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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2 4/4] x86/HVM: prefill cache with PDPTEs when possible
>>> On 14.09.18 at 04:18, <kevin.tian@xxxxxxxxx> wrote: >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx] >> Sent: Thursday, September 13, 2018 4:55 PM >> >> >>> On 13.09.18 at 08:30, <kevin.tian@xxxxxxxxx> wrote: >> >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx] >> >> Sent: Tuesday, September 11, 2018 9:16 PM >> >> >> >> Since strictly speaking it is incorrect for guest_walk_tables() to read >> >> L3 entries during PAE page walks, try to overcome this where possible by >> > >> > can you elaborate? why it's incorrect to read L3 entries? >> >> Architectural behavior: In PAE mode they get read upon CR3 loads, >> not during page walks. > > ah yes. can you add "CR3 load" in description which reminds > people easily? Extended text: Since strictly speaking it is incorrect for guest_walk_tables() to read L3 entries during PAE page walks (they get loaded from memory only upon CR3 loads and certain TLB flushes), try to overcome this where possible by pre-loading the values from hardware into the cache. Sadly the information is available in the EPT case only. On the positive side for NPT the spec spells out that L3 entries are actually read on walks, so us reading them is consistent with hardware behavior in that case. >> >> pre-loading the values from hardware into the cache. Sadly the >> >> information is available in the EPT case only. On the positive side for >> >> NPT the spec spells out that L3 entries are actually read on walks, so >> >> us reading them is consistent with hardware behavior in that case. >> > >> > I'm a little bit confused about the description here. you change >> > VMX code but using NPT spec as the reference? >> >> I'm trying to explain why there not being a way to do the same on >> NPT is not only not a problem, but in line with hardware behavior. >> > > Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx> Thanks. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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