Re: [RFC PATCH 3/7] MdeModulePkg/Dxe/Page: take MAX_ALLOC_ADDRESS into account

["Gao, Liming" <liming.gao@intel.com>]

Ard:
  I prefer to define MAX_ALLOC_ADDRESS together with MAX_ADDRESS in ProcessorBind.h. I don't want to leave the choice to override MAX_ALLOC_ADDRESS definition. 

Thanks
Liming
> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of Ard Biesheuvel
> Sent: Monday, December 10, 2018 3:23 PM
> To: Wang, Jian J <jian.j.wang@intel.com>
> Cc: Andrew Jones <drjones@redhat.com>; Wu, Hao A <hao.a.wu@intel.com>; edk2-devel@lists.01.org; Gao, Liming
> <liming.gao@intel.com>; Kinney, Michael D <michael.d.kinney@intel.com>; Laszlo Ersek <lersek@redhat.com>
> Subject: Re: [edk2] [RFC PATCH 3/7] MdeModulePkg/Dxe/Page: take MAX_ALLOC_ADDRESS into account
> 
> On Mon, 10 Dec 2018 at 03:04, Wang, Jian J <jian.j.wang@intel.com> wrote:
> >
> > Hi Ard,
> >
> > I think MAX_ALLOC_ADDRESS will affect other archs besides ARM. Please do enough
> > test for them (IA32/X64 for my concern).
> >
> 
> For all other architectures, MAX_ADDRESS == MAX_ALLOC_ADDRESS is
> always true, so these changes only affect AARCH64.
> 
> > In addition, do you think it's safer to replace MAX_ADDRESS with MAX_ALLOC_ADDRESS
> > in MemoryAllocationLib like following situation?
> >
> > (MdeModulePkg\Library\DxeCoreMemoryAllocationLib\MemoryAllocationLib.c)
> > VOID *
> > InternalAllocateCopyPool (
> >   IN EFI_MEMORY_TYPE  PoolType,
> >   IN UINTN            AllocationSize,
> >   IN CONST VOID       *Buffer
> >   )
> > {
> >   VOID  *Memory;
> >
> >   ASSERT (Buffer != NULL);
> >   ASSERT (AllocationSize <= (MAX_ADDRESS - (UINTN) Buffer + 1));
> >   ...
> 
> This assert ensures that the copied buffer does not extend across the
> end of the address space and wraps. This is a separate concern, and is
> similar to numerous other occurrences of MAX_ADDRESS that maybe we
> should update as well at some point. However, it does not affect page
> allocation at all, it only puts an upper bound on the *size* of the
> allocation. So the changes as they are will be sufficient to ensure
> that AllocateCopyPool() does not allocate from a region that is not
> addressable by the CPU.
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