Il 30/08/2013 14:10, Gleb Natapov ha scritto: > On Fri, Aug 30, 2013 at 01:58:59PM +0200, Paolo Bonzini wrote: >> 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. >> > Only when setting dirty/accessed bits, are they not set in ROM version > of page tables?
They are set, but the hypervisor is using gfn_to_hva unconditionally. See the patch I just posted. 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
