Hi Gerd Sorry for responding late. Using 5level paging when the below two conditions are both true: 1. CPU support 5level paging 2. Platform choose to use 5level paging. (by specifing macro USE_5_LEVEL_PAGE_TABLE)
There is an assumption that if platform choose to use 5level paging, then 5level paging should be supported by CPU. (Platform should know its CPU capability) So condition#1 is actually depends on condition#2. The condition#2 is decided at build time. If Platform choose to use 4level paging at build time, we can save 4K space by not creating the 5 level page. We can check the Cr4. LA57 to know if 4G - 12k is 4level or 5level paging when debugging after reset vector. In a word, current way can save 4K space in flash when using 4level paging. Please let me know if you have any other concern or consideration about this. Thanks. Thanks Zhiguang > -----Original Message----- > From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Gerd > Hoffmann > Sent: Monday, April 3, 2023 7:56 PM > To: Liu, Zhiguang <zhiguang....@intel.com> > Cc: devel@edk2.groups.io; Dong, Eric <eric.d...@intel.com>; Ni, Ray > <ray...@intel.com>; Kumar, Rahul R <rahul.r.ku...@intel.com>; De, > Debkumar <debkumar...@intel.com>; West, Catharine > <catharine.w...@intel.com> > Subject: Re: [edk2-devel] [PATCH 2/2] UefiCpuPkg: Support 5 level page > table in ResetVector > > On Mon, Apr 03, 2023 at 05:28:14PM +0800, Zhiguang Liu wrote: > > Use a macro USE_5_LEVEL_PAGE_TABLE to determine whether to create > > 5 level page table. Whether creating it or not, the highest level page > > table address is fixed. > > Can we create the 5level page table unconditionally? > > We should have the PML5 table @ fixed at 4G - 12k and the PML4 table fixed > at 4G - 16k then. Then ideally check processor capabilities and decide at > runtime whenever to use 4level or 5level paging. > > thanks, > Gerd > > > > > -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#102966): https://edk2.groups.io/g/devel/message/102966 Mute This Topic: https://groups.io/mt/98031298/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
