Re: [Patch V2] MdePkg: Code optimization to SMM InternalAllocateAlignedPages

["Michael D Kinney" <michael.d.kinney@intel.com>]

Is this considered a critical bug for stable tag release?

Is there are HSD and if it is critical, all memory allocation lobs should be fixed.  Right?

Mike

> -----Original Message-----
> From: Ni, Ray <ray.ni@intel.com>
> Sent: Thursday, May 18, 2023 1:55 AM
> To: Tan, Dun <dun.tan@intel.com>; devel@edk2.groups.io
> Cc: Kinney, Michael D <michael.d.kinney@intel.com>; Gao, Liming
> <gaoliming@byosoft.com.cn>; Liu, Zhiguang <zhiguang.liu@intel.com>
> Subject: RE: [Patch V2] MdePkg: Code optimization to SMM
> InternalAllocateAlignedPages
> 
> Reviewed-by: Ray Ni <ray.ni@intel.com>
> 
> > -----Original Message-----
> > From: Tan, Dun <dun.tan@intel.com>
> > Sent: Thursday, May 18, 2023 3:31 PM
> > To: devel@edk2.groups.io
> > Cc: Ni, Ray <ray.ni@intel.com>; Kinney, Michael D
> > <michael.d.kinney@intel.com>; Gao, Liming <gaoliming@byosoft.com.cn>;
> Liu,
> > Zhiguang <zhiguang.liu@intel.com>
> > Subject: [Patch V2] MdePkg: Code optimization to SMM
> > InternalAllocateAlignedPages
> >
> > This commit is code optimization to InternalAllocateAlignedPages of
> > SmmMemoryAllocationLib which can reduce free memory fragments. Also
> > it can reduce one pre-allocation page.
> >
> > Let's take a simple example:
> > The expected pages size is 8KB, Alignment value is 8KB.
> >
> > In original InternalAllocateAlignedPages(), the first step is to
> > allocate 4 pages and then find the first 8KB-aligned address in
> > allocated 4 pages. If the upper limit address of allocated 4 pages
> > is already 8KB aligned, then the allocated 4 pages contains two
> > 8KB-aligned 8KB ranges. The lower 2 pages will be selected and
> > removed from free pages. Then the higher 2 pages will be free.
> > Since the whole memory allocation is from high address to low
> > address, then the higher 2 pages cann't be merged with other free
> > pages, causing the free memory fragments.
> >
> > However, when only allocate 3(2+2-1) pages, we can avoid the free
> > memory fragments in specific case. Also 3 pages must contain a
> > 8KB-aligned 8KB range, which meets the requirement. If the upper
> > limit address of allocated 3 pages is 8KB-aligned, then the higher
> > 2 pages range of allocated 3 pages is 8KB-aligned and will be
> > selected and removed from free pages. The remaining lower one page
> > of allocated 3 pages will be free and merged with left lower free
> > memory. This can reduce free memory fragments in smm.
> >
> > Signed-off-by: Dun Tan <dun.tan@intel.com>
> > Cc: Ray Ni <ray.ni@intel.com>
> > Cc: Michael D Kinney <michael.d.kinney@intel.com>
> > Cc: Liming Gao <gaoliming@byosoft.com.cn>
> > Cc: Zhiguang Liu <zhiguang.liu@intel.com>
> > ---
> >  MdePkg/Library/SmmMemoryAllocationLib/MemoryAllocationLib.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git
> a/MdePkg/Library/SmmMemoryAllocationLib/MemoryAllocationLib.c
> > b/MdePkg/Library/SmmMemoryAllocationLib/MemoryAllocationLib.c
> > index 3ab2c1ebfd..99a8259325 100644
> > --- a/MdePkg/Library/SmmMemoryAllocationLib/MemoryAllocationLib.c
> > +++ b/MdePkg/Library/SmmMemoryAllocationLib/MemoryAllocationLib.c
> > @@ -322,7 +322,7 @@ InternalAllocateAlignedPages (
> >      // Calculate the total number of pages since alignment is larger than
> page size.
> >      //
> >      AlignmentMask = Alignment - 1;
> > -    RealPages     = Pages + EFI_SIZE_TO_PAGES (Alignment);
> > +    RealPages     = Pages + EFI_SIZE_TO_PAGES (Alignment) - 1;
> >      //
> >      // Make sure that Pages plus EFI_SIZE_TO_PAGES (Alignment) does not
> > overflow.
> >      //
> > --
> > 2.31.1.windows.1