u32 flags;
> +	__u16 uv_rc;			/* UV header rc value */
> +	__u16 uv_rrc;			/* UV header rrc value */
> +	__u64 argument_addr;		/* Userspace address of uvio argument */
> +	__u32 argument_len;
> +	__u8  reserved14[0x40 - 0x14];	/* must be zero */
> +};
> +
> +#define UVIO_QUI_MAX_LEN		0x8000
> +
> +#define UVIO_DEVICE_NAME "uv"
> +#define UVIO_TYPE_UVC 'u'
> +
> +#define UVIO_IOCTL_QUI _IOWR(UVIO_TYPE_UVC, 0x01, struct uvio_ioctl_cb)
> +
> +#endif  /* __S390X_ASM_UVDEVICE_H */
> diff --git a/drivers/s390/char/Kconfig b/drivers/s390/char/Kconfig
> index 6cc4b19acf85..2a828274257a 100644
> --- a/drivers/s390/char/Kconfig
> +++ b/drivers/s390/char/Kconfig
> @@ -184,3 +184,14 @@ config S390_VMUR
>   	depends on S390
>   	help
>   	  Character device driver for z/VM reader, puncher and printer.
> +
> +config S390_UV_UAPI
> +	def_tristate y
> +	prompt "Ultravisor userspace API"
> +	depends on PROTECTED_VIRTUALIZATION_GUEST

Please drop the dependency.
We want this to be available to both guest and host as QUI is available 
in both environments and more calls like this could follow.

We could put an option around the attestation but the savings are not 
worth the effort.