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SubjectRe: [patch -mm 1/2] i386: add ptep_test_and_clear_{dirty,young}
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_*?


> 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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