Re: [PATCH 05/13] MdePkg/Library/BaseLib/AArch64: Add AsmLfence function

["Gao, Liming" <liming.gao@intel.com>]

Ard:
  My first comment is to suggest updating the caller code for the arch specific code.  But, there are two drivers that have the same usage. This way will introduce the duplicated code logic. So, I suggest another way to extend  AsmLfence() API scope for the different ARCHs. If you think it brings the confuse, I just think another way to resolve this case in the caller code. 

#if defined (MDE_CPU_IA32) || defined (MDE_CPU_X64)
AsmLfence();
#else
MemoryFence()
#endif

Thanks
Liming
>-----Original Message-----
>From: Ard Biesheuvel [mailto:ard.biesheuvel@linaro.org]
>Sent: Friday, December 14, 2018 9:54 PM
>To: Jagadeesh Ujja <jagadeesh.ujja@arm.com>; Leif Lindholm
><leif.lindholm@linaro.org>
>Cc: edk2-devel@lists.01.org; Gao, Liming <liming.gao@intel.com>; Zhang,
>Chao B <chao.b.zhang@intel.com>
>Subject: Re: [PATCH 05/13] MdePkg/Library/BaseLib/AArch64: Add
>AsmLfence function
>
>On Fri, 14 Dec 2018 at 13:13, Jagadeesh Ujja <jagadeesh.ujja@arm.com>
>wrote:
>>
>> Variable service driver includes a call to AsmLfence. To reuse this
>> driver on AArch64 based platforms, add an implementation of AsmLfence
>> that acts as a wrapper on the AArch64 specific MemoryFence function.
>>
>> Contributed-under: TianoCore Contribution Agreement 1.1
>> Signed-off-by: Jagadeesh Ujja <jagadeesh.ujja@arm.com>
>> ---
>>  MdePkg/Include/Library/BaseLib.h             | 33 +++++++++------
>>  MdePkg/Library/BaseLib/AArch64/AsmLfence.S   | 42
>++++++++++++++++++++
>>  MdePkg/Library/BaseLib/AArch64/AsmLfence.asm | 41
>+++++++++++++++++++
>>  MdePkg/Library/BaseLib/BaseLib.inf           |  2 +
>>  4 files changed, 105 insertions(+), 13 deletions(-)
>>
>> diff --git a/MdePkg/Include/Library/BaseLib.h
>b/MdePkg/Include/Library/BaseLib.h
>> index 8cc0869..ca961ee 100644
>> --- a/MdePkg/Include/Library/BaseLib.h
>> +++ b/MdePkg/Include/Library/BaseLib.h
>> @@ -7697,19 +7697,6 @@ AsmWriteTr (
>>    );
>>
>>  /**
>> -  Performs a serializing operation on all load-from-memory instructions that
>> -  were issued prior the AsmLfence function.
>> -
>> -  Executes a LFENCE instruction. This function is only available on IA-32 and
>x64.
>> -
>> -**/
>> -VOID
>> -EFIAPI
>> -AsmLfence (
>> -  VOID
>> -  );
>> -
>> -/**
>>    Patch the immediate operand of an IA32 or X64 instruction such that the
>byte,
>>    word, dword or qword operand is encoded at the end of the instruction's
>>    binary representation.
>> @@ -7752,4 +7739,24 @@ PatchInstructionX86 (
>>    );
>>
>>  #endif // defined (MDE_CPU_IA32) || defined (MDE_CPU_X64)
>> +
>> +#if defined (MDE_CPU_IA32) || defined (MDE_CPU_X64) || defined
>(MDE_CPU_AARCH64)
>> +
>> +/**
>> +  Performs a serializing operation on all load-from-memory instructions that
>> +  were issued prior the AsmLfence function.
>> +
>> +  In case of IA-32 and x64, Executes a LFENCE instruction.
>> +
>> +  In case of AArch64 this acts as a wrapper on the AArch64
>> +  specific MemoryFence function
>> +
>> +**/
>> +VOID
>> +EFIAPI
>> +AsmLfence (
>> +  VOID
>> +  );
>> +
>> +#endif  // defined (MDE_CPU_IA32) || defined (MDE_CPU_X64) ||
>defined (MDE_CPU_AARCH64)
>>  #endif // !defined (__BASE_LIB__)
>> diff --git a/MdePkg/Library/BaseLib/AArch64/AsmLfence.S
>b/MdePkg/Library/BaseLib/AArch64/AsmLfence.S
>> new file mode 100644
>> index 0000000..2fd804b
>> --- /dev/null
>> +++ b/MdePkg/Library/BaseLib/AArch64/AsmLfence.S
>> @@ -0,0 +1,42 @@
>> +##------------------------------------------------------------------------------
>> +#
>> +# AsmLfence() for AArch64
>> +#
>> +# Copyright (c) 2013-2018, ARM Ltd. All rights reserved.
>> +#
>> +# This program and the accompanying materials
>> +# are licensed and made available under the terms and conditions of the
>BSD License
>> +# which accompanies this distribution.  The full text of the license may be
