Messages in this thread | | | Date | Mon, 2 Sep 2013 12:25:18 +0300 | From | Gleb Natapov <> | Subject | Re: [PATCH] KVM: mmu: allow page tables to be in read-only slots |
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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.
> 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.
-- Gleb.
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