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KVM: VMX: Do not change PID.NDST when loading a blocked vCPU 

When vCPU enters block phase, pi_pre_block() inserts vCPU to a per pCPU
linked list of all vCPUs that are blocked on this pCPU. Afterwards, it
changes PID.NV to POSTED_INTR_WAKEUP_VECTOR which its handler
(wakeup_handler()) is responsible to kick (unblock) any vCPU on that
linked list that now has pending posted interrupts.

While vCPU is blocked (in kvm_vcpu_block()), it may be preempted which
will cause vmx_vcpu_pi_put() to set PID.SN.  If later the vCPU will be
scheduled to run on a different pCPU, vmx_vcpu_pi_load() will clear
PID.SN but will also *overwrite PID.NDST to this different pCPU*.
Instead of keeping it with original pCPU which vCPU had entered block
phase on.

This results in an issue because when a posted interrupt is delivered, as
the wakeup_handler() will be executed and fail to find blocked vCPU on
its per pCPU linked list of all vCPUs that are blocked on this pCPU.
Which is due to the vCPU being placed on a *different* per pCPU
linked list i.e. the original pCPU in which it entered block phase.

The regression is introduced by commit c112b5f502 ("KVM: x86:
Recompute PID.ON when clearing PID.SN"). Therefore, partially revert
it and reintroduce the condition in vmx_vcpu_pi_load() responsible for
avoiding changing PID.NDST when loading a blocked vCPU.

Fixes: c112b5f502 ("KVM: x86: Recompute PID.ON when clearing PID.SN")
Tested-by: Nathan Ni <nathan.ni@oracle.com>
Co-developed-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Joao Martins 2019-11-11 17:20:11 +00:00 committed by Paolo Bonzini
parent 9482ae458b
commit 132194ffa1
2 changed files with 20 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
arch/x86/kvm/vmx/vmx.c
View File

@ -1268,6 +1268,18 @@ static void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)
if (!pi_test_sn(pi_desc) && vcpu->cpu == cpu)
return;
/*
* If the 'nv' field is POSTED_INTR_WAKEUP_VECTOR, do not change
* PI.NDST: pi_post_block is the one expected to change PID.NDST and the
* wakeup handler expects the vCPU to be on the blocked_vcpu_list that
* matches PI.NDST. Otherwise, a vcpu may not be able to be woken up
* correctly.
*/
if (pi_desc->nv == POSTED_INTR_WAKEUP_VECTOR || vcpu->cpu == cpu) {
pi_clear_sn(pi_desc);
goto after_clear_sn;
}
/* The full case. */
do {
old.control = new.control = pi_desc->control;
@ -1283,6 +1295,8 @@ static void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)
} while (cmpxchg64(&pi_desc->control, old.control,
new.control) != old.control);
after_clear_sn:
/*
* Clear SN before reading the bitmap. The VT-d firmware
* writes the bitmap and reads SN atomically (5.2.3 in the

6
arch/x86/kvm/vmx/vmx.h
View File

@ -373,6 +373,12 @@ static inline void pi_clear_on(struct pi_desc *pi_desc)
(unsigned long *)&pi_desc->control);
}
static inline void pi_clear_sn(struct pi_desc *pi_desc)
{
clear_bit(POSTED_INTR_SN,
(unsigned long *)&pi_desc->control);
}
static inline int pi_test_on(struct pi_desc *pi_desc)
{
return test_bit(POSTED_INTR_ON,