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Date:   Thu, 3 Aug 2023 00:48:57 +0000
From:   Wei Liu <wei.liu@kernel.org>
To:     Nuno Das Neves <nunodasneves@linux.microsoft.com>
Cc:     linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org,
        x86@kernel.org, linux-arm-kernel@lists.infradead.org,
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        hpa@zytor.com, will@kernel.org, catalin.marinas@arm.com
Subject: Re: [PATCH 14/15] asm-generic: hyperv: Use mshv headers
 conditionally. Add asm-generic/hyperv-defs.h
Message-ID: <ZMr5ebxAqfjHPkVb@liuwe-devbox-debian-v2>
References: <1690487690-2428-1-git-send-email-nunodasneves@linux.microsoft.com>
 <1690487690-2428-15-git-send-email-nunodasneves@linux.microsoft.com>
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On Thu, Jul 27, 2023 at 12:54:49PM -0700, Nuno Das Neves wrote:
> In order to keep unstable hyper-v interfaces independent of
> hyperv-tlfs.h, hvhdk.h must replace hyperv-tlfs.h eveywhere it will be
> used in the mshv driver.

Please properly capitalize "Hyper-V" when it is used as a term.

> Add hyperv-defs.h to replace some inclusions of hyperv-tlfs.h.
> It includes hyperv-tlfs.h or hvhdk.h depending on a compile-time constant
> HV_HYPERV_DEFS which will be defined in the mshv driver.
> 
> Signed-off-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
> ---
>  arch/arm64/include/asm/mshyperv.h |  2 +-
>  arch/x86/include/asm/mshyperv.h   |  3 +--
>  drivers/hv/hyperv_vmbus.h         |  1 -
>  include/asm-generic/hyperv-defs.h | 26 ++++++++++++++++++++++++++
>  include/asm-generic/mshyperv.h    |  2 +-
>  include/linux/hyperv.h            |  2 +-
>  6 files changed, 30 insertions(+), 6 deletions(-)
>  create mode 100644 include/asm-generic/hyperv-defs.h
> 
[...]
> diff --git a/include/asm-generic/hyperv-defs.h b/include/asm-generic/hyperv-defs.h
> new file mode 100644
> index 000000000000..ac6fcba35c8c
> --- /dev/null
> +++ b/include/asm-generic/hyperv-defs.h
> @@ -0,0 +1,26 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ASM_GENERIC_HYPERV_DEFS_H
> +#define _ASM_GENERIC_HYPERV_DEFS_H
> +
> +/*
> + * There are cases where Microsoft Hypervisor ABIs are needed which may not be
> + * stable or present in the Hyper-V TLFS document. E.g. the mshv_root driver.
> + *
> + * As these interfaces are unstable and may differ from hyperv-tlfs.h, they
> + * must be kept separate and independent.
> + *
> + * However, code from files that depend on hyperv-tlfs.h (such as mshyperv.h)
> + * is still needed, so work around the issue by conditionally including the
> + * correct definitions.
> + *
> + * Note: Since they are independent of each other, there are many definitions
> + * duplicated in both hyperv-tlfs.h and uapi/hyperv/hv*.h files.
> + */

Is this because we accidentally introduced some host only, unstable
interfaces to hyperv-tlfs.h? Is the long term plan to drop those from
hyperv-tlfs.h and further separate the helper functions?

Thanks,
Wei.

> +#ifdef HV_HYPERV_DEFS
> +#include <uapi/hyperv/hvhdk.h>
> +#else
> +#include <asm/hyperv-tlfs.h>
> +#endif
> +
> +#endif /* _ASM_GENERIC_HYPERV_DEFS_H */
> +
> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
> index 2b20994d809e..e86b6f51fb64 100644
> --- a/include/asm-generic/mshyperv.h
> +++ b/include/asm-generic/mshyperv.h
> @@ -25,7 +25,7 @@
>  #include <linux/cpumask.h>
>  #include <linux/nmi.h>
>  #include <asm/ptrace.h>
> -#include <asm/hyperv-tlfs.h>
> +#include <asm-generic/hyperv-defs.h>
>  
>  #define VTPM_BASE_ADDRESS 0xfed40000
>  
> diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
> index f90de5abcd50..66ed8b3e5d89 100644
> --- a/include/linux/hyperv.h
> +++ b/include/linux/hyperv.h
> @@ -24,7 +24,7 @@
>  #include <linux/mod_devicetable.h>
>  #include <linux/interrupt.h>
>  #include <linux/reciprocal_div.h>
> -#include <asm/hyperv-tlfs.h>
> +#include <asm-generic/hyperv-defs.h>
>  
>  #define MAX_PAGE_BUFFER_COUNT				32
>  #define MAX_MULTIPAGE_BUFFER_COUNT			32 /* 128K */
> -- 
> 2.25.1
>