Re: [PATCH v13 03/24] virt: gunyah: Add hypercalls to identify Gunyah

[Alex Elder <elder@linaro.org>]

On 5/9/23 3:47 PM, Elliot Berman wrote:
> Add hypercalls to identify when Linux is running a virtual machine under
> Gunyah.
> 
> There are two calls to help identify Gunyah:
> 
> 1. gh_hypercall_get_uid() returns a UID when running under a Gunyah
>     hypervisor.
> 2. gh_hypercall_hyp_identify() returns build information and a set of
>     feature flags that are supported by Gunyah.
> 
> Reviewed-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
> Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>

I have a suggestion below.  But whether or not you choose to
incorporate it:

Reviewed-by: Alex Elder <elder@linaro.org>

> ---
>   arch/arm64/Kbuild                    |  1 +
>   arch/arm64/gunyah/Makefile           |  3 ++
>   arch/arm64/gunyah/gunyah_hypercall.c | 56 ++++++++++++++++++++++++++++
>   drivers/virt/Kconfig                 |  2 +
>   drivers/virt/gunyah/Kconfig          | 13 +++++++
>   include/linux/gunyah.h               | 31 +++++++++++++++
>   6 files changed, 106 insertions(+)
>   create mode 100644 arch/arm64/gunyah/Makefile
>   create mode 100644 arch/arm64/gunyah/gunyah_hypercall.c
>   create mode 100644 drivers/virt/gunyah/Kconfig
> 
> diff --git a/arch/arm64/Kbuild b/arch/arm64/Kbuild
> index 5bfbf7d79c99..e4847ba0e3c9 100644
> --- a/arch/arm64/Kbuild
> +++ b/arch/arm64/Kbuild
> @@ -3,6 +3,7 @@ obj-y			+= kernel/ mm/ net/
>   obj-$(CONFIG_KVM)	+= kvm/
>   obj-$(CONFIG_XEN)	+= xen/
>   obj-$(subst m,y,$(CONFIG_HYPERV))	+= hyperv/
> +obj-$(CONFIG_GUNYAH)	+= gunyah/
>   obj-$(CONFIG_CRYPTO)	+= crypto/
>   
>   # for cleaning
> diff --git a/arch/arm64/gunyah/Makefile b/arch/arm64/gunyah/Makefile
> new file mode 100644
> index 000000000000..84f1e38cafb1
> --- /dev/null
> +++ b/arch/arm64/gunyah/Makefile
> @@ -0,0 +1,3 @@
> +# SPDX-License-Identifier: GPL-2.0
> +
> +obj-$(CONFIG_GUNYAH) += gunyah_hypercall.o
> diff --git a/arch/arm64/gunyah/gunyah_hypercall.c b/arch/arm64/gunyah/gunyah_hypercall.c
> new file mode 100644
> index 000000000000..2166d5dab869
> --- /dev/null
> +++ b/arch/arm64/gunyah/gunyah_hypercall.c
> @@ -0,0 +1,56 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) 2022-2023 Qualcomm Innovation Center, Inc. All rights reserved.
> + */
> +
> +#include <linux/arm-smccc.h>
> +#include <linux/module.h>
> +#include <linux/gunyah.h>
> +#include <linux/uuid.h>
> +
> +/* {c1d58fcd-a453-5fdb-9265-ce36673d5f14} */
> +static const uuid_t GUNYAH_UUID =
> +	UUID_INIT(0xc1d58fcd, 0xa453, 0x5fdb, 0x92, 0x65, 0xce, 0x36, 0x67, 0x3d, 0x5f, 0x14);
> +
> +bool arch_is_gh_guest(void)
> +{
> +	struct arm_smccc_res res;
> +	uuid_t uuid;
> +
> +	arm_smccc_1_1_hvc(ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID, &res);
> +
> +	((u32 *)&uuid.b[0])[0] = lower_32_bits(res.a0);
> +	((u32 *)&uuid.b[0])[1] = lower_32_bits(res.a1);
> +	((u32 *)&uuid.b[0])[2] = lower_32_bits(res.a2);
> +	((u32 *)&uuid.b[0])[3] = lower_32_bits(res.a3);

I think I'd rather see this more like:

	u32	*up = (u32 *)&uuid.b;

	/* The lower bytes of the four result fields encode the UUID */
	*up++ = lower_32_bits(res.a0);
	*up++ = lower_32_bits(res.a1);
	*up++ = lower_32_bits(res.a2);
	*up = lower_32_bits(res.a3);

Basically I think casting the assigned-to value makes things
harder to read.  So doing that cast just once seems simpler.
But it's not a big deal.

> +
> +	return uuid_equal(&uuid, &GUNYAH_UUID);
> +}
> +EXPORT_SYMBOL_GPL(arch_is_gh_guest);

. . .