On Mon, Sep 02, 2013 at 06:00:08PM +0200, Paolo Bonzini wrote: > 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). > They do it for a good reason, dirty bit exists only on the bottom level :) -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
