Il 30/08/2013 11:37, Laszlo Ersek ha scritto: > Disclaimer: I don't know what I'm talking about.
No problem. :) > So, Jordan's patch for OVMF (SVN r14494) builds the page tables (and > finally writes the root to CR3) in a phase when paging is not enabled > yet in the VM. > > Again, I have no clue, but if the guest hasn't even enabled paging yet, > then the hypervisor (without EPT?) might have no idea that what the > guest is writing to memory are its pagetables-to-be. The first notice > the hypervisor might take is the store to CR3. At which point (or maybe > even later, when paging is enabled?) the hypervisor would have to walk > the guest's tables all at once, and build the shadow tables "in batch". The hypervisor builds shadow page tables lazily; as soon as CR0.PG is set the next instruction will pagefault and shadow page tables will start to get populated. However, surprise! There is another set of "flat" page tables for X64, built by UefiCpuPkg/ResetVector/Vtf0/Tools/FixupForRawSection.py when you run UefiCpuPkg/ResetVector/Vtf0/Build.py. These are always in ROM. As in Jordan's patches, the problem is that the hypervisor is expecting to be able to write to the page tables, but this is not the case because the page tables are in a read-only memory slot. Making shadow and EPT behave similarly is probably a good thing, so I'm sending an RFC patch to k...@vger.kernel.org that fixes the bug. However, if you guys can figure out a patch for UefiCpuPkg/ResetVector/Vtf0/Ia32/Flat32ToFlat64.asm so that it builds the page tables in RAM (and removing the page table Python code), that would also work. Paolo ------------------------------------------------------------------------------ Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more! Discover the easy way to master current and previous Microsoft technologies and advance your career. Get an incredible 1,500+ hours of step-by-step tutorial videos with LearnDevNow. Subscribe today and save! http://pubads.g.doubleclick.net/gampad/clk?id=58040911&iu=/4140/ostg.clktrk _______________________________________________ edk2-devel mailing list edk2-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/edk2-devel
