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.w...@intel.com>; edk2-devel@lists.01.org
> Cc: Kinney, Michael D <michael.d.kin...@intel.com>; Gao, Liming
> <liming....@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....@intel.com>
> > Cc: Michael D Kinney <michael.d.kin...@intel.com>
> > Contributed-under: TianoCore Contribution Agreement 1.1
> > Signed-off-by: Jian J Wang <jian.j.w...@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
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