Messages in this thread | | | Subject | Re: [PATCH 3/5] KVM: VMX: RTIT_CTL_BRANCH_EN has no dependency on other CPUID bit | From | Xiaoyao Li <> | Date | Wed, 25 Aug 2021 14:33:25 +0800 |
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On 8/25/2021 2:08 PM, Like Xu wrote: > On 25/8/2021 12:19 pm, Xiaoyao Li wrote: >> On 8/25/2021 11:30 AM, Like Xu wrote: >>> +Alexander >>> >>> On 24/8/2021 7:07 pm, Xiaoyao Li wrote: >>>> Per Intel SDM, RTIT_CTL_BRANCH_EN bit has no dependency on any CPUID >>>> leaf 0x14. >>>> >>>> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com> >>>> --- >>>> arch/x86/kvm/vmx/vmx.c | 8 ++++---- >>>> 1 file changed, 4 insertions(+), 4 deletions(-) >>>> >>>> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c >>>> index 7ed96c460661..4a70a6d2f442 100644 >>>> --- a/arch/x86/kvm/vmx/vmx.c >>>> +++ b/arch/x86/kvm/vmx/vmx.c >>>> @@ -7116,7 +7116,8 @@ static void update_intel_pt_cfg(struct >>>> kvm_vcpu *vcpu) >>>> /* Initialize and clear the no dependency bits */ >>>> vmx->pt_desc.ctl_bitmask = ~(RTIT_CTL_TRACEEN | RTIT_CTL_OS | >>>> - RTIT_CTL_USR | RTIT_CTL_TSC_EN | RTIT_CTL_DISRETC); >>>> + RTIT_CTL_USR | RTIT_CTL_TSC_EN | RTIT_CTL_DISRETC | >>>> + RTIT_CTL_BRANCH_EN); >>>> /* >>>> * If CPUID.(EAX=14H,ECX=0):EBX[0]=1 CR3Filter can be set >>>> otherwise >>>> @@ -7134,12 +7135,11 @@ static void update_intel_pt_cfg(struct >>>> kvm_vcpu *vcpu) >>>> RTIT_CTL_CYC_THRESH | RTIT_CTL_PSB_FREQ); >>>> /* >>>> - * If CPUID.(EAX=14H,ECX=0):EBX[3]=1 MTCEn BranchEn and >>>> - * MTCFreq can be set >>>> + * If CPUID.(EAX=14H,ECX=0):EBX[3]=1 MTCEn and MTCFreq can be set >>> >>> If CPUID.(EAX=14H,ECX=0):EBX[3]=1, >>> >>> "indicates support of MTC timing packet and suppression of >>> COFI-based packets." >> >> I think it's a mistake of SDM in CPUID instruction. >> >> If you read 31.3.1, table 31-11 of SDM 325462-075US, >> >> It just says CPUID(0x14, 0):EBX[3]: MTC supprted. >> It doesn't talk anything about COFI packets suppression. >> >> Further as below. >> >>> Per 31.2.5.4 Branch Enable (BranchEn), >>> >>> "If BranchEn is not set, then relevant COFI packets (TNT, TIP*, >>> FUP, MODE.*) are suppressed." >>> >>> I think if the COFI capability is suppressed, the software can't set >>> the BranchEn bit, right ? >> >> Based on your understanding, isn't it that >> >> 1. if CPUID.(EAX=14H,ECX=0):EBX[3]=0, it doesn't support "suppression >> of COFI-based packets". >> 2. if it doesn't support "suppression of COFI-based packets", then it >> doens't support "If BranchEn is not set, then relevant COFI packets >> (TNT, TIP*, FUP, MODE.*) are suppressed", i.e. BranchEn must be 1. > > That's it. > >> >> Anyway, I think it's just a mistake on CPUID instruction document of SDM. > > Is this an ambiguity rather than a mistake ? > >> >> CPUD.(EAX=14H,ECX=0):EBX[3] should only indicates the MTC support. > > Please do not make assertions that you do not confirm with hw. > >> >> BranchEn should be always supported if PT is available. Per "31.2.7.2 > > Check d35869ba348d3f1ff3e6d8214fe0f674bb0e404e.
This commit shows BranchEn is supported on BDW, and must be enabled on BDW. This doesn't conflict the description above that BranchEn should be always supported.
>> IA32_RTIT_CTL MSR" on SDM: >> When BranchEn is 1, it enables COFI-based packets. >> When BranchEn is 0, it disables COFI-based packtes. i.e., COFI packets >> are suppressed. >> >>>> */ >>>> if (intel_pt_validate_cap(vmx->pt_desc.caps, PT_CAP_mtc)) >>>> vmx->pt_desc.ctl_bitmask &= ~(RTIT_CTL_MTC_EN | >>>> - RTIT_CTL_BRANCH_EN | RTIT_CTL_MTC_RANGE); >>>> + RTIT_CTL_MTC_RANGE); >>>> /* If CPUID.(EAX=14H,ECX=0):EBX[4]=1 FUPonPTW and PTWEn can be >>>> set */ >>>> if (intel_pt_validate_cap(vmx->pt_desc.caps, PT_CAP_ptwrite)) >>>> >>
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