Re: [Xen-devel] Page fault on mapped pages with reserved bits set

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 20/6/07 22:59, "Trammell Hudson" <hudson@xxxxxxxxxxxxxx> wrote:

> I can't handle the page fault, since my kernel's page fault routine
> faults if it tries to do anything that writes to memory, such as
> push a return address on the stack.  To generate the error message
> above I had to disable my kernel's trap table to let Xen handle it.
> Otherwise the fault address is in my handler rather than in the
> instruction after setting MMUEXT_BASE_PTR.
> 
> Any suggestions on things to try?

It's a protection violation on a write, because none of your page directory
entries have bit 1 (_PAGE_RW) set. That bit gets ANDed down the entire page
walk, so it needs to be set at every level for the page to actually be
writable.

 -- Keir



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