Messages in this thread | | | Subject | Re: [PATCH v3 00/17] KVM: x86/pmu: Add support to enable Guest PEBS via DS | From | "Xu, Like" <> | Date | Mon, 25 Jan 2021 20:53:27 +0800 |
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On 2021/1/25 20:18, Peter Zijlstra wrote: > On Mon, Jan 25, 2021 at 08:07:06PM +0800, Xu, Like wrote: > >> So under the premise that counter cross-mapping is allowed, >> how can hypercall help fix it ? > Hypercall or otherwise exposing the mapping, will let the guest fix it > up when it already touches the data. Which avoids the host from having > to access the guest memory and is faster, no? - as you may know, the mapping table is changing rapidly from the time records to be rewritten to the time records to be read;
- the patches will modify the records before it is notified via PMI which means it's transparent to normal guests (including Windows);
- a malicious guest would ignore the exposed mapping and the hypercall and I don't think it can solve the leakage issue at all;
- make the guest aware of that hypercall or mapping requires more code changes in the guest side; but now we can make it on the KVM side and we also know that cross-mapping case rarely happens, and the overhead is acceptable based on our tests;
Please let me know if you or Sean are not going to buy in the PEBS records rewrite proposal in the patch 13 - 17.
--- thx,likexu
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