Re: [PATCH 14/15] asm-generic: hyperv: Use mshv headers conditionally. Add asm-generic/hyperv-defs.h

[Nuno Das Neves <nunodasneves@linux.microsoft.com>]

On 8/2/2023 5:48 PM, Wei Liu wrote:
> 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.
> 
Will fix, thanks.

>> 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.
> 

We do have some host-only interfaces in hyperv-tlfs.h that should not be there.
E.g. the create LP/VP hypercall inputs. We should drop them.

However, even if we fix that problem, the new headers still have conflicting
definitions, so need to be independent.
E.g. enum hv_message_type has many more members in the new headers.

We don't want to put anything not in the TLFS doc into hyperv-tlfs.h, even if it
can be ignored by the guest code.

>> +#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
>>