On Thu, 11 Sep 2014, Leon Romanovsky wrote:
> > Linux kernel memory is not page-able, but memory allocated through vmalloc
> > can still cause page fault. How device drivers using vmalloc handle this?
> Pages allocated via vmalloc call won't generate page-faults.
Kernel faults are used on some platforms in a very limited way but not
for swapping in or "paging in from disk". Have a look at
linux/arch/x86/mm/fault.c:
/*
* We fault-in kernel-space virtual memory on-demand. The
* 'reference' page table is init_mm.pgd.
*
* NOTE! We MUST NOT take any locks for this case. We may
* be in an interrupt or a critical region, and should
* only copy the information from the master page table,
* nothing more.
*
* This verifies that the fault happens in kernel space
* (error_code & 4) == 0, and that the fault was not a
* protection error (error_code & 9) == 0.
*/
if (unlikely(fault_in_kernel_space(address))) {
if (!(error_code & (PF_RSVD | PF_USER | PF_PROT))) {
if (vmalloc_fault(address) >= 0)
return;
if (kmemcheck_fault(regs, address, error_code))
return;
}
/* Can handle a stale RO->RW TLB: */
if (spurious_fault(error_code, address))
return;
/* kprobes don't want to hook the spurious faults: */
if (kprobes_fault(regs))
return;
/*
* Don't take the mm semaphore here. If we fixup a prefetch
* fault we could otherwise deadlock:
*/
bad_area_nosemaphore(regs, error_code, address);
return;
}
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