tree e1be9c5e1571b82af6e2c7d4bc4e805fcd51627c
parent cc08ef1185c57a175878029e888b9665cd3bc730
author Colton Lewis <coltonlewis@google.com> 1675812776 +0000
committer Andrew Jones <andrew.jones@linux.dev> 1676402973 +0100

arm: Replace MAX_SMP probe loop in favor of reading directly

Replace the MAX_SMP probe loop in favor of reading a number directly
from the QEMU error message. This is equally safe as the existing code
because the error message has had the same format as long as it has
existed, since QEMU v2.10. The final number before the end of the
error message line indicates the max QEMU supports.

This loop logic is broken for machines with a number of CPUs that
isn't a power of two. This problem was noticed for gicv2 tests on
machines with a non-power-of-two number of CPUs greater than 8 because
tests were running with MAX_SMP less than 8. As a hypothetical example,
a machine with 12 CPUs will test with MAX_SMP=6 because 12 >> 1 ==
6. This can, in rare circumstances, lead to different test results
depending only on the number of CPUs the machine has.

A previous comment explains the loop should only apply to kernels
<=v4.3 on arm and suggests deletion when it becomes tiresome to
maintain. However, it is always theoretically possible to test on a
machine that has more CPUs than QEMU supports, so it makes sense to
leave some check in place.

Signed-off-by: Colton Lewis <coltonlewis@google.com>
Signed-off-by: Andrew Jones <andrew.jones@linux.dev>