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A !CONFIG_PV build or > > when running with FRED support will not populate the LSTAR/CSTAR stubs at > > CPU bringup. If a CPU is then offlined, the stubs page will be freed as > > its content will be all 0xcc, regardless of the stubs page still begin > > referenced by other CPUs. > > > > The new approach uses a global, CPU-indexed dynamically allocated array of > > stub addresses. However, to handle NUMA aware allocations, we cannot > > allocate all the memory in advance because of the NUMA dependency. Take > > advantage of the fact that Xen will attempt to contiguously pack CPUs on > > the same NUMA node (see normalise_cpu_order()), and on CPU bringup use the > > same stubs page the previous CPU did if suitable. Note the code would > > still function properly even if CPUs from NUMA nodes are not contiguously > > packed, it just consumes more memory. > > > > stub pages are no longer freed. They remain referenced in the global > > Nit: Didn't you mean to s/stub/Stub/ as per Andrew's comment? Hm, yes, I've fixed the instance below, but not the one here. > > CPU-indexed array and are re-used if the CPU is re-onlined. > > > > The stubs array doesn't have an explicit lock. During boot it's accessed > > single threaded. During runtime, &cpu_add_remove_lock serializes access. > > > > Fixes: 7a66ac8d1633 ("x86: move syscall trampolines off the stack") > > Signed-off-by: Jason Andryuk > > Signed-off-by: Roger Pau Monné > > Tested-by: Jason Andryuk > > Reviewed-by: Jason Andryuk > > Reviewed-by: Jan Beulich Thanks. I will run a CI pre-commit loop and push it today if it's all fine. Roger.