Messages in this thread | | | Date | Mon, 26 Mar 2007 12:20:21 -0800 | From | Zachary Amsden <> | Subject | Re: [patch -mm 1/2] i386: add ptep_test_and_clear_{dirty,young} |
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Hugh Dickins wrote: > On Sun, 25 Mar 2007, Zachary Amsden wrote: > >> If you actually clear the bit, you need to: >> >> + pte_update_defer(vma->vm_mm, addr, ptep); >> >> The reason is, when updating PTEs, the hypervisor must be notified. Using >> atomic operations to do this is fine for all hypervisors I am aware of. >> However, for hypervisors which shadow page tables, if these PTE modifications >> are not trapped, you need a post-modification call to fulfill the update of >> the shadow page table. >> > > Thanks for the very rapid response. > > So, David just needs to move the pte_update_defer out of > ptep_clear_flush_* and into ptep_test_and_clear_*? >
Yes.
> That leaves me wondering why you deleted ptep_test_and_clear_* > (while leaving their __HAVE_ARCHes) in the first place? >
Because raw use of them in the arch independent MM code would introduce exactly this bug on i386, so leaving __HAVE_ARCH but leaving out the definition would catch this case.
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