>found at
>> +# http://opensource.org/licenses/bsd-license.php.
>> +#
>> +# THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS"
>BASIS,
>> +# WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER
>EXPRESS OR IMPLIED.
>> +#
>> +##------------------------------------------------------------------------------
>> +
>> +.text
>> +.p2align 2
>> +
>> +GCC_ASM_EXPORT(AsmLfence)
>> +
>> +# IMPORT
>> +GCC_ASM_IMPORT(MemoryFence)
>> +
>> +#/**
>> +#  Used to serialize load and store operations.
>> +#
>> +#  All loads and stores that proceed calls to this function are guaranteed to
>be
>> +#  globally visible when this function returns.
>> +#
>> +#**/
>> +#VOID
>> +#EFIAPI
>> +#AsmLfence (
>> +#  VOID
>> +#  );
>> +#
>> +ASM_PFX(AsmLfence):
>> +    stp   x29, x30, [sp, #-16]!
>> +    bl MemoryFence
>> +    ldp   x29, x30, [sp], #0x10
>> +    ret
>
>Any reason we can't simply do
>
>b MemoryFence
>
>here?
>
>Also, why I understand the rationale, I still think it would be better
>to change callers of the [x86 specific] AsmLfence() than to introduce
>an alias of MemoryFence() for architectures where Lfence is not
>defined.
>
>This is not only about tidiness, but also about potentially having
>different semantics, which we can't provide in general on ARM, but
>only in particular cases [such as the code that is modified in this
>series]
>
>In other words, newly introduced occurrences of AsmLfence() now have
>to be audited for being appropriate on AArc64 if they are added to
>generic code.
>
>
>> diff --git a/MdePkg/Library/BaseLib/AArch64/AsmLfence.asm
>b/MdePkg/Library/BaseLib/AArch64/AsmLfence.asm
>> new file mode 100644
>> index 0000000..7dd5659
>> --- /dev/null
>> +++ b/MdePkg/Library/BaseLib/AArch64/AsmLfence.asm
>> @@ -0,0 +1,41 @@
>> +;------------------------------------------------------------------------------
>> +;
>> +; AsmLfence() for AArch64
>> +;
>> +; Copyright (c) 2013-2018, ARM Ltd. All rights reserved.
>> +;
>> +; This program and the accompanying materials
>> +; are licensed and made available under the terms and conditions of the
>BSD License
>> +; which accompanies this distribution.  The full text of the license may be
>found at
>> +; http://opensource.org/licenses/bsd-license.php.
>> +;
>> +; THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS"
>BASIS,
>> +; WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER
>EXPRESS OR IMPLIED.
>> +;
>> +;------------------------------------------------------------------------------
>> +
>> +  EXPORT AsmLfence
>> +  AREA BaseLib_LowLevel, CODE, READONLY
>> +  # IMPORT
>> +  GCC_ASM_IMPORT(MemoryFence)
>> +
>> +;/**
>> +;  Used to serialize load and store operations.
>> +;
>> +;  All loads and stores that proceed calls to this function are guaranteed to
>be
>> +;  globally visible when this function returns.
>> +;
>> +;**/
>> +;VOID
>> +;EFIAPI
>> +;AsmLfence (
>> +;  VOID
>> +;  );
>> +;
>> +AsmLfence
>> +    stp   x29, x30, [sp, #-16]!
>> +    bl MemoryFence
>> +    ldp   x29, x30, [sp], #0x10
>> +    ret
>> +
>> +  END
>> diff --git a/MdePkg/Library/BaseLib/BaseLib.inf
>b/MdePkg/Library/BaseLib/BaseLib.inf
>> index b84e583..b7d7bcb 100644
>> --- a/MdePkg/Library/BaseLib/BaseLib.inf
>> +++ b/MdePkg/Library/BaseLib/BaseLib.inf
>> @@ -585,6 +585,7 @@
>>    Math64.c
>>
>>    AArch64/MemoryFence.S             | GCC
>> +  AArch64/AsmLfence.S               | GCC
>>    AArch64/SwitchStack.S             | GCC
>>    AArch64/EnableInterrupts.S        | GCC
>>    AArch64/DisableInterrupts.S       | GCC
>> @@ -593,6 +594,7 @@
>>    AArch64/CpuBreakpoint.S           | GCC
>>
>>    AArch64/MemoryFence.asm           | MSFT
>> +  AArch64/AsmLfence.asm             | MSFT
>>    AArch64/SwitchStack.asm           | MSFT
>>    AArch64/EnableInterrupts.asm      | MSFT
>>    AArch64/DisableInterrupts.asm     | MSFT
>> --
>> 2.7.4
>>