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From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>,
	"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
	Nitesh Narayan Lal <nitesh@redhat.com>,
	linux-kernel@vger.kernel.org
Subject: [PATCH v2 2/4] KVM: Guard cpusmask NULL check with CONFIG_CPUMASK_OFFSTACK
Date: Mon, 23 Aug 2021 16:30:26 +0200	[thread overview]
Message-ID: <20210823143028.649818-3-vkuznets@redhat.com> (raw)
In-Reply-To: <20210823143028.649818-1-vkuznets@redhat.com>

From: Sean Christopherson <seanjc@google.com>

Check for a NULL cpumask_var_t when kicking multiple vCPUs if and only if
cpumasks are configured to be allocated off-stack.  This is a meaningless
optimization, e.g. avoids a TEST+Jcc and TEST+CMOV on x86, but more
importantly helps document that the NULL check is necessary even though
all callers pass in a local variable.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 virt/kvm/kvm_main.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 786b914db98f..82c5280dd5ce 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -247,7 +247,7 @@ static void ack_flush(void *_completed)
 
 static inline bool kvm_kick_many_cpus(const struct cpumask *cpus, bool wait)
 {
-	if (unlikely(!cpus))
+	if (IS_ENABLED(CONFIG_CPUMASK_OFFSTACK) && unlikely(!cpus))
 		cpus = cpu_online_mask;
 
 	if (cpumask_empty(cpus))
@@ -277,6 +277,14 @@ bool kvm_make_vcpus_request_mask(struct kvm *kvm, unsigned int req,
 		if (!(req & KVM_REQUEST_NO_WAKEUP) && kvm_vcpu_wake_up(vcpu))
 			continue;
 
+		/*
+		 * tmp can be NULL if cpumasks are allocated off stack, as
+		 * allocation of the mask is deliberately not fatal and is
+		 * handled by falling back to kicking all online CPUs.
+		 */
+		if (IS_ENABLED(CONFIG_CPUMASK_OFFSTACK) && !tmp)
+			continue;
+
 		/*
 		 * Note, the vCPU could get migrated to a different pCPU at any
 		 * point after kvm_request_needs_ipi(), which could result in
@@ -288,7 +296,7 @@ bool kvm_make_vcpus_request_mask(struct kvm *kvm, unsigned int req,
 		 * were reading SPTEs _before_ any changes were finalized.  See
 		 * kvm_vcpu_kick() for more details on handling requests.
 		 */
-		if (tmp != NULL && kvm_request_needs_ipi(vcpu, req)) {
+		if (kvm_request_needs_ipi(vcpu, req)) {
 			cpu = READ_ONCE(vcpu->cpu);
 			if (cpu != -1 && cpu != me)
 				__cpumask_set_cpu(cpu, tmp);
-- 
2.31.1


  parent reply	other threads:[~2021-08-23 14:31 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-23 14:30 [PATCH v2 0/4] KVM: Various fixes and improvements around kicking vCPUs Vitaly Kuznetsov
2021-08-23 14:30 ` [PATCH v2 1/4] KVM: Clean up benign vcpu->cpu data races when " Vitaly Kuznetsov
2021-08-23 14:30 ` Vitaly Kuznetsov [this message]
2021-08-23 14:30 ` [PATCH v2 3/4] KVM: Optimize kvm_make_vcpus_request_mask() a bit Vitaly Kuznetsov
2021-08-23 14:30 ` [PATCH v2 4/4] KVM: x86: Fix stack-out-of-bounds memory access from ioapic_write_indirect() Vitaly Kuznetsov
2021-08-23 18:58   ` Eduardo Habkost
2021-08-24  7:13     ` Vitaly Kuznetsov
2021-08-24 14:23       ` Eduardo Habkost
2021-08-24 14:42         ` Vitaly Kuznetsov
2021-08-24 16:07           ` Maxim Levitsky
2021-08-24 17:40             ` Sean Christopherson
2021-08-25  8:26               ` Vitaly Kuznetsov
2021-08-25  8:21             ` Vitaly Kuznetsov
2021-08-25  9:11               ` Maxim Levitsky
2021-08-25  9:43                 ` Vitaly Kuznetsov
2021-08-25 10:41                   ` Maxim Levitsky
2021-08-25 13:19                   ` Eduardo Habkost
2021-08-26 12:40                     ` Vitaly Kuznetsov
2021-08-26 14:52                       ` Eduardo Habkost
2021-08-26 18:01                         ` Sean Christopherson
2021-08-26 18:13                           ` Eduardo Habkost
2021-08-26 19:27             ` Eduardo Habkost
2021-08-30 19:47             ` Nitesh Lal

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