Simon Kagstrom wrote:

Hello!
I have some problems setting up a custom GDT (I need one where the
code is readable). Anyway, I try to switch to my own GDT as follows:
 unsigned long frames[16];
 volatile unsigned long va = (unsigned long)GDT;
 volatile unsigned long pa = to_phys(va);
 volatile unsigned long ma = phys_to_machine(pa) & ~_PAGE_RW | _PAGE_PRESENT 
| _PAGE_ACCESSED | _PAGE_DIRTY;
 /* Make it read-only */
 HYPERVISOR_update_va_mapping(va, (pte_t){ ma }, 0);
 frames[0] = ma;
 int ret = HYPERVISOR_set_gdt(frames, 16);
(The GDT Is just copied from Linux' right now). When doing this, I
always get -EINVAL from set_gdt, which I suspect is because
HYPERVISOR_update_va_mapping for some reason does not succeed in
setting the page read-only.
I've checked the Linux implementation, and it does basically the same
thing (pte_wrprotect() on the machine-address before calling
update_va_mapping). Does anyone see what is wrong here?
// Simon
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frames[0] = ma >> PAGE_SHIFT;
should fix you problem.
Mathieu
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