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Date: Tue, 18 May 2021 15:38:52 +0800
From: "Xu, Like" <like.xu@...el.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
Borislav Petkov <bp@...en8.de>,
Sean Christopherson <seanjc@...gle.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>, weijiang.yang@...el.com,
Kan Liang <kan.liang@...ux.intel.com>, ak@...ux.intel.com,
wei.w.wang@...el.com, eranian@...gle.com, liuxiangdong5@...wei.com,
linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org,
Like Xu <like.xu@...ux.intel.com>
Subject: Re: [PATCH v6 02/16] perf/x86/intel: Handle guest PEBS overflow PMI
for KVM guest
On 2021/5/17 16:16, Peter Zijlstra wrote:
> On Tue, May 11, 2021 at 10:42:00AM +0800, Like Xu wrote:
>> With PEBS virtualization, the guest PEBS records get delivered to the
>> guest DS, and the host pmi handler uses perf_guest_cbs->is_in_guest()
>> to distinguish whether the PMI comes from the guest code like Intel PT.
>>
>> No matter how many guest PEBS counters are overflowed, only triggering
>> one fake event is enough. The fake event causes the KVM PMI callback to
>> be called, thereby injecting the PEBS overflow PMI into the guest.
>>
>> KVM may inject the PMI with BUFFER_OVF set, even if the guest DS is
>> empty. That should really be harmless. Thus guest PEBS handler would
>> retrieve the correct information from its own PEBS records buffer.
>>
>> Originally-by: Andi Kleen <ak@...ux.intel.com>
>> Co-developed-by: Kan Liang <kan.liang@...ux.intel.com>
>> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
>> Signed-off-by: Like Xu <like.xu@...ux.intel.com>
>> ---
>> arch/x86/events/intel/core.c | 40 ++++++++++++++++++++++++++++++++++++
>> 1 file changed, 40 insertions(+)
>>
>> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
>> index b6e45ee10e16..092ecacf8345 100644
>> --- a/arch/x86/events/intel/core.c
>> +++ b/arch/x86/events/intel/core.c
>> @@ -2780,6 +2780,43 @@ static void intel_pmu_reset(void)
>> local_irq_restore(flags);
>> }
>>
>> +/*
>> + * We may be running with guest PEBS events created by KVM, and the
>> + * PEBS records are logged into the guest's DS and invisible to host.
>> + *
>> + * In the case of guest PEBS overflow, we only trigger a fake event
>> + * to emulate the PEBS overflow PMI for guest PBES counters in KVM.
>> + * The guest will then vm-entry and check the guest DS area to read
>> + * the guest PEBS records.
>> + *
>> + * The contents and other behavior of the guest event do not matter.
>> + */
>> +static void x86_pmu_handle_guest_pebs(struct pt_regs *regs,
>> + struct perf_sample_data *data)
>> +{
>> + struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
>> + u64 guest_pebs_idxs = cpuc->pebs_enabled & ~cpuc->intel_ctrl_host_mask;
>> + struct perf_event *event = NULL;
>> + int bit;
>> +
>> + if (!x86_pmu.pebs_active || !guest_pebs_idxs)
>> + return;
>> +
>> + for_each_set_bit(bit, (unsigned long *)&guest_pebs_idxs,
>> + INTEL_PMC_IDX_FIXED + x86_pmu.num_counters_fixed) {
>> + event = cpuc->events[bit];
>> + if (!event->attr.precise_ip)
>> + continue;
>> +
>> + perf_sample_data_init(data, 0, event->hw.last_period);
>> + if (perf_event_overflow(event, data, regs))
>> + x86_pmu_stop(event, 0);
>> +
>> + /* Inject one fake event is enough. */
>> + break;
>> + }
>> +}
>> +
>> static int handle_pmi_common(struct pt_regs *regs, u64 status)
>> {
>> struct perf_sample_data data;
>> @@ -2831,6 +2868,9 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status)
>> u64 pebs_enabled = cpuc->pebs_enabled;
>>
>> handled++;
>> + if (x86_pmu.pebs_vmx && perf_guest_cbs &&
>> + perf_guest_cbs->is_in_guest())
>> + x86_pmu_handle_guest_pebs(regs, &data);
>> x86_pmu.drain_pebs(regs, &data);
>> status &= intel_ctrl | GLOBAL_STATUS_TRACE_TOPAPMI;
>>
> I'm thinking you have your conditions in the wrong order; would it not
> be much cheaper to first check: '!x86_pmu.pebs_active || !guest_pebs_idx'
> than to do that horrible indirect ->is_in_guest() call?
