KVM: x86/pmu: Always stuff GuestOnly=1,HostOnly=0 for mediated PMCs on AMD

On AMD platforms, there is no way to restore PerfCntrGlobalCtl at
VM-Entry or clear it at VM-Exit. Since the register states will be
restored before entering and saved after exiting guest context, the
counters can keep ticking and even overflow leading to chaos while
still in host context.

To avoid this, intecept event selectors, which is already done by mediated
PMU. In addition, always set the GuestOnly bit and clear the HostOnly bit
for PMU selectors on AMD. Doing so allows the counters run only in guest
context even if their enable bits are still set after VM exit and before
host/guest PMU context switch.

Signed-off-by: Sandipan Das <sandipan.das@amd.com>
Signed-off-by: Mingwei Zhang <mizhang@google.com>
[sean: massage shortlog]
Tested-by: Xudong Hao <xudong.hao@intel.com>
Tested-by: Manali Shukla <manali.shukla@amd.com>
Link: https://patch.msgid.link/20251206001720.468579-27-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
index c1ec1962314ec2406eea767bb5a76cd8f29bf6f7..6d5f791126b13d851b287a9add4e04bd8e45e989 100644 (file)
--- a/arch/x86/kvm/svm/pmu.c
+++ b/arch/x86/kvm/svm/pmu.c
@@ -166,7 +166,8 @@ static int amd_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
                data &= ~pmu->reserved_bits;
                if (data != pmc->eventsel) {
                        pmc->eventsel = data;
-                       pmc->eventsel_hw = data;
+                       pmc->eventsel_hw = (data & ~AMD64_EVENTSEL_HOSTONLY) |
+                                          AMD64_EVENTSEL_GUESTONLY;
                        kvm_pmu_request_counter_reprogram(pmc);
                }
                return 0;