Re: [edk2-devel] [PATCH 1/1] MdeModulePkg/VariableRuntimeDxe: avoid double VA conversion of FVB protocol

["Samer El-Haj-Mahmoud" <samer.el-haj-mahmoud@arm.com>]

Late to the party, but I confirm that this fixes the SetVariable() runtime calls on Solid Run Honeycomb LX2 (confirmed from multiple distros)

Tested-by: Samer El-Haj-Mahmoud <Samer.El-Haj-Mahmoud@arm.com>



> -----Original Message-----
> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Laszlo
> Ersek via groups.io
> Sent: Tuesday, March 16, 2021 11:58 AM
> To: Ard Biesheuvel <ardb@kernel.org>; devel@edk2.groups.io
> Cc: liming.gao@intel.com; Jon (jon@solid-run.com) <jon@solid-run.com>;
> leif@nuviainc.com
> Subject: Re: [edk2-devel] [PATCH 1/1] MdeModulePkg/VariableRuntimeDxe:
> avoid double VA conversion of FVB protocol
>
> On 03/13/21 00:05, Ard Biesheuvel wrote:
> > For historical reasons, the VariableRuntimeDxe performs virtual
> > address conversion on the FVB protocol member pointers of the protocol
> > instance that backs the EFI variable store. However, the driver that
> > produces the actual instance should be doing this, as it is the owner,
> > and provides the actual implementation of those methods.
> >
> > Unfortunately, we cannot simply change this: existing drivers may rely
> > on this behavior, and so the variable driver should take care to only
> > convert the pointers when necessary, but leave them alone when the
> > owner is taking care of this.
> >
> > The virtual address switch event can be delivered in arbitrary order,
> > and so we should take care of this in a way that does not rely on
> > whether this driver converts its pointers either before or after the
> > owner of the FVB protocol receives the event.
> >
> > So let's not convert the pointers at all when the event is delivered,
> > but record the converted addresses in a shadow FVB protocol. This way,
> > we can check when the variable driver is invoked at runtime whether
> > the switch has occurred or not, and perform the switch if it hasn't.
> >
> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > ---
> > Build tested only.
> >
> >  MdeModulePkg/Universal/Variable/RuntimeDxe/VariableDxe.c | 50
> > +++++++++++++++++---
> >  1 file changed, 43 insertions(+), 7 deletions(-)
> >
> > diff --git a/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableDxe.c
> > b/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableDxe.c
> > index 0fca0bb2a9b5..3d83ac4452ee 100644
> > --- a/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableDxe.c
> > +++ b/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableDxe.c
> > @@ -37,6 +37,8 @@ EDKII_VAR_CHECK_PROTOCOL            mVarCheck
> = { VarCheckRegis
> >                                                                      VarCheckVariablePropertySet,
> >
> > VarCheckVariablePropertyGet };
> >
> > +STATIC EFI_FIRMWARE_VOLUME_BLOCK_PROTOCOL
> mFvbProtocolShadow;
> > +
> >  /**
> >    Some Secure Boot Policy Variable may update following other variable
> changes(SecureBoot follows PK change, etc).
> >    Record their initial State when variable write service is ready.
> > @@ -105,8 +107,26 @@ AcquireLockOnlyAtBootTime (
> >    IN EFI_LOCK                             *Lock
> >    )
> >  {
>
> (1) Why is AcquireLockOnlyAtBootTime() the best place to add this?
>
> (Considering especially the leading comment, "This is a temperary function
> that will be removed when EfiAcquireLock() in UefiLib can handle the call in
> UEFI Runtimer driver in RT phase".)
>
> Obviously, I don't want to create more work for you! I just feel that, if this is
> not the best place, we shouldn't overload this function with a new
> responsibility.
>
> > +  EFI_FIRMWARE_VOLUME_BLOCK_PROTOCOL  *FvbInstance;
> > +
> >    if (!AtRuntime ()) {
> >      EfiAcquireLock (Lock);
> > +  } else {
> > +    //
> > +    // Check whether we need to swap in the converted pointer values for
> the
> > +    // FVB protocol methods
> > +    //
> > +    FvbInstance = mVariableModuleGlobal->FvbInstance;
> > +    if (FvbInstance != NULL &&
> > +        FvbInstance->GetBlockSize != mFvbProtocolShadow.GetBlockSize)
> > + {
>
> (2) It occurs to me that the following pattern (in a single-threaded
> environment):
>
>     if (a != b) {
>       a = b;
>     }
>
> is just:
>
