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Jason Andryuk
4f2c223c59
Today the inline tracking of the stub page is problematic. 0xcc is used to
indicate unused, but it is also a "clear value." 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.
Stubs pages are no longer freed. They remain referenced in the global
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: 7a66ac8d16 ("x86: move syscall trampolines off the stack")
Signed-off-by: Jason Andryuk <jason.andryuk@amd.com>
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Tested-by: Jason Andryuk <jason.andryuk@amd.com>
Reviewed-by: Jason Andryuk <jason.andryuk@amd.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>