[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v3] x86/PV: remove unnecessary toggle_guest_pt() overhead
On 05/05/2020 07:16, Jan Beulich wrote: > While the mere updating of ->pv_cr3 and ->root_pgt_changed aren't overly > expensive (but still needed only for the toggle_guest_mode() path), the > effect of the latter on the exit-to-guest path is not insignificant. > Move the logic into toggle_guest_mode(), on the basis that > toggle_guest_pt() will always be invoked in pairs, yet we can't safely > undo the setting of root_pgt_changed during the second of these > invocations. > > While at it, add a comment ahead of toggle_guest_pt() to clarify its > intended usage. > > Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx> I'm still of the opinion that the commit message wants rewriting to get the important points across clearly. And those are that toggle_guest_pt() is called in pairs specifically to read kernel data structures when emulating a userspace action, and that this doesn't modify cr3 from the guests point of view, and therefore doesn't need the resync on exit-to-guest path. ~Andrew
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