>
> After all, if the guest doesn't have PEBS enabled, who cares if we're
> currently in a guest or not.
Yes, it makes sense. How about:
@@ -2833,6 +2867,10 @@ static int handle_pmi_common(struct pt_regs *regs,
u64 status)
u64 pebs_enabled = cpuc->pebs_enabled;
handled++;
+ if (x86_pmu.pebs_vmx && x86_pmu.pebs_active &&
+ (cpuc->pebs_enabled & ~cpuc->intel_ctrl_host_mask) &&
+ (static_call(x86_guest_state)() & PERF_GUEST_ACTIVE))
+ x86_pmu_handle_guest_pebs(regs, &data);
x86_pmu.drain_pebs(regs, &data);
status &= intel_ctrl | GLOBAL_STATUS_TRACE_TOPAPMI;
>
> Also, something like the below perhaps (arm64 and xen need fixing up at
> the very least) could make all that perf_guest_cbs stuff suck less.
How about the commit message for your below patch:
From: "Peter Zijlstra (Intel)" <peterz@...radead.org>
x86/core: Use static_call to rewrite perf_guest_info_callbacks
The two fields named "is_in_guest" and "is_user_mode" in
perf_guest_info_callbacks are replaced with a new multiplexed member
named "state", and the "get_guest_ip" field will be renamed to "get_ip".
The application of DEFINE_STATIC_CALL_RET0 (arm64 and xen need fixing
up at the very least) could make all that perf_guest_cbs stuff suck less.
For KVM, these callbacks will be updated in the kvm_arch_init().
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
----
I'm not sue if you have a strong reason to violate the check-patch rule:
ERROR: Using weak declarations can have unintended link defects
#238: FILE: include/linux/perf_event.h:1242:
+extern void __weak arch_perf_update_guest_cbs(void);
?
>
> ---
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index 8e509325c2c3..c8f8fb7c0536 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -90,6 +90,26 @@ DEFINE_STATIC_CALL_NULL(x86_pmu_pebs_aliases, *x86_pmu.pebs_aliases);
> */
> DEFINE_STATIC_CALL_RET0(x86_pmu_guest_get_msrs, *x86_pmu.guest_get_msrs);
>
> +DEFINE_STATIC_CALL_RET0(x86_guest_state, *(perf_guest_cbs->state));
> +DEFINE_STATIC_CALL_RET0(x86_guest_get_ip, *(perf_guest_cbs->get_ip));
> +DEFINE_STATIC_CALL_RET0(x86_guest_handle_intel_pt_intr, *(perf_guest_cbs->handle_intel_pt_intr));
> +
> +void arch_perf_update_guest_cbs(void)
> +{
> + static_call_update(x86_guest_state, (void *)&__static_call_return0);
> + static_call_update(x86_guest_get_ip, (void *)&__static_call_return0);
> + static_call_update(x86_guest_handle_intel_pt_intr, (void *)&__static_call_return0);
> +
> + if (perf_guest_cbs && perf_guest_cbs->state)
> + static_call_update(x86_guest_state, perf_guest_cbs->state);
> +
> + if (perf_guest_cbs && perf_guest_cbs->get_ip)
> + static_call_update(x86_guest_get_ip, perf_guest_cbs->get_ip);
> +
> + if (perf_guest_cbs && perf_guest_cbs->handle_intel_pt_intr)
> + static_call_update(x86_guest_handle_intel_pt_intr, perf_guest_cbs->handle_intel_pt_intr);
> +}
> +
> u64 __read_mostly hw_cache_event_ids
> [PERF_COUNT_HW_CACHE_MAX]
> [PERF_COUNT_HW_CACHE_OP_MAX]
> @@ -2736,7 +2756,7 @@ perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *re
> struct unwind_state state;
