Re: [PATCH 1/3] IntelFrameworkPkg/LegacyBios.h: Add a macro to guarantee page 0 access

["Wang, Jian J" <jian.j.wang@intel.com>]

Good catch. I think it's a typo not on purpose. Many thanks!

> -----Original Message-----
> From: Ni, Ruiyu
> Sent: Wednesday, December 06, 2017 5:31 PM
> To: Wang, Jian J <jian.j.wang@intel.com>; edk2-devel@lists.01.org
> Cc: Kinney, Michael D <michael.d.kinney@intel.com>; Gao, Liming
> <liming.gao@intel.com>
> Subject: Re: [edk2] [PATCH 1/3] IntelFrameworkPkg/LegacyBios.h: Add a macro
> to guarantee page 0 access
> 
> On 12/6/2017 3:31 PM, Jian J Wang wrote:
> > Due to the introduction of NULL pointer detection feature, page 0 will be
> > disabled if the feature is enabled, which will cause legacy code failed to
> > update legacy data in page 0. This macro is introduced to make sure the
> > page 0 is enabled before those code and restore the original status of it
> > afterwards.
> >
> > Another reason to introduce this macro is to eliminate the dependency on
> > the PcdNullPointerDetectionPropertyMask. Because this is a new PCD, it
> > could cause some backward compatibility issue for some old packages.
> >
> > This macro will simply check if the page 0 is disabled or not. If it's
> > disabled, it will enable it before code updating page 0 and disable it
> > afterwards. Otherwise, this macro will do nothing to page 0.
> >
> > The usage of the macro will be look like (similar to DEBUG_CODE macro):
> >
> >      ACCESS_PAGE0_CODE(
> >        {
> >            <code accessing page 0>
> >        }
> >      );
> >
> > Cc: Liming Gao <liming.gao@intel.com>
> > Cc: Michael D Kinney <michael.d.kinney@intel.com>
> > Contributed-under: TianoCore Contribution Agreement 1.1
> > Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
> > ---
> >   IntelFrameworkPkg/Include/Protocol/LegacyBios.h | 34
> +++++++++++++++++++++++++
> >   1 file changed, 34 insertions(+)
> >
> > diff --git a/IntelFrameworkPkg/Include/Protocol/LegacyBios.h
> b/IntelFrameworkPkg/Include/Protocol/LegacyBios.h
> > index 641f101bce..f77c92ba21 100644
> > --- a/IntelFrameworkPkg/Include/Protocol/LegacyBios.h
> > +++ b/IntelFrameworkPkg/Include/Protocol/LegacyBios.h
> > @@ -1518,6 +1518,40 @@ struct _EFI_LEGACY_BIOS_PROTOCOL {
> >     EFI_LEGACY_BIOS_BOOT_UNCONVENTIONAL_DEVICE
> BootUnconventionalDevice;
> >   };
> >
> > +//
> > +// Legacy BIOS needs to access memory in page 0 (0-4095), which is disabled
> if
> > +// NULL pointer detection feature is enabled. Following macro can be used to
> > +// enable/disable page 0 before/after accessing it.
> > +//
> > +#define ACCESS_PAGE0_CODE(statements)                           \
> > +  do {                                                          \
> > +    EFI_STATUS                            Status_;              \
> > +    EFI_GCD_MEMORY_SPACE_DESCRIPTOR       Desc_;                \
> > +                                                                \
> > +    Status_ = gDS->GetMemorySpaceDescriptor (0, &Desc_);        \
> > +    if (!EFI_ERROR (Status_)) {                                 \
> > +      if ((Desc_.Attributes & EFI_MEMORY_RP) != 0) {            \
> > +        Status_ = gDS->SetMemorySpaceAttributes (               \
> > +                        0,                                      \
> > +                        EFI_PAGES_TO_SIZE(1),                   \
> > +                        Desc_.Attributes &= ~EFI_MEMORY_RP      \
> 
> &= is used here so Desc_.Attributes is updated to have RP cleared.
> Then the below if will be always FALSE.
> 
> > +                        );                                      \
> > +        ASSERT_EFI_ERROR (Status_);                             \
> > +      }                                                         \
> > +                                                                \
> > +      statements;                                               \
> > +                                                                \
> > +      if ((Desc_.Attributes & EFI_MEMORY_RP) != 0) {            \
> > +        Status_ = gDS->SetMemorySpaceAttributes (               \
> > +                        0,                                      \
> > +                        EFI_PAGES_TO_SIZE(1),                   \
> > +                        Desc_.Attributes                        \
> > +                        );                                      \
> > +        ASSERT_EFI_ERROR (Status_);                             \
> > +      }                                                         \
> > +    }                                                           \
> > +  } while (FALSE)
> > +
> >   extern EFI_GUID gEfiLegacyBiosProtocolGuid;
> >
> >   #endif
> >
> 
> 
> --
> Thanks,
> Ray