Re: [PATCH 2/3] KVM: x86: Register Processor Trace interrupt hook iff PT enabled in guest

[Like Xu <like.xu.linux@gmail.com>]

On 24/8/2021 3:37 am, Sean Christopherson wrote:
> Override the Processor Trace (PT) interrupt handler for guest mode if and
> only if PT is configured for host+guest mode, i.e. is being used
> independently by both host and guest.  If PT is configured for system
> mode, the host fully controls PT and must handle all events.
> 
> Fixes: 8479e04e7d6b ("KVM: x86: Inject PMI for KVM guest")
> Cc: stable@vger.kernel.org
> Reported-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> Reported-by: Artem Kashkanov <artem.kashkanov@intel.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>   arch/x86/include/asm/kvm_host.h | 1 +
>   arch/x86/kvm/pmu.h              | 1 +
>   arch/x86/kvm/vmx/vmx.c          | 1 +
>   arch/x86/kvm/x86.c              | 4 +++-
>   4 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 09b256db394a..1ea4943a73d7 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1494,6 +1494,7 @@ struct kvm_x86_init_ops {
>   	int (*disabled_by_bios)(void);
>   	int (*check_processor_compatibility)(void);
>   	int (*hardware_setup)(void);
> +	bool (*intel_pt_intr_in_guest)(void);
>   
>   	struct kvm_x86_ops *runtime_ops;
>   };
> diff --git a/arch/x86/kvm/pmu.h b/arch/x86/kvm/pmu.h
> index 0e4f2b1fa9fb..b06dbbd7eeeb 100644
> --- a/arch/x86/kvm/pmu.h
> +++ b/arch/x86/kvm/pmu.h
> @@ -41,6 +41,7 @@ struct kvm_pmu_ops {
>   	void (*reset)(struct kvm_vcpu *vcpu);
>   	void (*deliver_pmi)(struct kvm_vcpu *vcpu);
>   	void (*cleanup)(struct kvm_vcpu *vcpu);
> +	void (*handle_intel_pt_intr)(void);
>   };
>   
>   static inline u64 pmc_bitmask(struct kvm_pmc *pmc)
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index fada1055f325..f19d72136f77 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7896,6 +7896,7 @@ static struct kvm_x86_init_ops vmx_init_ops __initdata = {
>   	.disabled_by_bios = vmx_disabled_by_bios,
>   	.check_processor_compatibility = vmx_check_processor_compat,
>   	.hardware_setup = hardware_setup,
> +	.intel_pt_intr_in_guest = vmx_pt_mode_is_host_guest,
>   
>   	.runtime_ops = &vmx_x86_ops,
>   };
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index fb6015f97f9e..b5ade47dad9c 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8305,7 +8305,7 @@ static struct perf_guest_info_callbacks kvm_guest_cbs = {
>   	.is_in_guest		= kvm_is_in_guest,
>   	.is_user_mode		= kvm_is_user_mode,
>   	.get_guest_ip		= kvm_get_guest_ip,
> -	.handle_intel_pt_intr	= kvm_handle_intel_pt_intr,
> +	.handle_intel_pt_intr	= NULL,
>   };
>   
>   #ifdef CONFIG_X86_64
> @@ -11061,6 +11061,8 @@ int kvm_arch_hardware_setup(void *opaque)
>   	memcpy(&kvm_x86_ops, ops->runtime_ops, sizeof(kvm_x86_ops));
>   	kvm_ops_static_call_update();
>   
> +	if (ops->intel_pt_intr_in_guest && ops->intel_pt_intr_in_guest())
> +		kvm_guest_cbs.handle_intel_pt_intr = kvm_handle_intel_pt_intr;

Emm, it's still buggy.

The guest "unknown NMI" from the host Intel PT can still be reproduced
after the following operation:

	rmmod kvm_intel
	modprobe kvm-intel pt_mode=1 ept=1
	rmmod kvm_intel
	modprobe kvm-intel pt_mode=1 ept=0

Since the handle_intel_pt_intr is not reset to NULL in kvm_arch_hardware_unsetup(),
and the previous function pointer still exists in the generic KVM data structure.

But I have to say that this fix is much better than the one I proposed [1].

[1] https://lore.kernel.org/lkml/20210514084436.848396-1-like.xu@linux.intel.com/

>   	perf_register_guest_info_callbacks(&kvm_guest_cbs);
>   
>   	if (!kvm_cpu_cap_has(X86_FEATURE_XSAVES))
>