> unsigned long addr;
>
> - if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) {
> + if (static_call(x86_guest_state)()) {
> /* TODO: We don't support guest os callchain now */
> return;
> }
> @@ -2839,7 +2859,7 @@ perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs
> struct stack_frame frame;
> const struct stack_frame __user *fp;
>
> - if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) {
> + if (static_call(x86_guest_state)()) {
> /* TODO: We don't support guest os callchain now */
> return;
> }
> @@ -2916,18 +2936,21 @@ static unsigned long code_segment_base(struct pt_regs *regs)
>
> unsigned long perf_instruction_pointer(struct pt_regs *regs)
> {
> - if (perf_guest_cbs && perf_guest_cbs->is_in_guest())
> - return perf_guest_cbs->get_guest_ip();
> + unsigned long ip = static_call(x86_guest_get_ip)();
> +
> + if (likely(!ip))
> + ip = regs->ip + code_segment_base(regs);
>
> - return regs->ip + code_segment_base(regs);
> + return ip;
> }
>
> unsigned long perf_misc_flags(struct pt_regs *regs)
> {
> + unsigned int guest = static_call(x86_guest_state)();
> int misc = 0;
>
> - if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) {
> - if (perf_guest_cbs->is_user_mode())
> + if (guest) {
> + if (guest & PERF_GUEST_USER)
> misc |= PERF_RECORD_MISC_GUEST_USER;
> else
> misc |= PERF_RECORD_MISC_GUEST_KERNEL;
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index 2521d03de5e0..ac422c45f940 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -2780,6 +2780,8 @@ static void intel_pmu_reset(void)
> local_irq_restore(flags);
> }
>
> +DECLARE_STATIC_CALL(x86_guest_handle_intel_pt_intr, *(perf_guest_cbs->handle_intel_pt_intr));
> +
> static int handle_pmi_common(struct pt_regs *regs, u64 status)
> {
> struct perf_sample_data data;
> @@ -2850,10 +2852,7 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status)
> */
> if (__test_and_clear_bit(GLOBAL_STATUS_TRACE_TOPAPMI_BIT, (unsigned long *)&status)) {
> handled++;
> - if (unlikely(perf_guest_cbs && perf_guest_cbs->is_in_guest() &&
> - perf_guest_cbs->handle_intel_pt_intr))
> - perf_guest_cbs->handle_intel_pt_intr();
> - else
> + if (!static_call(x86_guest_handle_intel_pt_intr)())
> intel_pt_interrupt();
> }
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 55efbacfc244..2a24e615fa4a 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1812,7 +1812,7 @@ int kvm_skip_emulated_instruction(struct kvm_vcpu *vcpu);
> int kvm_complete_insn_gp(struct kvm_vcpu *vcpu, int err);
> void __kvm_request_immediate_exit(struct kvm_vcpu *vcpu);
>
> -int kvm_is_in_guest(void);
> +unsigned int kvm_guest_state(void);
>
> void __user *__x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa,
> u32 size);
> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> index 827886c12c16..2dcbd1b30004 100644
> --- a/arch/x86/kvm/pmu.c
> +++ b/arch/x86/kvm/pmu.c
> @@ -87,7 +87,7 @@ static void kvm_perf_overflow_intr(struct perf_event *perf_event,
> * woken up. So we should wake it, but this is impossible from
> * NMI context. Do it from irq work instead.
