From: Sean Christopherson Date: Fri, 10 Nov 2023 02:28:57 +0000 (-0800) Subject: KVM: x86/pmu: Avoid CPL lookup if PMC enabline for USER and KERNEL is the same X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=83bdfe04c968e0fe3181e4cd41b764e17ac73911;p=linux.git KVM: x86/pmu: Avoid CPL lookup if PMC enabline for USER and KERNEL is the same Don't bother querying the CPL if a PMC is (not) counting for both USER and KERNEL, i.e. if the end result is guaranteed to be the same regardless of the CPL. Querying the CPL on Intel requires a VMREAD, i.e. isn't free, and a single CMP+Jcc is cheap. Link: https://lore.kernel.org/r/20231110022857.1273836-11-seanjc@google.com Signed-off-by: Sean Christopherson --- diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c index 8d81f176ab7be..c397b28e3d1b6 100644 --- a/arch/x86/kvm/pmu.c +++ b/arch/x86/kvm/pmu.c @@ -838,6 +838,13 @@ static inline bool cpl_is_matched(struct kvm_pmc *pmc) select_user = config & 0x2; } + /* + * Skip the CPL lookup, which isn't free on Intel, if the result will + * be the same regardless of the CPL. + */ + if (select_os == select_user) + return select_os; + return (static_call(kvm_x86_get_cpl)(pmc->vcpu) == 0) ? select_os : select_user; }