[Xen-devel] Adding PTE Flag during Page Fault

[Joe Laws <jlaws@xxxxxxxxxxxxxx>]

I altered the method, "__spurious_page_fault", in "xen/arch/x86/traps.c"
to change a page to present when it is marked as not present.  I am
attempting to do this using the "l1e_add_flags(l1e, _PAGE_PRESENT);" 
definition call.  I then set it to return EXCRET_fault_fixed, so the
trap should have the client retry what it was doing with the changes I
made.  Unfortunately after it returns from the page fault to the user,
it immediately faults again on the same error at the same memory
location.  This means my "l1e_add_flags(l1e, _PAGE_PRESENT)" is not
actually updating the correct location in memory or  if it is, the
changes get discarded immediately.  Does anyone who is familiar with the
page_fault trap code have any idea why my change to the PTE is not
sticking.  I tried doing a TLB flush for the memory address, but the
same thing happens.  My only other guess is that the l1e defined in the
function is just a copy of the actual table entry, so I need to look
back further where l1e was defined.

Thanks,
Joe


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