lkml.org 
[lkml]   [2013]   [Sep]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] KVM: mmu: allow page tables to be in read-only slots
    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.


    \
     
     \ /
      Last update: 2013-09-02 11:41    [W:4.317 / U:0.312 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site