Commit de0f6195 authored by Like Xu's avatar Like Xu Committed by Paolo Bonzini
Browse files

KVM: x86/pmu: Defer counter emulated overflow via pmc->prev_counter 



Defer reprogramming counters and handling overflow via KVM_REQ_PMU
when incrementing counters.  KVM skips emulated WRMSR in the VM-Exit
fastpath, the fastpath runs with IRQs disabled, skipping instructions
can increment and reprogram counters, reprogramming counters can
sleep, and sleeping is disallowed while IRQs are disabled.

 [*] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:580
 [*] in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 2981888, name: CPU 15/KVM
 [*] preempt_count: 1, expected: 0
 [*] RCU nest depth: 0, expected: 0
 [*] INFO: lockdep is turned off.
 [*] irq event stamp: 0
 [*] hardirqs last  enabled at (0): [<0000000000000000>] 0x0
 [*] hardirqs last disabled at (0): [<ffffffff8121222a>] copy_process+0x146a/0x62d0
 [*] softirqs last  enabled at (0): [<ffffffff81212269>] copy_process+0x14a9/0x62d0
 [*] softirqs last disabled at (0): [<0000000000000000>] 0x0
 [*] Preemption disabled at:
 [*] [<ffffffffc2063fc1>] vcpu_enter_guest+0x1001/0x3dc0 [kvm]
 [*] CPU: 17 PID: 2981888 Comm: CPU 15/KVM Kdump: 5.19.0-rc1-g239111db364c-dirty #2
 [*] Call Trace:
 [*]  <TASK>
 [*]  dump_stack_lvl+0x6c/0x9b
 [*]  __might_resched.cold+0x22e/0x297
 [*]  __mutex_lock+0xc0/0x23b0
 [*]  perf_event_ctx_lock_nested+0x18f/0x340
 [*]  perf_event_pause+0x1a/0x110
 [*]  reprogram_counter+0x2af/0x1490 [kvm]
 [*]  kvm_pmu_trigger_event+0x429/0x950 [kvm]
 [*]  kvm_skip_emulated_instruction+0x48/0x90 [kvm]
 [*]  handle_fastpath_set_msr_irqoff+0x349/0x3b0 [kvm]
 [*]  vmx_vcpu_run+0x268e/0x3b80 [kvm_intel]
 [*]  vcpu_enter_guest+0x1d22/0x3dc0 [kvm]

Add a field to kvm_pmc to track the previous counter value in order
to defer overflow detection to kvm_pmu_handle_event() (the counter must
be paused before handling overflow, and that may increment the counter).

Opportunistically shrink sizeof(struct kvm_pmc) a bit.

Suggested-by: default avatarWanpeng Li <wanpengli@tencent.com>
Fixes: 9cd803d4 ("KVM: x86: Update vPMCs when retiring instructions")
Signed-off-by: default avatarLike Xu <likexu@tencent.com>
Link: https://lore.kernel.org/r/20220831085328.45489-6-likexu@tencent.com


[sean: avoid re-triggering KVM_REQ_PMU on overflow, tweak changelog]
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20220923001355.3741194-5-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 68fb4757

arch/x86/include/asm/kvm_host.h

+3 −2
Original line number Diff line number Diff line
@@ -491,7 +491,10 @@ enum pmc_type { 
struct kvm_pmc {

	enum pmc_type type;

	u8 idx;

	bool is_paused;

	bool intr;

	u64 counter;

	u64 prev_counter;

	u64 eventsel;

	struct perf_event *perf_event;

	struct kvm_vcpu *vcpu;
@@ -501,8 +504,6 @@ struct kvm_pmc { 
	 * ctrl value for fixed counters.

	 */

	u64 current_config;

	bool is_paused;

	bool intr;

};



/* More counters may conflict with other existing Architectural MSRs */

arch/x86/kvm/pmu.c

+16 −16
Original line number Diff line number Diff line
@@ -101,14 +101,6 @@ static inline void __kvm_perf_overflow(struct kvm_pmc *pmc, bool in_pmi) 
	struct kvm_pmu *pmu = pmc_to_pmu(pmc);

	bool skip_pmi = false;



	/*

	 * Ignore overflow events for counters that are scheduled to be

	 * reprogrammed, e.g. if a PMI for the previous event races with KVM's

	 * handling of a related guest WRMSR.

