On Sun, Sep 15, 2019 at 11:28:13AM +1000, Nicholas Piggin wrote:

Add support for the scv instruction on POWER9 and later CPUs.

For now this implements the zeroth scv vector 'scv 0', as identical
to 'sc' system calls, with the exception that lr is not preserved, and
it is 64-bit only. There may yet be changes made to this ABI, so it's
for testing only.

This also doesn't yet properly handle PR KVM, or the case where a guest
is denied AIL=3 mode. I haven't added real mode entry points, so scv
must not be used when AIL=0, but I haven't cleared the FSCR in this
case.

This also implements a strange hack to handle the non-implemented
vectors, scheduling a decrementer and expecting it to interrupt and
replay pending soft masked interrupts. This is unlikely to be a good
idea, and needs to actually do a proper handler and replay in case an
interrupt is pending.

It may also require some errata handling before it can be safely used
on all POWER9 CPUs, I have to look that up.

rfscv is implemented to return from scv type system calls. It can not
be used to return from sc system calls because those are defined to
preserve lr.

In a comparison of getpid syscall, the test program had scv taking
about 3 more cycles in user mode (92 vs 89 for sc), due to lr handling.
Total cycles taken for a getpid system call on POWER9 are improved from
436 to 345 (26.3% faster), mostly due to reducing mtmsr and mtspr.

...

This adds another instance of the lack of endian conversion issue.

+			accumulate_stolen_time();
+	}
+#endif

Thanks

Michal