Messages in this thread | | | Date | Thu, 18 Sep 2008 17:42:25 -0700 | From | Jeremy Fitzhardinge <> | Subject | Re: Populating multiple ptes at fault time |
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Avi Kivity wrote: >> >> The only direct use of pte_young() is in zap_pte_range, within a >> mmu_lazy region. So syncing the A bit state on entering lazy mmu mode >> would work fine there. >> >> > > Ugh, leaving lazy pte.a mode when entering lazy mmu mode?
Well, sort of but not quite. The kernel's announcing its about to start processing a batch of ptes, so the hypervisor can take the opportunity to update their state before processing. "Lazy-mode" is from the perspective of the kernel lazily updating some state the hypervisor might care about, and the sync happens when leaving mode.
The flip-side is when the hypervisor is lazily updating some state the kernel cares about, so it makes sense that the sync when the kernel enters its lazy mode. But the analogy isn't very good because we don't really have an explicit notion of "hypervisor lazy mode", or a formal handoff of shared state between the kernel and hypervisor. But in this case the behaviour isn't too bad.
>> The call via page_referenced_one() doesn't seem to have a very >> convenient hook though. Perhaps putting something in >> page_check_address() would do the job. >> >> > > Why there? > > Why not explicitly in the callers? We need more than to exit lazy > pte.a mode, we also need to enter it again later. >
Because that's the code that actually walks the pagetable and has the address of the pte; it just returns a pte_t, not a pte_t *. It depends on whether you want fetch the A bit via ptep or vaddr (in general we pass mm, ptep and vaddr to ops which operate on the current pagetable).
J
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