> */
> - if (!kvm_is_in_guest())
> + if (!kvm_guest_state())
> irq_work_queue(&pmc_to_pmu(pmc)->irq_work);
> else
> kvm_make_request(KVM_REQ_PMI, pmc->vcpu);
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index bbc4e04e67ad..88f709b3759c 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8035,44 +8035,46 @@ static void kvm_timer_init(void)
> DEFINE_PER_CPU(struct kvm_vcpu *, current_vcpu);
> EXPORT_PER_CPU_SYMBOL_GPL(current_vcpu);
>
> -int kvm_is_in_guest(void)
> +static unsigned int kvm_guest_state(void)
> {
> - return __this_cpu_read(current_vcpu) != NULL;
> -}
> -
> -static int kvm_is_user_mode(void)
> -{
> - int user_mode = 3;
> + struct kvm_vcpu *vcpu = __this_cpu_read(current_vcpu);
> + unsigned int state = 0;
>
> - if (__this_cpu_read(current_vcpu))
> - user_mode = static_call(kvm_x86_get_cpl)(__this_cpu_read(current_vcpu));
> + if (vcpu)
> + state |= PERF_GUEST_ACTIVE;
> + if (static_call(kvm_x86_get_cpl)(vcpu))
> + state |= PERF_GUEST_USER;
>
> - return user_mode != 0;
> + return state;
> }
>
> -static unsigned long kvm_get_guest_ip(void)
> +static unsigned long kvm_guest_get_ip(void)
> {
> + struct kvm_vcpu *vcpu = __this_cpu_read(current_vcpu);
> unsigned long ip = 0;
>
> - if (__this_cpu_read(current_vcpu))
> - ip = kvm_rip_read(__this_cpu_read(current_vcpu));
> + if (vcpu)
> + ip = kvm_rip_read(vcpu);
>
> return ip;
> }
>
> -static void kvm_handle_intel_pt_intr(void)
> +static unsigned int kvm_handle_intel_pt_intr(void)
> {
> struct kvm_vcpu *vcpu = __this_cpu_read(current_vcpu);
>
> + if (!vcpu)
> + return 0;
> +
> kvm_make_request(KVM_REQ_PMI, vcpu);
> __set_bit(MSR_CORE_PERF_GLOBAL_OVF_CTRL_TRACE_TOPA_PMI_BIT,
> (unsigned long *)&vcpu->arch.pmu.global_status);
> + return 1;
> }
>
> 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,
> + .state = kvm_guest_state,
> + .get_ip = kvm_guest_get_ip,
> .handle_intel_pt_intr = kvm_handle_intel_pt_intr,
> };
>
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index f5a6a2f069ed..7eae1fd22db3 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -26,11 +26,13 @@
> # include <asm/local64.h>
> #endif
>
> +#define PERF_GUEST_ACTIVE 0x01
> +#define PERF_GUEST_USER 0x02
> +
> struct perf_guest_info_callbacks {
> - int (*is_in_guest)(void);
> - int (*is_user_mode)(void);
> - unsigned long (*get_guest_ip)(void);
> - void (*handle_intel_pt_intr)(void);
> + unsigned int (*state)(void);
> + unsigned long (*get_ip)(void);
> + unsigned int (*handle_intel_pt_intr)(void);
> };
>
> #ifdef CONFIG_HAVE_HW_BREAKPOINT
> @@ -1237,6 +1239,8 @@ extern void perf_event_bpf_event(struct bpf_prog *prog,
> u16 flags);
>
> extern struct perf_guest_info_callbacks *perf_guest_cbs;
> +extern void __weak arch_perf_update_guest_cbs(void);
> +
> extern int perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *callbacks);
> extern int perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *callbacks);
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 2e947a485898..aec531fc9c90 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -6486,9 +6486,17 @@ static void perf_pending_event(struct irq_work *entry)
> */
> struct perf_guest_info_callbacks *perf_guest_cbs;
>
> +void __weak arch_perf_update_guest_cbs(void)
> +{
> +}
> +
> int perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
> {
> + if (WARN_ON_ONCE(perf_guest_cbs))
> + return -EBUSY;
> +
> perf_guest_cbs = cbs;
> + arch_perf_update_guest_cbs();
> return 0;
> }
> EXPORT_SYMBOL_GPL(perf_register_guest_info_callbacks);
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