On Mon, Jul 12, 2021 at 06:10:30PM +0800, Like Xu wrote: > On 12/7/2021 5:36 pm, Yang Weijiang wrote: > >On Fri, Jul 09, 2021 at 02:55:35PM -0700, Jim Mattson wrote: > >>On Fri, Jul 9, 2021 at 2:51 AM Yang Weijiang <weijiang.yang@xxxxxxxxx> wrote: > >>> > >>>From: Like Xu <like.xu@xxxxxxxxxxxxxxx> > >>> > >>>Arch LBRs are enabled by setting MSR_ARCH_LBR_CTL.LBREn to 1. A new guest > >>>state field named "Guest IA32_LBR_CTL" is added to enhance guest LBR usage. > >>>When guest Arch LBR is enabled, a guest LBR event will be created like the > >>>model-specific LBR does. Clear guest LBR enable bit on host PMI handling so > >>>guest can see expected config. > >>> > >>>On processors that support Arch LBR, MSR_IA32_DEBUGCTLMSR[bit 0] has no > >>>meaning. It can be written to 0 or 1, but reads will always return 0. > >>>Like IA32_DEBUGCTL, IA32_ARCH_LBR_CTL msr is also reserved on INIT. > >> > >>I suspect you mean "preserved" rather than "reserved." > >Yes, should be preserved. > > > >> > >>>Signed-off-by: Like Xu <like.xu@xxxxxxxxxxxxxxx> > >>>Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx> > >>>--- > >>> arch/x86/events/intel/lbr.c | 2 -- > >>> arch/x86/include/asm/msr-index.h | 1 + > >>> arch/x86/include/asm/vmx.h | 2 ++ > >>> arch/x86/kvm/vmx/pmu_intel.c | 31 ++++++++++++++++++++++++++----- > >>> arch/x86/kvm/vmx/vmx.c | 9 +++++++++ > >>> 5 files changed, 38 insertions(+), 7 deletions(-) > >>> > >> > >>>diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c > >>>index da68f0e74702..4500c564c63a 100644 > >>>--- a/arch/x86/kvm/vmx/pmu_intel.c > >>>+++ b/arch/x86/kvm/vmx/pmu_intel.c > >>>@@ -19,6 +19,11 @@ > >>> #include "pmu.h" > >>> > >>> #define MSR_PMC_FULL_WIDTH_BIT (MSR_IA32_PMC0 - MSR_IA32_PERFCTR0) > >>>+/* > >>>+ * Regardless of the Arch LBR or legacy LBR, when the LBR_EN bit 0 of the > >>>+ * corresponding control MSR is set to 1, LBR recording will be enabled. > >>>+ */ > >> > >>Is this comment misplaced? It doesn't seem to have anything to do with > >>the macro being defined below. > >Agree, will put this in commit message. > >> > >>>@@ -458,6 +467,14 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > >>> lbr_desc->records.nr = data; > >>> lbr_desc->arch_lbr_reset = true; > >>> return 0; > >>>+ case MSR_ARCH_LBR_CTL: > >>>+ if (data & ~KVM_ARCH_LBR_CTL_MASK) > >> > >>Is a static mask sufficient? Per the Intel® Architecture Instruction > >>Set Extensions and Future Features Programming Reference, some of > >>these bits may not be supported on all microarchitectures. See Table > >>7-8. CPUID Leaf 01CH Enumeration of Architectural LBR Capabilities. > >Yes, more sanity checks are required, thanks! > > > >> > >>>+ break; > >>>+ vmcs_write64(GUEST_IA32_LBR_CTL, data); > >>>+ if (intel_pmu_lbr_is_enabled(vcpu) && !lbr_desc->event && > >>>+ (data & ARCH_LBR_CTL_LBREN)) > >>>+ intel_pmu_create_guest_lbr_event(vcpu); > >> > >>Nothing has to be done when the LBREN bit goes from 1 to 0? > >Need to release the event and reset related flag when the bit goes from > >1 to 0. Thanks! > > No need to release the LBR event and it will be lazily released. > I forgot the lazy cleanup :-), thanks! > >> > >>>+ return 0; > >>> default: > >>> if ((pmc = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0)) || > >>> (pmc = get_gp_pmc(pmu, msr, MSR_IA32_PMC0))) { > >> > >>Per the Intel® Architecture Instruction Set Extensions and Future > >>Features Programming Reference, "IA32_LBR_CTL.LBREn is saved and > >>cleared on #SMI, and restored on RSM." I don't see that happening > >>anywhere. That manual also says, "On a warm reset...IA32_LBR_CTL.LBREn > >>is cleared to 0, disabling LBRs." I don't see that happening either. > > > >Yes, I'll add related code to make it consistent with spec, thanks! > >> > >>I have a question about section 7.1.4.4 in that manual. It says, "On a > >>debug breakpoint event (#DB), IA32_LBR_CTL.LBREn is cleared." When, > >>exactly, does that happen? In particular, if kvm synthesizes such an > >>event (for example, in kvm_vcpu_do_singlestep), does > >>IA32_LBR_CTL.LBREn automatically get cleared (after loading the guest > >>IA32_LBR_CTL value from the VMCS)? Or does kvm need to explicitly > >>clear that bit in the VMCS before injecting the #DB? > >OK, I don't have answer now, will ask the Arch to get clear answer on this, > >thanks for raising the question! > > I think we also need a kvm-unit-tests to cover it (as well as the legacy > LBR). > Yes, I'll add one later. > >