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From:   Andrea Arcangeli <aarcange@redhat.com>
To:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>
Subject: [PATCH 13/13] x86: retpolines: eliminate retpoline from msr event handlers
Date:   Mon,  4 Nov 2019 18:00:01 -0500
Message-Id: <20191104230001.27774-14-aarcange@redhat.com>
In-Reply-To: <20191104230001.27774-1-aarcange@redhat.com>
References: <20191104230001.27774-1-aarcange@redhat.com>
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It's enough to check the value and issue the direct call.

After this commit is applied, here the most common retpolines executed
under a high resolution timer workload in the guest on a VMX host:

[..]
@[
    trace_retpoline+1
    __trace_retpoline+30
    __x86_indirect_thunk_rax+33
    do_syscall_64+89
    entry_SYSCALL_64_after_hwframe+68
]: 267
@[]: 2256
@[
    trace_retpoline+1
    __trace_retpoline+30
    __x86_indirect_thunk_rax+33
    __kvm_wait_lapic_expire+284
    vmx_vcpu_run.part.97+1091
    vcpu_enter_guest+377
    kvm_arch_vcpu_ioctl_run+261
    kvm_vcpu_ioctl+559
    do_vfs_ioctl+164
    ksys_ioctl+96
    __x64_sys_ioctl+22
    do_syscall_64+89
    entry_SYSCALL_64_after_hwframe+68
]: 2390
@[]: 33410

@total: 315707

Note the highest hit above is __delay so probably not worth optimizing
even if it would be more frequent than 2k hits per sec.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---
 arch/x86/events/intel/core.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index fcef678c3423..937363b803c1 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -3323,8 +3323,19 @@ static int intel_pmu_hw_config(struct perf_event *ev=
ent)
 =09return 0;
 }
=20
+#ifdef CONFIG_RETPOLINE
+static struct perf_guest_switch_msr *core_guest_get_msrs(int *nr);
+static struct perf_guest_switch_msr *intel_guest_get_msrs(int *nr);
+#endif
+
 struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr)
 {
+#ifdef CONFIG_RETPOLINE
+=09if (x86_pmu.guest_get_msrs =3D=3D intel_guest_get_msrs)
+=09=09return intel_guest_get_msrs(nr);
+=09else if (x86_pmu.guest_get_msrs =3D=3D core_guest_get_msrs)
+=09=09return core_guest_get_msrs(nr);
+#endif
 =09if (x86_pmu.guest_get_msrs)
 =09=09return x86_pmu.guest_get_msrs(nr);
 =09*nr =3D 0;