>   a = b;
>
> (the small CPU cost notwithstanding).
>
> And that puts this patch in a bit different light: it's not that we may or may
> not convert. Instead, we *always* convert, the question is *when* we apply
> the result of the conversion.
>
> Functionally, there is no difference, but to me mentally, there'd be a
> difference, if we said "delay applying the runtime conversion until first call".
>
> Anyway... just wanted to highlight this: we could drop the GetBlockSize
> funcptr comparison. But, we don't have to.
>
> Given the reviews from Liming and Hao -- and thank you in the first place for
> writing the patch! --, I won't really ask for a v2. I'd just somehow prefer the
> compat logic to be elsewhere, rather than in AcquireLockOnlyAtBootTime().
> In the first place, I'm not clear what we currently use
> AcquireLockOnlyAtBootTime() for.
>
> Up to the maintainers to decide whether this justifies v2. If not:
>
> Acked-by: Laszlo Ersek <lersek@redhat.com>
>
> Thanks
> Laszlo
>
> > +      FvbInstance->GetBlockSize       = mFvbProtocolShadow.GetBlockSize;
> > +      FvbInstance->GetPhysicalAddress =
> mFvbProtocolShadow.GetPhysicalAddress;
> > +      FvbInstance->GetAttributes      = mFvbProtocolShadow.GetAttributes;
> > +      FvbInstance->SetAttributes      = mFvbProtocolShadow.SetAttributes;
> > +      FvbInstance->Read               = mFvbProtocolShadow.Read;
> > +      FvbInstance->Write              = mFvbProtocolShadow.Write;
> > +      FvbInstance->EraseBlocks        = mFvbProtocolShadow.EraseBlocks;
> > +    }
> >    }
> >  }
> >
> > @@ -247,13 +267,22 @@ VariableClassAddressChangeEvent (
> >    UINTN          Index;
> >
> >    if (mVariableModuleGlobal->FvbInstance != NULL) {
> > -    EfiConvertPointer (0x0, (VOID **) &mVariableModuleGlobal-
> >FvbInstance->GetBlockSize);
> > -    EfiConvertPointer (0x0, (VOID **) &mVariableModuleGlobal-
> >FvbInstance->GetPhysicalAddress);
> > -    EfiConvertPointer (0x0, (VOID **) &mVariableModuleGlobal-
> >FvbInstance->GetAttributes);
> > -    EfiConvertPointer (0x0, (VOID **) &mVariableModuleGlobal-
> >FvbInstance->SetAttributes);
> > -    EfiConvertPointer (0x0, (VOID **) &mVariableModuleGlobal-
> >FvbInstance->Read);
> > -    EfiConvertPointer (0x0, (VOID **) &mVariableModuleGlobal-
> >FvbInstance->Write);
> > -    EfiConvertPointer (0x0, (VOID **) &mVariableModuleGlobal-
> >FvbInstance->EraseBlocks);
> > +    //
> > +    // This module did not produce the FVB protocol instance that provides
> the
> > +    // variable store, so it should not be the one performing the pointer
> > +    // conversion on its members. However, some FVB protocol
> implementations
> > +    // may rely on this behavior, which was present in older versions of this
> > +    // driver, so we need to perform the conversion if the protocol
> producer
> > +    // fails to do so. So let's record the converted values now, and swap
> them
> > +    // in later if they haven't changed values.
> > +    //
> > +    EfiConvertPointer (0x0, (VOID
> **)&mFvbProtocolShadow.GetBlockSize);
> > +    EfiConvertPointer (0x0, (VOID
> **)&mFvbProtocolShadow.GetPhysicalAddress);
> > +    EfiConvertPointer (0x0, (VOID
> **)&mFvbProtocolShadow.GetAttributes);
> > +    EfiConvertPointer (0x0, (VOID
> **)&mFvbProtocolShadow.SetAttributes);
> > +    EfiConvertPointer (0x0, (VOID **)&mFvbProtocolShadow.Read);
> > +    EfiConvertPointer (0x0, (VOID **)&mFvbProtocolShadow.Write);
> > +    EfiConvertPointer (0x0, (VOID
> > + **)&mFvbProtocolShadow.EraseBlocks);
> >      EfiConvertPointer (0x0, (VOID **) &mVariableModuleGlobal-
> >FvbInstance);
> >    }
> >    EfiConvertPointer (0x0, (VOID **)
> > &mVariableModuleGlobal->PlatformLangCodes);
> > @@ -454,6 +483,13 @@ FtwNotificationEvent (
> >    }
> >    mVariableModuleGlobal->FvbInstance = FvbProtocol;
> >
> > +  //
> > +  // Store the boot time values of the function pointers so we can
> > + compare  // them later. This is needed to avoid double conversion
> > + during the call  // to SetVirtualAddressMap.
> > +  //
> > +  CopyMem (&mFvbProtocolShadow, FvbProtocol, sizeof
> > + mFvbProtocolShadow);
> > +
> >    //
> >    // Mark the variable storage region of the FLASH as RUNTIME.
> >    //
> >
>
>
>
> 
>

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