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    SubjectRe: [RFC PATCH 0/2] KVM: VMX: Fix VM entry failure on PT_MODE_HOST_GUEST while host is using PT
    On Mon, Aug 29, 2022, Wang, Wei W wrote:
    > On Thursday, August 25, 2022 4:56 PM, Xiaoyao Li wrote:
    > #if defined(CONFIG_PERF_EVENTS) && defined(CONFIG_CPU_SUP_AMD)
    > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
    > index d7f8331d6f7e..195debc1bff1 100644
    > --- a/arch/x86/kvm/vmx/vmx.c
    > +++ b/arch/x86/kvm/vmx/vmx.c
    > @@ -1125,37 +1125,29 @@ static inline void pt_save_msr(struct pt_ctx *ctx, u32 addr_range)
    >
    > static void pt_guest_enter(struct vcpu_vmx *vmx)
    > {
    > - if (vmx_pt_mode_is_system())
    > + struct perf_event *event;
    > +
    > + if (vmx_pt_mode_is_system() ||
    > + !(vmx->pt_desc.guest.ctl & RTIT_CTL_TRACEEN))

    I don't think the host should trace the guest in the host/guest mode just because
    the guest isn't tracing itself. I.e. the host still needs to turn off it's own
    tracing.

    > return;
    >
    > - /*
    > - * GUEST_IA32_RTIT_CTL is already set in the VMCS.
    > - * Save host state before VM entry.
    > - */
    > - rdmsrl(MSR_IA32_RTIT_CTL, vmx->pt_desc.host.ctl);
    > - if (vmx->pt_desc.guest.ctl & RTIT_CTL_TRACEEN) {
    > - wrmsrl(MSR_IA32_RTIT_CTL, 0);
    > - pt_save_msr(&vmx->pt_desc.host, vmx->pt_desc.num_address_ranges);
    > - pt_load_msr(&vmx->pt_desc.guest, vmx->pt_desc.num_address_ranges);
    > - }
    > + event = pt_get_curr_event();
    > + perf_event_disable(event);
    > + vmx->pt_desc.host_event = event;

    This is effectively what I suggested[*], the main difference being that my version
    adds dedicated enter/exit helpers so that perf can skip save/restore of the other
    MSRs. It's easy to extend if perf needs to hand back an event to complete the "exit.

    bool guest_trace_enabled = vmx->pt_desc.guest.ctl & RTIT_CTL_TRACEEN;

    vmx->pt_desc.host_event = intel_pt_guest_enter(guest_trace_enabled);


    and then on exit

    bool guest_trace_enabled = vmx->pt_desc.guest.ctl & RTIT_CTL_TRACEEN;

    intel_pt_guest_exit(vmx->pt_desc.host_event, guest_trace_enabled);

    [*] https://lore.kernel.org/all/YwecducnM%2FU6tqJT@google.com

    > + pt_load_msr(&vmx->pt_desc.guest, vmx->pt_desc.num_address_ranges);
    > }

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