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author | Liran Alon <liran.alon@oracle.com> | 2017-11-09 20:27:20 +0200 |
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committer | Radim Krčmář <rkrcmar@redhat.com> | 2018-01-16 16:40:09 +0100 |
commit | 6b6977117f50d60455ace86b2d256f6fb4f3de05 (patch) | |
tree | b88e950fc6f5acff04802d2a28d2a06ab7540502 /arch/x86/kvm | |
parent | 851c1a18c5412fd321e387cfe60739387cdbf37d (diff) | |
download | op-kernel-dev-6b6977117f50d60455ace86b2d256f6fb4f3de05.zip op-kernel-dev-6b6977117f50d60455ace86b2d256f6fb4f3de05.tar.gz |
KVM: nVMX: Fix races when sending nested PI while dest enters/leaves L2
Consider the following scenario:
1. CPU A calls vmx_deliver_nested_posted_interrupt() to send an IPI
to CPU B via virtual posted-interrupt mechanism.
2. CPU B is currently executing L2 guest.
3. vmx_deliver_nested_posted_interrupt() calls
kvm_vcpu_trigger_posted_interrupt() which will note that
vcpu->mode == IN_GUEST_MODE.
4. Assume that before CPU A sends the physical POSTED_INTR_NESTED_VECTOR
IPI, CPU B exits from L2 to L0 during event-delivery
(valid IDT-vectoring-info).
5. CPU A now sends the physical IPI. The IPI is received in host and
it's handler (smp_kvm_posted_intr_nested_ipi()) does nothing.
6. Assume that before CPU A sets pi_pending=true and KVM_REQ_EVENT,
CPU B continues to run in L0 and reach vcpu_enter_guest(). As
KVM_REQ_EVENT is not set yet, vcpu_enter_guest() will continue and resume
L2 guest.
7. At this point, CPU A sets pi_pending=true and KVM_REQ_EVENT but
it's too late! CPU B already entered L2 and KVM_REQ_EVENT will only be
consumed at next L2 entry!
Another scenario to consider:
1. CPU A calls vmx_deliver_nested_posted_interrupt() to send an IPI
to CPU B via virtual posted-interrupt mechanism.
2. Assume that before CPU A calls kvm_vcpu_trigger_posted_interrupt(),
CPU B is at L0 and is about to resume into L2. Further assume that it is
in vcpu_enter_guest() after check for KVM_REQ_EVENT.
3. At this point, CPU A calls kvm_vcpu_trigger_posted_interrupt() which
will note that vcpu->mode != IN_GUEST_MODE. Therefore, do nothing and
return false. Then, will set pi_pending=true and KVM_REQ_EVENT.
4. Now CPU B continue and resumes into L2 guest without processing
the posted-interrupt until next L2 entry!
To fix both issues, we just need to change
vmx_deliver_nested_posted_interrupt() to set pi_pending=true and
KVM_REQ_EVENT before calling kvm_vcpu_trigger_posted_interrupt().
It will fix the first scenario by chaging step (6) to note that
KVM_REQ_EVENT and pi_pending=true and therefore process
nested posted-interrupt.
It will fix the second scenario by two possible ways:
1. If kvm_vcpu_trigger_posted_interrupt() is called while CPU B has changed
vcpu->mode to IN_GUEST_MODE, physical IPI will be sent and will be received
when CPU resumes into L2.
2. If kvm_vcpu_trigger_posted_interrupt() is called while CPU B hasn't yet
changed vcpu->mode to IN_GUEST_MODE, then after CPU B will change
vcpu->mode it will call kvm_request_pending() which will return true and
therefore force another round of vcpu_enter_guest() which will note that
KVM_REQ_EVENT and pi_pending=true and therefore process nested
posted-interrupt.
Cc: stable@vger.kernel.org
Fixes: 705699a13994 ("KVM: nVMX: Enable nested posted interrupt processing")
Signed-off-by: Liran Alon <liran.alon@oracle.com>
Reviewed-by: Nikita Leshenko <nikita.leshchenko@oracle.com>
Reviewed-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
[Add kvm_vcpu_kick to also handle the case where L1 doesn't intercept L2 HLT
and L2 executes HLT instruction. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Diffstat (limited to 'arch/x86/kvm')
-rw-r--r-- | arch/x86/kvm/vmx.c | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 2a96b1a..2c8749e 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -5146,14 +5146,15 @@ static int vmx_deliver_nested_posted_interrupt(struct kvm_vcpu *vcpu, if (is_guest_mode(vcpu) && vector == vmx->nested.posted_intr_nv) { - /* the PIR and ON have been set by L1. */ - kvm_vcpu_trigger_posted_interrupt(vcpu, true); /* * If a posted intr is not recognized by hardware, * we will accomplish it in the next vmentry. */ vmx->nested.pi_pending = true; kvm_make_request(KVM_REQ_EVENT, vcpu); + /* the PIR and ON have been set by L1. */ + if (!kvm_vcpu_trigger_posted_interrupt(vcpu, true)) + kvm_vcpu_kick(vcpu); return 0; } return -1; |