Re: [PATCH v6] UefiCpuPkg\CpuSmm: Save & restore CR2 on-demand paging in SMM

["Zeng, Star" <star.zeng@intel.com>]

Not comment to functionality. But just some observations about code style.
Please check them inline.

> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of
> nkvangup
> Sent: Friday, March 29, 2019 12:58 PM
> To: edk2-devel@lists.01.org
> Cc: Yao, Jiewen <jiewen.yao@intel.com>; Dong, Eric <eric.dong@intel.com>;
> Laszlo Ersek <lersek@redhat.com>
> Subject: [edk2] [PATCH v6] UefiCpuPkg\CpuSmm: Save & restore CR2 on-
> demand paging in SMM
> 
> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=1593
> 
> For every SMI occurrence, save and restore CR2 register only when SMM
> on-demand paging support is enabled in 64 bit operation mode.
> This is not a bug but to have better improvement of code.
> 
> Patch5 is updated with separate functions for Save and Restore of CR2
> based on review feedback.
> 
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Vanguput Narendra K <narendra.k.vanguput@intel.com>
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Yao Jiewen <jiewen.yao@intel.com>
> ---
>  UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/PageTbl.c   | 26
> ++++++++++++++++++++++++++
>  UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c      |  9 ++++++---
>  UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h | 22
> ++++++++++++++++++++++
>  UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c    | 30
> ++++++++++++++++++++++++++++++
>  4 files changed, 84 insertions(+), 3 deletions(-)
> 
> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/PageTbl.c
> b/UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/PageTbl.c
> index b734a1ea8c..af96e42982 100644
> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/PageTbl.c
> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/PageTbl.c
> @@ -316,3 +316,29 @@ SetPageTableAttributes (
> 
>    return ;
>  }
> +
> +/**
> +  This function returns with no action for 32 bit.
> +
> +  @param[in]  *Cr2  Pointer to variable to hold CR2 register value

It will be more accurate with "@param[out]" according to https://edk2-docs.gitbooks.io/edk-ii-c-coding-standards-specification/content/5_source_files/57_c_programming.html#table-9-parameter-modifiers.

Same comment is also applied to other implementation or prototype in header file.

> +**/
> +VOID
> +SaveCr2 (
> +  UINTN  *Cr2

Align with the comments above, it will be better with "OUT UINTN  *Cr2"

Same comment is also applied to other implementation or prototype in header file.

> +  )
> +{
> +  return ;
> +}
> +
> +/**
> +  This function returns with no action for 32 bit.
> +
> +  @param[in]  Cr2  Value to write into CR2 register
> +**/
> +VOID
> +RestoreCr2 (
> +  UINTN  Cr2

It will be better with "IN UINTN  Cr2".

Same comment is also applied to other implementation or prototype in header file.

Thanks,
Star

> +  )
> +{
> +  return ;
> +}
> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
> b/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
> index 3b0b3b52ac..ce70f77709 100644
> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c
> @@ -1112,9 +1112,11 @@ SmiRendezvous (
>    ASSERT(CpuIndex < mMaxNumberOfCpus);
> 
>    //
> -  // Save Cr2 because Page Fault exception in SMM may override its value
> +  // Save Cr2 because Page Fault exception in SMM may override its value,
> +  // when using on-demand paging for above 4G memory.
>    //
> -  Cr2 = AsmReadCr2 ();
> +  Cr2 = 0;
> +  SaveCr2 (&Cr2);
> 
>    //
>    // Perform CPU specific entry hooks
> @@ -1253,10 +1255,11 @@ SmiRendezvous (
> 
>  Exit:
>    SmmCpuFeaturesRendezvousExit (CpuIndex);
> +
>    //
>    // Restore Cr2
>    //
> -  AsmWriteCr2 (Cr2);
> +  RestoreCr2 (Cr2);
>  }
> 
>  /**
> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h
> b/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h
> index 84efb22981..c9d147c8a1 100644
> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h
> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h
> @@ -1243,4 +1243,26 @@ EFIAPI
>  PiSmmCpuSmiEntryFixupAddress (
>   );
> 
> +/**
> +  This function reads CR2 register when on-demand paging is enabled
> +  for 64 bit and no action for 32 bit.
> +
> +  @param[in]  *Cr2  Pointer to variable to hold CR2 register value
> +**/
> +VOID
> +SaveCr2 (
> +  UINTN  *Cr2
> +  );
> +
> +/**
> +  This function writes into CR2 register when on-demand paging is enabled
> +  for 64 bit and no action for 32 bit.
> +
> +  @param[in]  Cr2  Value to write into CR2 register
> +**/
> +VOID
> +RestoreCr2 (
> +  UINTN  Cr2
> +  );
> +
>  #endif
> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c
> b/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c
> index 2c77cb47a4..6cb44fbbe5 100644
> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c
> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c
> @@ -1053,3 +1053,33 @@ SetPageTableAttributes (
> 
>    return ;
>  }
> +
> +/**
> +  This function reads CR2 register when on-demand paging is enabled
> +
> +  @param[in]  *Cr2  Pointer to variable to hold CR2 register value
> +**/
> +VOID
> +SaveCr2 (
> +  UINTN  *Cr2
> +  )
> +{
> +  if (!mCpuSmmStaticPageTable) {
> +    *Cr2 = AsmReadCr2 ();
> +  }
> +}
> +
> +/**
> +  This function restores CR2 register when on-demand paging is enabled
> +
> +  @param[in]  Cr2  Value to write into CR2 register
> +**/
> +VOID
> +RestoreCr2 (
> +  UINTN  Cr2
> +  )
> +{
> +  if ((!mCpuSmmStaticPageTable) && (Cr2 != 0)) {
> +    AsmWriteCr2 (Cr2);
> +  }
> +}
> --
> 2.16.2.windows.1
> 
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