Re: [PATCH v9] UefiCpuPkg\CpuSmm: Save & restore CR2 on-demand paging in SMM

["Desimone, Nathaniel L" <nathaniel.l.desimone@intel.com>]

Hi Narendra,

I see that now, thank you. I now understand your patch.

Reviewed-by: Nate DeSimone <nathaniel.l.desimone@intel.com>

-----Original Message-----
From: Vanguput, Narendra K 
Sent: Monday, April 1, 2019 7:32 PM
To: Desimone, Nathaniel L <nathaniel.l.desimone@intel.com>; edk2-devel@lists.01.org
Cc: Yao, Jiewen <jiewen.yao@intel.com>; Dong, Eric <eric.dong@intel.com>; Laszlo Ersek <lersek@redhat.com>
Subject: RE: [edk2] [PATCH v9] UefiCpuPkg\CpuSmm: Save & restore CR2 on-demand paging in SMM

Hi Nate,

The 'PcdCpuSmmStaticPageTable' is only used in the X64 version of PageTbl.c  that's why I updated only for 64 bit. SMM always builds static page table for IA32.
Please refer my previous mail for more details.

Thanks,
Narendra

> -----Original Message-----
> From: Desimone, Nathaniel L
> Sent: Tuesday, April 2, 2019 5:57 AM
> To: Vanguput, Narendra K <narendra.k.vanguput@intel.com>; edk2- 
> devel@lists.01.org
> Cc: Yao, Jiewen <jiewen.yao@intel.com>; Dong, Eric 
> <eric.dong@intel.com>; Laszlo Ersek <lersek@redhat.com>
> Subject: RE: [edk2] [PATCH v9] UefiCpuPkg\CpuSmm: Save & restore CR2 
> on- demand paging in SMM
> 
> This patch seems to only add the IN/OUT decorators on function 
> parameters, which is a good change. However, it does not address any 
> of my previous
> comments:
> 
> 1. Why would you do this for 64 bit but not 32 bit?
> 2. Why don't you add the if statement to MpService.c instead of 
> spreading it to PageTbl.c?
> 3. What is the reason for this anyway? Adding the conditional is 
> probably more execution time than just reading CR2 always.
> 
> I also share Andrew's concern that in the case of a periodic SMI 
> happening during OS runtime, there is nothing preventing the handler 
> of the periodic SMI from clobbering the value of CR2, which could 
> potentially cause kernel panics once we return back from SMM to the 
> OS. I am not aware of any periodic SMIs in OVMF, so I don't believe 
> OVMF testing will catch these type of issues. I consider not doing the 
> save/restore in the 32 bit SMM to be dangerous, especially since all 
> recent platforms that I can think of don't use 32 bit SMM anymore, so any bug(s) introduced may go unnoticed for a long time.
> 
> Thanks,
> Nate
> 
> -----Original Message-----
> From: edk2-devel <edk2-devel-bounces@lists.01.org> On Behalf Of 
> nkvangup
> Sent: Monday, April 1, 2019 1:16 AM
> 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 v9] 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.
> 
> Patch6 - Removed Global Cr2 instead used function parameter.
> 
> Patch7 - Removed checking Cr2 with 0 as per feedback.
> 
> Patch8 and 9 - Aligned with EDK2 Coding style.
> 
> 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..d1e146a70c 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[out]  *Cr2  Pointer to variable to hold CR2 register value.
> +**/
> +VOID
> +SaveCr2 (
> +  OUT UINTN  *Cr2
> +  )
> +{
> +  return ;
> +}
> +
> +/**
> +  This function returns with no action for 32 bit.
> +
> +  @param[in]  Cr2  Value to write into CR2 register.
> +**/
> +VOID
> +RestoreCr2 (
> +  IN UINTN  Cr2
> +  )
> +{
> +  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..38f9104117 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[out]  *Cr2  Pointer to variable to hold CR2 register value.
> +**/
> +VOID
> +SaveCr2 (
> +  OUT 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 (
> +  IN UINTN  Cr2
> +  );
> +
>  #endif
> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c
> b/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c
> index 2c77cb47a4..95eaf0b016 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[out]  *Cr2  Pointer to variable to hold CR2 register value.
> +**/
> +VOID
> +SaveCr2 (
> +  OUT 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 (
> +  IN UINTN  Cr2
> +  )
> +{
> +  if (!mCpuSmmStaticPageTable) {
> +    AsmWriteCr2 (Cr2);
> +  }
> +}
> --
> 2.16.2.windows.1
> 
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