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

["Laszlo Ersek" <lersek@redhat.com>]

On 1/10/24 11:54, Gerd Hoffmann wrote:
> 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.

I'd have never noticed this. I'll happily defer reviewing this patch to
you then! :)

Thanks!
Laszlo



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