	 */

	if (test_and_set_bit(pmc->idx, pmu->reprogram_pmi))

		return;



	if (pmc->perf_event && pmc->perf_event->attr.precise_ip) {

		if (!in_pmi) {

			/*
@@ -126,7 +118,6 @@ static inline void __kvm_perf_overflow(struct kvm_pmc *pmc, bool in_pmi) 
	} else {

		__set_bit(pmc->idx, (unsigned long *)&pmu->global_status);

	}

	kvm_make_request(KVM_REQ_PMU, pmc->vcpu);



	if (!pmc->intr || skip_pmi)

		return;
@@ -151,7 +142,17 @@ static void kvm_perf_overflow(struct perf_event *perf_event, 
{

	struct kvm_pmc *pmc = perf_event->overflow_handler_context;



	/*

	 * Ignore overflow events for counters that are scheduled to be

	 * reprogrammed, e.g. if a PMI for the previous event races with KVM's

	 * handling of a related guest WRMSR.

	 */

	if (test_and_set_bit(pmc->idx, pmc_to_pmu(pmc)->reprogram_pmi))

		return;



	__kvm_perf_overflow(pmc, true);



	kvm_make_request(KVM_REQ_PMU, pmc->vcpu);

}



static int pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type, u64 config,
@@ -311,6 +312,9 @@ static void reprogram_counter(struct kvm_pmc *pmc) 
	if (!check_pmu_event_filter(pmc))

		goto reprogram_complete;



	if (pmc->counter < pmc->prev_counter)

		__kvm_perf_overflow(pmc, false);



	if (eventsel & ARCH_PERFMON_EVENTSEL_PIN_CONTROL)

		printk_once("kvm pmu: pin control bit is ignored\n");
@@ -348,6 +352,7 @@ static void reprogram_counter(struct kvm_pmc *pmc) 


reprogram_complete:

	clear_bit(pmc->idx, (unsigned long *)&pmc_to_pmu(pmc)->reprogram_pmi);

	pmc->prev_counter = 0;

}



void kvm_pmu_handle_event(struct kvm_vcpu *vcpu)
@@ -536,14 +541,9 @@ void kvm_pmu_destroy(struct kvm_vcpu *vcpu) 


static void kvm_pmu_incr_counter(struct kvm_pmc *pmc)

{

	u64 prev_count;



	prev_count = pmc->counter;

	pmc->prev_counter = pmc->counter;

	pmc->counter = (pmc->counter + 1) & pmc_bitmask(pmc);



	reprogram_counter(pmc);

	if (pmc->counter < prev_count)

		__kvm_perf_overflow(pmc, false);

	kvm_pmu_request_counter_reprogam(pmc);

}



static inline bool eventsel_match_perf_hw_id(struct kvm_pmc *pmc,

arch/x86/kvm/svm/pmu.c

+1 −1
Original line number Diff line number Diff line
@@ -212,7 +212,7 @@ static void amd_pmu_reset(struct kvm_vcpu *vcpu) 
		struct kvm_pmc *pmc = &pmu->gp_counters[i];



		pmc_stop_counter(pmc);

		pmc->counter = pmc->eventsel = 0;

		pmc->counter = pmc->prev_counter = pmc->eventsel = 0;

	}

}

arch/x86/kvm/vmx/pmu_intel.c

+2 −2
Original line number Diff line number Diff line
@@ -646,14 +646,14 @@ static void intel_pmu_reset(struct kvm_vcpu *vcpu) 
		pmc = &pmu->gp_counters[i];



		pmc_stop_counter(pmc);

		pmc->counter = pmc->eventsel = 0;

		pmc->counter = pmc->prev_counter = pmc->eventsel = 0;

	}



	for (i = 0; i < KVM_PMC_MAX_FIXED; i++) {

		pmc = &pmu->fixed_counters[i];



		pmc_stop_counter(pmc);

		pmc->counter = 0;

		pmc->counter = pmc->prev_counter = 0;

	}



	pmu->fixed_ctr_ctrl = pmu->global_ctrl = pmu->global_status = 0;