On Fri, 2021-10-08 at 19:12 -0700, Sean Christopherson wrote:
> Move the WARN sanity checks out of the PI descriptor update loop so as
> not to spam the kernel log if the condition is violated and the update
> takes multiple attempts due to another writer. This also eliminates a
> few extra uops from the retry path.
>
> Technically not checking every attempt could mean KVM will now fail to
> WARN in a scenario that would have failed before, but any such failure
> would be inherently racy as some other agent (CPU or device) would have
> to concurrent modify the PI descriptor.
>
> Signed-off-by: Sean Christopherson <[email protected]>
> ---
> arch/x86/kvm/vmx/posted_intr.c | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/posted_intr.c b/arch/x86/kvm/vmx/posted_intr.c
> index 351666c41bbc..67cbe6ab8f66 100644
> --- a/arch/x86/kvm/vmx/posted_intr.c
> +++ b/arch/x86/kvm/vmx/posted_intr.c
> @@ -100,10 +100,11 @@ static void __pi_post_block(struct kvm_vcpu *vcpu)
> struct pi_desc old, new;
> unsigned int dest;
>
> + WARN(pi_desc->nv != POSTED_INTR_WAKEUP_VECTOR,
> + "Wakeup handler not enabled while the vCPU was blocking");
> +
> do {
> old.control = new.control = pi_desc->control;
> - WARN(old.nv != POSTED_INTR_WAKEUP_VECTOR,
> - "Wakeup handler not enabled while the VCPU is blocked\n");
>
> dest = cpu_physical_id(vcpu->cpu);
>
> @@ -161,13 +162,12 @@ int pi_pre_block(struct kvm_vcpu *vcpu)
> spin_unlock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu));
> }
>
> + WARN(pi_desc->sn == 1,
> + "Posted Interrupt Suppress Notification set before blocking");
> +
> do {
> old.control = new.control = pi_desc->control;
>
> - WARN((pi_desc->sn == 1),
> - "Warning: SN field of posted-interrupts "
> - "is set before blocking\n");
> -
> /*
> * Since vCPU can be preempted during this process,
> * vcpu->cpu could be different with pre_pcpu, we
Don't know for sure if this is desired. I'll would just use WARN_ON_ONCE instead
if the warning spams the log.
If there is a race I would rather want to catch it even if rare.
Best regards,
Maxim Levitsky
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