http://bugzilla.opensuse.org/show_bug.cgi?id=1174374 http://bugzilla.opensuse.org/show_bug.cgi?id=1174374#c10 --- Comment #10 from Liang Yan <lyan@suse.com> --- Did a further research, the default of cap-ccf-assist is off but changed by below commit in qemu-5.0. =============== commit 37965dfe4dffa3ac49438337417608e7f346b58a Author: David Gibson <david@gibson.dropbear.id.au> Date: Thu Jan 30 10:28:56 2020 +1100 spapr: Enable DD2.3 accelerated count cache flush in pseries-5.0 machine For POWER9 DD2.2 cpus, the best current Spectre v2 indirect branch mitigation is "count cache disabled", which is configured with: -machine cap-ibs=fixed-ccd However, this option isn't available on DD2.3 CPUs with KVM, because they don't have the count cache disabled. + uint8_t kvm_ibs = kvmppc_get_cap_safe_indirect_branch(); + + if (kvm_ibs == SPAPR_CAP_FIXED_CCD) { + /* + * If we don't have CCF assist on the host, the assist + * instruction is a harmless no-op. It won't correctly + * implement the cache count flush *but* if we have + * count-cache-disabled in the host, that flush is + * unnnecessary. So, specifically allow this case. This + * allows us to have better performance on POWER9 DD2.3, + * while still working on POWER9 DD2.2 and POWER8 host + * cpus. + */ + return; + } error_setg(errp, "Requested count cache flush assist capability level not supported by kvm," " try appending -machine cap-ccf-assist=off"); } According to above code, it seems KVM host does not support count-cache-disabled. Because cap-ccf-assist will be recongnized as a no-op if it supports. You may need to update host firmware to support it. -- You are receiving this mail because: You are on the CC list for the bug.