Zachary Amsden wrote:
I though about it, but it gets really ugly. You need wrappers for all
the MMU ops in pvops generic code, which means either another layer of
wrappers or a bunch of CONFIG_DEBUG_PARAVIRT
Oh, yes, more wrappers please! We could do it at the paravirt_ops
level: set up your pv_ops, then call paravirt_debug_mmuops(), which
would save away your ops and replace them with wrappers. That basic
structure would lend itself to all kinds of paravirt-level debugging tools.
It would be a bit more elegant if we had mmu_ops. Maybe we should do
that splitup before 64bit?
only things that are easy to break because they also depend on PAE vs.
non-PAE.
Hm, would they? Would they need to inspect the content of the pte_t
(etc), or just look at the struct page for the page being updated? (pmd
operations being a bit more awkward, of course.)
It's doable, though, and might even be extensible to s390 for CMM page
type debugging, as well as descriptor type tracking and enforcement of
page isolation of GDTs.
Page state tracking could track -
PAGE_ZERO, PAGE_UNUSED, PAGE_STABLE, PAGE_VOLATILE,
PAGE_POTENTIALLY_VOLATILE, PAGE_L1{2/3/4}, PAGE_LDT, PAGE_GDT,
actually, no this seems silly, since we'd just be duplicating bits for
the page types, so the only debug benefit is ensuring the intersection
of volatile and L{1/2/3/4} is nil, which is already trivially
verifiable by inspection.
Well, I have to say that keeping the hypervisor hints in sync with the
actual kernel-level page state worries me, so any debug tools which
could help there would be good. This seems like it should be the right
place to do it, but I can't say I've thought about it in any detail.
Of course, if it *is* helpful to the page hinting patches, then it
suggests that it's a facility with wider scope than pv-ops.
J
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