Re: [edk2-devel] [PATCH] UefiCpuPkg:Limit PhysicalAddressBits in speicial case

["duntan" <dun.tan@intel.com>]

Hi Gerd,

Thanks for your comments. I agree with your opinion. Will change the code and related comments in V2 patch.

Thanks,
Dun

-----Original Message-----
From: Gerd Hoffmann <kraxel@redhat.com> 
Sent: Wednesday, January 10, 2024 6:55 PM
To: Tan, Dun <dun.tan@intel.com>
Cc: devel@edk2.groups.io; Ni, Ray <ray.ni@intel.com>; Laszlo Ersek <lersek@redhat.com>; Kumar, Rahul R <rahul.r.kumar@intel.com>
Subject: Re: [PATCH] UefiCpuPkg:Limit PhysicalAddressBits in speicial case

On Wed, Jan 10, 2024 at 04:05:44PM +0800, Dun Tan wrote:
> When creating smm page table, limit maximum supported physical address 
> bits returned by
> CalculateMaximumSupportAddress() to 48 if 5-Level Paging is disabled.
> When 5-Level Paging is disabled and the PhysicalAddressBits retrived 
> from CPU HOB or CpuId is bigger than 48, only [0, 2^48 -1] range in 
> 52-bit physical address is mapped in page table.

I think this is wrong.  Virtual addresses are sign-extended, i.e. the virtual address space without 5-level paging is:

 0x0000000000000000 -> 0x00007fffffffffff and
 0xffff800000000000 -> 0xffffffffffffffff

Therefore identity-mapping works for [0, 2^47-1] only.

take care,
  Gerd



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