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Re: [Xen-devel] page table question!
hiI try to read the paging part code of xen-3.1.0, and I am confused about the " compat_machine_to_phys_mapping" ,what does xen do with the "CONFIG_COMPAT",and what are the differences between the "machine_to_phys_mapping" and the "compat_machine_to_phys_mapping"?
Could you help me Thanks in advance Petersson, Mats åé:
-----Original Message-----From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of MT RezaieSent: 13 June 2007 15:55 To: xen-devel@xxxxxxxxxxxxxxxxxxx Subject: [Xen-devel] page table question! I want to know any difference between writing, reading and shadow page table (for example performance).Not sure exactly what you're asking for: are you asking about "writable" and "non-writable" page-table vs. shadow-page-table? I believe "writable" page-table means that the guest is able to write DIRECTLY to the lower level(s) of the page-table, and as such, we "trust" the guest to do this correctly (and not map in stuff that doesn't belong to the guest). I believe this mode isn't normally used by Xen guests. This mode relies on the guest to correctly translate theguest-physical address to a machine physical address.Non-writable page-tables are mapped "read-only" throughout the entire page-table, and when a write occurs, the page-table is updated via the emulation of the instruction in the hypervisor. The hypervisor can checkthat the machine physical address is correct for the particular guest.As of currently, Shadow-mode is only used for HVM (fully virtualized) domains. In this case, the guest has a "dummy" page-table that is not used by the processor for any memory accesses, instead a "shadow" (copy) of the guest's page-table is used. The shadow page-table is used by the processor. To make updates to the page-table appear in the shadow-page-table, the hypervisor is making sure that the guest-page-table is read-only, and when the guest writes to the page-table, we reproduce the write [with modification to reflect the difference between guest physical and machine physical address]. -- MatsI am thankful for any help or resource for that. -- Best Regards Mohamad Taghi Mir Mohamad Rezaie Iran University of Science and Technology Department of Computer Science & Engineering System Software Group _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel_______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel .
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