On 10/18/18 4:20 PM, George Dunlap wrote: > On 10/12/2018 03:19 PM, Jan Beulich wrote: >>>>> On 12.10.18 at 15:55, <andrew.coop...@citrix.com> wrote: >>> On 11/09/18 14:10, Jan Beulich wrote: >>>> Emulation requiring device model assistance uses a form of instruction >>>> re-execution, assuming that the second (and any further) pass takes >>>> exactly the same path. This is a valid assumption as far as use of CPU >>>> registers goes (as those can't change without any other instruction >>>> executing in between), but is wrong for memory accesses. In particular >>>> it has been observed that Windows might page out buffers underneath >>>> an instruction currently under emulation (hitting between two passes). >>>> If the first pass translated a linear address successfully, any subsequent >>>> pass needs to do so too, yielding the exact same translation. >>>> >>>> Introduce a cache (used just by guest page table accesses for now, i.e. >>>> a form of "paging structure cache") to make sure above described >>>> assumption holds. This is a very simplistic implementation for now: Only >>>> exact matches are satisfied (no overlaps or partial reads or anything). >>>> >>>> There's also some seemingly unrelated cleanup here which was found >>>> desirable on the way. >>>> >>>> 1: x86/mm: add optional cache to GLA->GFN translation >>>> 2: x86/mm: use optional cache in guest_walk_tables() >>>> 3: x86/HVM: implement memory read caching >>>> 4: x86/HVM: prefill cache with PDPTEs when possible >>>> >>>> "VMX: correct PDPTE load checks" is omitted from v2, as I can't >>>> currently find enough time to carry out the requested further >>>> rework. >>> >>> Following the x86 call, I've had some thoughts and suggestions about how >>> to make this work in a reasonable way, without resorting to the full >>> caching approach. >> >> Thanks, but one question before I start thinking about this in >> more detail: Before writing this, did you read my mail from the >> 11th? I ask because what you suggest does not look to match >> the behavior I've described there as what I think it ought to be. > > I'm taking this off my to-review queue for now then -- let me know if > you need me to review it anyway.
BTW I'm now deleting this from my inbox to avoid clutter. Jan, at such time as you want me to review it, please ping or re-send. -George _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
