Il 02/09/2013 11:25, Gleb Natapov ha scritto: > On Mon, Sep 02, 2013 at 05:20:15PM +0800, Xiao Guangrong wrote: >> On 08/30/2013 08:41 PM, Paolo Bonzini wrote: >>> Page tables in a read-only memory slot will currently cause a triple >>> fault because the page walker uses gfn_to_hva and it fails on such a slot. >>> >>> OVMF uses such a page table; however, real hardware seems to be fine with >>> that as long as the accessed/dirty bits are set. Save whether the slot >>> is readonly, and later check it when updating the accessed and dirty bits. >> >> Paolo, do you know why OVMF is using readonly memory like this? >> > Just a guess, but perhaps they want to move to paging mode as early as > possible even before memory controller is fully initialized.
More precisely they want to move to 64-bit mode as early as possible, and that requires paging. >> AFAIK, The fault trigged by this kind of access can hardly be fixed by >> userspace since the fault is trigged by pagetable walking not by the current >> instruction. Do you have any idea to let uerspace emulate it properly? > > Not sure what userspace you mean here, but there shouldn't be a fault in the > first place if ROM page tables have access/dirty bit set and they do. Yep. Actually they do not set dirty on the PD/PDP/PML4, only on the bottom level (which is also fine). 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 [email protected] https://lists.sourceforge.net/lists/listinfo/edk2-devel
