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ISA v2.06 adds new variations of wait, specified by the WC field. These are not all compatible with the prior wait implementation, because they add additional conditions that cause the processor to resume, which can cause software to hang or run very slowly. At this moment, with the current wait implementation and a pseries guest using mainline kernel with new wait upcodes [1], QEMU hangs during boot if more than one CPU is present: qemu-system-ppc64 -M pseries,x-vof=on -cpu POWER10 -smp 2 -nographic -kernel zImage.pseries -no-reboot QEMU will exit (as there's no filesystem) if the test "passes", or hang during boot if it hits the bug. ISA v3.0 changed the wait opcode and removed the new variants (retaining the WC field but making non-zero values reserved). ISA v3.1 added new WC values to the new wait opcode, and added a PL field. This patch implements the new wait encoding and supports WC variants with no-op implementations, which provides basic correctness as explained in comments. [1] https://lore.kernel.org/all/20220720132132.903462-1-npiggin@gmail.com/ Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Reviewed-by: Víctor Colombo <victor.colombo@eldorado.org.br> Tested-by: Joel Stanley <joel@jms.id.au> Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com> Message-Id: <20220720133352.904263-1-npiggin@gmail.com> [danielhb: added information about the bug being fixed] Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com> |
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