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authorLike Xu <likexu@tencent.com>2023-11-23 08:58:18 +0100
committerSean Christopherson <seanjc@google.com>2023-11-29 19:22:55 +0100
commit547c91929f437b42e6a9c90fec1fb5aec3e64aac (patch)
treefd454bd5ed25c86365e93ee72592d5ab044f820f /arch
parentLinux 6.6 (diff)
downloadlinux-547c91929f437b42e6a9c90fec1fb5aec3e64aac.tar.xz
linux-547c91929f437b42e6a9c90fec1fb5aec3e64aac.zip
KVM: x86: Get CPL directly when checking if loaded vCPU is in kernel mode
When querying whether or not a vCPU "is" running in kernel mode, directly get the CPL if the vCPU is the currently loaded vCPU. In scenarios where a guest is profiled via perf-kvm, querying vcpu->arch.preempted_in_kernel from kvm_guest_state() is wrong if vCPU is actively running, i.e. isn't scheduled out due to being preempted and so preempted_in_kernel is stale. This affects perf/core's ability to accurately tag guest RIP with PERF_RECORD_MISC_GUEST_{KERNEL|USER} and record it in the sample. This causes perf/tool to fail to connect the vCPU RIPs to the guest kernel space symbols when parsing these samples due to incorrect PERF_RECORD_MISC flags: Before (perf-report of a cpu-cycles sample): 1.23% :58945 [unknown] [u] 0xffffffff818012e0 After: 1.35% :60703 [kernel.vmlinux] [g] asm_exc_page_fault Note, checking preempted_in_kernel in kvm_arch_vcpu_in_kernel() is awful as nothing in the API's suggests that it's safe to use if and only if the vCPU was preempted. That can be cleaned up in the future, for now just fix the glaring correctness bug. Note #2, checking vcpu->preempted is NOT safe, as getting the CPL on VMX requires VMREAD, i.e. is correct if and only if the vCPU is loaded. If the target vCPU *was* preempted, then it can be scheduled back in after the check on vcpu->preempted in kvm_vcpu_on_spin(), i.e. KVM could end up trying to do VMREAD on a VMCS that isn't loaded on the current pCPU. Signed-off-by: Like Xu <likexu@tencent.com> Fixes: e1bfc24577cc ("KVM: Move x86's perf guest info callbacks to generic KVM") Link: https://lore.kernel.org/r/20231123075818.12521-1-likexu@tencent.com [sean: massage changelong, add Fixes] Signed-off-by: Sean Christopherson <seanjc@google.com>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kvm/x86.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 41cce5031126..3b6a0109191b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12910,7 +12910,10 @@ bool kvm_arch_vcpu_in_kernel(struct kvm_vcpu *vcpu)
if (vcpu->arch.guest_state_protected)
return true;
- return vcpu->arch.preempted_in_kernel;
+ if (vcpu != kvm_get_running_vcpu())
+ return vcpu->arch.preempted_in_kernel;
+
+ return static_call(kvm_x86_get_cpl)(vcpu) == 0;
}
unsigned long kvm_arch_vcpu_get_ip(struct kvm_vcpu *vcpu)