On 07/02/18 16:12, Jan Beulich wrote: > I'm not sure why I didn't do this right away: By avoiding the use of > global PTEs in the cloned directmap, there's no need to fiddle with > CR4.PGE on any of the entry paths. Only the exit paths need to flush > global mappings. > > The reduced flushing, however, implies that we now need to have > interrupts off on all entry paths until after the page table switch, so > that flush IPIs can't arrive with the restricted page tables still > active, but only a non-global flush happening with the CR3 loads. Along > those lines the "sync" IPI after L4 entry updates now needs to become a > real (and global) flush IPI, so that inside Xen we'll also pick up such > changes.
Actually, on second consideration, why does reenabling interrupts need to be deferred? The safety of the sync_guest path (which previously entered Xen, did nothing, and exited again) relied on the entry part flushing global mappings for safety, as the return-to-xen path doesn't necessarily switch mappings. However, the first hunk upgrading the "do nothing" to a proper global flush, covers that case. I don't see anything else which affects the safety of taking TLB flush IPIs early in the entry-from-guest path. What am I missing? ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
