In the vcpu_run path the kernel may notice that a #vmexit is
necessary when preemption is already disabled. In the SVM
code an emulation of #vmexit may sleep and can't be executed
with preemtion disabled. This patch begins to solve this
problem by defining a KVM_REQ_VMEXIT bit. When this bit is
set the vcpu_run loop is restarted and a #vmexit is
emulated.
Signed-off-by: Joerg Roedel <joerg.roedel@xxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/x86.c | 17 +++++++++++++++++
include/linux/kvm_host.h | 1 +
3 files changed, 19 insertions(+), 0 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 179a919..50e5aa4 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -524,6 +524,7 @@ struct kvm_x86_ops {
int (*get_tdp_level)(void);
u64 (*get_mt_mask)(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio);
bool (*gb_page_enable)(void);
+ void (*emulate_vmexit)(struct kvm_vcpu *vcpu);
const struct trace_print_flags *exit_reasons_str;
};
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 11a6f2f..97e1d9d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3610,6 +3610,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
r = 0;
goto out;
}
+ if (test_and_clear_bit(KVM_REQ_VMEXIT, &vcpu->requests))
+ kvm_x86_ops->emulate_vmexit(vcpu);
}
preempt_disable();
@@ -3638,6 +3640,21 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
else if (kvm_cpu_has_interrupt(vcpu) || req_int_win)
kvm_x86_ops->enable_irq_window(vcpu);
+ /*
+ * With nested KVM the enable_irq_window() function may cause an
+ * #vmexit if the vcpu is running in guest mode. A #vmexit may sleep
+ * and can't be executed at this stage. So we use the request field to
+ * tell KVM that a #vmexit has to be done before we can enter the guest
+ * again. The code below checks for this request.
+ */
+ if (vcpu->requests) {
+ local_irq_enable();
+ preempt_enable();
+ r = 1;
+ goto out;
+ }
+
+
if (kvm_lapic_enabled(vcpu)) {
update_cr8_intercept(vcpu);
kvm_lapic_sync_to_vapic(vcpu);
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index b985a29..245463f 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -38,6 +38,7 @@
#define KVM_REQ_MMU_SYNC 7
#define KVM_REQ_KVMCLOCK_UPDATE 8
#define KVM_REQ_KICK 9
+#define KVM_REQ_VMEXIT 10
#define KVM_USERSPACE_IRQ_SOURCE_ID 0
--
1.6.4.3
--
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