On Wed, Jan 18, 2023 at 01:13:43AM +0000, Zhiguang Liu wrote: > Thanks all for reviewing, and I will send a new version to address the > comment. > > As for Gerd's question, let me explain. > Let's see one example, that the CPU has SizeOfMemorySpace >48, but the CPU > doesn't enable 5 level paging. > The purpose of the current function InitPaging is to modify existing > page table. To use the same logic to handle both 5 level and 4 level > paging, for 4 level paging, the logic will create a false 5 level > paging entry to treat it like a 5 level page table.
Yes. Same for 3-level paging btw. There are always page tables for 5 levels, but the higher levels might be unused. > This way, the > number of 5 level paging should always be one. If we use > SizeOfMemorySpace to calculate the 5 level paging entry count, we will > get number more than one. However, as I just mentioned, we only > create one false 5 level paging entry, system may hang when we try to > access the second 5 level paging entry. If 5-level paging is turned off the CPU should not see what you are doing with the page tables for the second (and higher) 5-level entry. So, limiting the number of 5-level entries does make sense. Higher entries are not used, so it's pointless work. But that doesn't answer the question: Why does that fix the system hanging? I just can't see a reason for that when looking through the InitPaging code. I suspect this might hide a bug somewhere else. Related: We got UefiCpuPkg/Library/CpuPageTableLib last year, can this be used instead? take care, Gerd -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#98777): https://edk2.groups.io/g/devel/message/98777 Mute This Topic: https://groups.io/mt/96045489/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
