Re: [PATCH v4 1/7] ArmPkg/CpuDxe: ignore attribute changes during SyncCacheConfig()

[Leif Lindholm <leif.lindholm@linaro.org>]

On Mon, Feb 27, 2017 at 03:33:56PM +0000, Ard Biesheuvel wrote:
> On 27 February 2017 at 15:32, Leif Lindholm <leif.lindholm@linaro.org> wrote:
> > On Mon, Feb 27, 2017 at 02:38:05PM +0000, Ard Biesheuvel wrote:
> >> To prevent the initial MMU->GCD memory space map synchronization from
> >> stripping permissions attributes [which we cannot use in the GCD memory
> >> space map, unfortunately], implement the same approach as x86, and ignore
> >> SetMemoryAttributes() calls during the time SyncCacheConfig() is in
> >> progress. This is a horrible hack, but is currently the only way we can
> >> implement strict permissions on arbitrary memory regions [as opposed to
> >> PE/COFF text/data sections only]
> >
> > Sounds like another excellent argument for why this CpuDxe should be
> > cosying up with the UefiCpuPkg one longer-term.
> >
> 
> I suppose so, yes.
> 
> >> Contributed-under: TianoCore Contribution Agreement 1.0
> >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> >> Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
> >> ---
> >>  ArmPkg/Drivers/CpuDxe/CpuDxe.c       | 3 +++
> >>  ArmPkg/Drivers/CpuDxe/CpuDxe.h       | 1 +
> >>  ArmPkg/Drivers/CpuDxe/CpuMmuCommon.c | 4 ++++
> >>  3 files changed, 8 insertions(+)
> >>
> >> diff --git a/ArmPkg/Drivers/CpuDxe/CpuDxe.c b/ArmPkg/Drivers/CpuDxe/CpuDxe.c
> >> index 5aa5b874144a..1955d1dece03 100644
> >> --- a/ArmPkg/Drivers/CpuDxe/CpuDxe.c
> >> +++ b/ArmPkg/Drivers/CpuDxe/CpuDxe.c
> >> @@ -17,6 +17,7 @@
> >>
> >>  #include <Guid/IdleLoopEvent.h>
> >>
> >> +BOOLEAN                   gIsFlushingGCD;
> >
> > OK, I am unable to not bikeshed this:
> > The behaviour you're copying is implemented via a variable called
> > mIsFlushingGCD. Why change the prefix? Surely we're not looking to
> > export this variable any further in ARM?
> >
> 
> Because it is not local the one compilation unit, that's all. It is
> not in a library, so in that sense, it is guaranteed to remain local
> to this module, if that is any consolation.

Ah, excellent.

So, from how I read the coding standards (section 4.4), 'm' would
still be the appropriate prefix:
"A module variable is intended to only be accessed across a small set of
related routines that have strict rules for accessing the data; in
effect, constrained to the set of files described within a single .inf
file."

Regards,

Leif

> >>
> >>  /**
> >>    This function flushes the range of addresses from Start to Start+Length
> >> @@ -261,7 +262,9 @@ CpuDxeInitialize (
> >>    // and that calls EFI_CPU_ARCH_PROTOCOL.SetMemoryAttributes, so this code needs to go
> >>    // after the protocol is installed
> >>    //
> >> +  gIsFlushingGCD = TRUE;
> >>    SyncCacheConfig (&mCpu);
> >> +  gIsFlushingGCD = FALSE;
> >>
> >>    // If the platform is a MPCore system then install the Configuration Table describing the
> >>    // secondary core states
> >> diff --git a/ArmPkg/Drivers/CpuDxe/CpuDxe.h b/ArmPkg/Drivers/CpuDxe/CpuDxe.h
> >> index a00fc3064362..085e4cab2921 100644
> >> --- a/ArmPkg/Drivers/CpuDxe/CpuDxe.h
> >> +++ b/ArmPkg/Drivers/CpuDxe/CpuDxe.h
> >> @@ -37,6 +37,7 @@
> >>  #include <Protocol/DebugSupportPeriodicCallback.h>
> >>  #include <Protocol/LoadedImage.h>
> >>
> >> +extern BOOLEAN gIsFlushingGCD;
> >
> > Eew ... this suggest we are.
> >
> > /
> >     Leif
> >
> >>
> >>  /**
> >>    This function registers and enables the handler specified by InterruptHandler for a processor
> >> diff --git a/ArmPkg/Drivers/CpuDxe/CpuMmuCommon.c b/ArmPkg/Drivers/CpuDxe/CpuMmuCommon.c
> >> index ebe593d1c325..6dfec7e55888 100644
> >> --- a/ArmPkg/Drivers/CpuDxe/CpuMmuCommon.c
> >> +++ b/ArmPkg/Drivers/CpuDxe/CpuMmuCommon.c
> >> @@ -188,6 +188,10 @@ CpuSetMemoryAttributes (
> >>    UINTN       RegionLength;
> >>    UINTN       RegionArmAttributes;
> >>
> >> +  if (gIsFlushingGCD) {
> >> +    return EFI_SUCCESS;
> >> +  }
> >> +
> >>    if ((BaseAddress & (SIZE_4KB - 1)) != 0) {
> >>      // Minimum granularity is SIZE_4KB (4KB on ARM)
> >>      DEBUG ((EFI_D_PAGE, "CpuSetMemoryAttributes(%lx, %lx, %lx): Minimum ganularity is SIZE_4KB\n", BaseAddress, Length, EfiAttributes));
> >> --
> >> 2.7.4
> >>