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From: Sean Christopherson <seanjc@google.com>
To: Like Xu <like.xu.linux@gmail.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Mark Rutland <mark.rutland@arm.com>, Jiri Olsa <jolsa@redhat.com>,
	Namhyung Kim <namhyung@kernel.org>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, Artem Kashkanov <artem.kashkanov@intel.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 2/3] KVM: x86: Register Processor Trace interrupt hook iff PT enabled in guest
Date: Wed, 25 Aug 2021 14:59:57 +0000	[thread overview]
Message-ID: <YSZa7dkw6t7yN6vL@google.com> (raw)
In-Reply-To: <3021c1cc-a4eb-e3ab-d6b7-558cbaefd03b@gmail.com>

On Wed, Aug 25, 2021, Like Xu wrote:
> On 24/8/2021 3:37 am, Sean Christopherson wrote:
> > @@ -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.

Ooof, good catch.  Any preference between nullifying handle_intel_pt_intr in
setup() vs. unsetup()?  I think I like the idea of "unwinding" during unsetup(),
even though it splits the logic a bit.

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b5ade47dad9c..ffc6c2d73508 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11093,6 +11093,7 @@ int kvm_arch_hardware_setup(void *opaque)
 void kvm_arch_hardware_unsetup(void)
 {
        perf_unregister_guest_info_callbacks(&kvm_guest_cbs);
+       kvm_guest_cbs.handle_intel_pt_intr = NULL;

        static_call(kvm_x86_hardware_unsetup)();
 }


vs.


diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b5ade47dad9c..462aa7a360e9 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11063,6 +11063,8 @@ int kvm_arch_hardware_setup(void *opaque)

        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;
+       else
+               kvm_guest_cbs.handle_intel_pt_intr = NULL;
        perf_register_guest_info_callbacks(&kvm_guest_cbs);

        if (!kvm_cpu_cap_has(X86_FEATURE_XSAVES))

> 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))
> > 

  reply	other threads:[~2021-08-25 15:00 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-23 19:37 [PATCH 0/3] perf/x86/intel: KVM: PT intr handler fix and cleanup Sean Christopherson
2021-08-23 19:37 ` [PATCH 1/3] KVM: x86: Register perf callbacks after calling vendor's hardware_setup() Sean Christopherson
2021-08-23 19:37 ` [PATCH 2/3] KVM: x86: Register Processor Trace interrupt hook iff PT enabled in guest Sean Christopherson
2021-08-24  7:28   ` Alexander Shishkin
2021-08-24 14:11     ` Sean Christopherson
2021-08-25  7:24   ` Like Xu
2021-08-25 14:59     ` Sean Christopherson [this message]
2021-08-25 20:09       ` Sean Christopherson
2021-08-23 19:37 ` [PATCH 3/3] perf/x86/intel: Fold current_vcpu check into KVM's PT intr handler Sean Christopherson

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