Re: [PATCH] Fix lazy mode vmalloc synchronization for paravirt

Zachary Amsden wrote:

Found this looping Ubuntu installs with VMI.

If unlucky enough to hit a vmalloc sync fault during a lazy mode
operation (from an IRQ handler for a module which was not yet
populated in current page directory, or from inside copy_one_pte,
which touches swap_map, and hit in an unused 4M region), the required
PDE update would never get flushed, causing an infinite page fault loop.

Ah, good catch.

This bug affects any paravirt-ops backend which uses lazy updates, I
believe that makes it a bug in Xen, VMI and lguest.  It only happens
on LOWMEM kernels. 

No, under Xen the kernel/hypervisor PMD is not shared between processes,
so this is still used when PAE is enabled.

    J