Re: [edk2-devel] [PATCH 1/1] MdePkg/BaseLib: Add SpeculationBarrier implementation for RiscV64

["Sunil V L" <sunilvl@ventanamicro.com>]

On Mon, May 29, 2023 at 01:51:46PM +0800, Li, Yong wrote:
> 
> Hi Sunil,
> 
> Could you help review this my first patch to edk2 community for RiscV,  this is the change to MdePkg/Library/BaseLib/RiscV64. 
> Since it is for RiscV specific, I guess you are the only maintainer per the Maintainers.txt  ?
> Please let me know if need additional reviewer.  
> 
> Thanks in advance for your time and kind helping for this first patch.
> 
Hi Yong,

Thank you for the patch!

Just one typo in the commit text and one question below. Otherwise, LGTM.

> 
> On 2023/5/29 13:24, Li, Yong wrote:
> > Impelement the SpeculationBarrier with implementations consisting of

typo - "Implement"

> > fence instruction which provides finer-grain memory orderings.
> > Perform Data Barrier in RiscV: fence rw,rw
> > Perform Instruction Barrier in RiscV: fence.i; fence r,r
> > More detail is in Chapter 17, RVWMO Memory Consistency Model
> > https://github.com/riscv/riscv-isa-manual
> > 
> > This API is first introduced in the below commits for IA32 and x64
> > https://github.com/tianocore/edk2/commit/d9f1cac51bd354507e880e614d11a1dc160d38a3
> > https://github.com/tianocore/edk2/commit/e83d841fdc2878959185c4c6cc38a7a1e88377a4
> > and below the commit for ARM and AArch64 implementation
> > https://github.com/tianocore/edk2/commit/c0959b4426b2da45cdb8146a5116bb4fd9b86534
> > 
> > This commit is to add the RiscV64 implementation which will be used by
> > variable service under Variable/RuntimeDxe
> > 
> > Cc: Andrei Warkentin <andrei.warkentin@intel.com>
> > Cc: Evan Chai <evan.chai@intel.com>
> > Cc: Sunil V L <sunilvl@ventanamicro.com>
> > Cc: Tuan Phan <tphan@ventanamicro.com>
> > Signed-off-by: Yong Li <yong.li@intel.com>
> > ---
> >  MdePkg/Library/BaseLib/BaseLib.inf            |  1 +
> >  .../BaseLib/RiscV64/SpeculationBarrier.S      | 34 +++++++++++++++++++
> >  2 files changed, 35 insertions(+)
> >  create mode 100644 MdePkg/Library/BaseLib/RiscV64/SpeculationBarrier.S
> > 
> > diff --git a/MdePkg/Library/BaseLib/BaseLib.inf b/MdePkg/Library/BaseLib/BaseLib.inf
> > index 3a48492b1a01..03c7b02e828b 100644
> > --- a/MdePkg/Library/BaseLib/BaseLib.inf
> > +++ b/MdePkg/Library/BaseLib/BaseLib.inf
> > @@ -404,6 +404,7 @@ [Sources.RISCV64]
> >    RiscV64/CpuScratch.S              | GCC
> >    RiscV64/ReadTimer.S               | GCC
> >    RiscV64/RiscVMmu.S                | GCC
> > +  RiscV64/SpeculationBarrier.S      | GCC
> >  
> >  [Sources.LOONGARCH64]
> >    Math64.c
> > diff --git a/MdePkg/Library/BaseLib/RiscV64/SpeculationBarrier.S b/MdePkg/Library/BaseLib/RiscV64/SpeculationBarrier.S
> > new file mode 100644
> > index 000000000000..581a7653996f
> > --- /dev/null
> > +++ b/MdePkg/Library/BaseLib/RiscV64/SpeculationBarrier.S
> > @@ -0,0 +1,34 @@
> > +##------------------------------------------------------------------------------
> > +#
> > +# SpeculationBarrier() for RISCV64
> > +#
> > +# Copyright (c) 2023, Intel Corporation. All rights reserved.
> > +#
> > +# SPDX-License-Identifier: BSD-2-Clause-Patent
> > +#
> > +##------------------------------------------------------------------------------
> > +
> > +.text
> > +.p2align 2
> > +
> > +ASM_GLOBAL ASM_PFX(SpeculationBarrier)
> > +
> > +
> > +#/**
> > +#  Uses as a barrier to stop speculative execution.
> > +#
> > +#  Ensures that no later instruction will execute speculatively, until all prior
> > +#  instructions have completed.
> > +#
> > +#**/
> > +#VOID
> > +#EFIAPI
> > +#SpeculationBarrier (
> > +#  VOID
> > +#  );
> > +#
> > +ASM_PFX(SpeculationBarrier):
> > +    fence rw,rw

Don't we need fence iorw, iorw?

Thanks,
Sunil

> > +    fence.i
> > +    fence r,r
> > +    ret