[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH RFC v2 1/4] x86/mm: Shadow and p2m changes for PV mem_access
>> In the PV case step 2 is problematic as the range of pages that belong >> to the PV guest is unknown to the mem-access listener. I tried adding >> another PV specific API for setting default access that will walk the >> page_list and set the shadow_flag to default. But Jan rightly pointed >> out issues surrounding hypercall preemption / continuation during >> which, the page_list could be modified. So my current plan is to blow >> all shadow pages every time the API for setting default access is >> called. The on the subsequent page-faults where the PTE is marked not >> present, set the shadow_flag to the default access as part of creating >> the PTE. > >How do you know when this step finishes? I.e. how can you tell the >difference between an access field in the shadow_flags that was set before >you enabled mem_access and one that was set since? What I was thinking of doing is, in p2m_mem_access_get_entry(), check if PTE for the page is marked present and return the access value in the shadow_flags if it is. If it is not present, then return the default access value. >At some point you need some more state - either something resetting the >shadow_flags (though indeed I don't know how to do that reliably and safely) >or an epoch counter (which there isn't room for) or some other trick that I >can't think of right now. At the moment, I have some code in assign_pages() to reset the shadow_flags to the default value. So that will take care of resetting pages assigned to new domains. Thanks, Aravindh _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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