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@xxxxxxxxx>
---
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.
Anyway, I think it's just a mistake on CPUID instruction document of SDM.
CPUD.(EAX=14H,ECX=0):EBX[3] should only indicates the MTC support.
BranchEn should be always supported if PT is available. Per "31.2.7.2
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))
