linux-kernel - Re: [PATCH 1/2] KVM: async_pf: Cleanup kvm_setup_async

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Date:   Wed, 10 Jun 2020 11:14:53 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Vivek Goyal <vgoyal@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] KVM: async_pf: Cleanup kvm_setup_async_pf()

On Wed, Jun 10, 2020 at 07:55:31PM +0200, Vitaly Kuznetsov wrote:
> schedule_work() returns 'false' only when the work is already on the queue
> and this can't happen as kvm_setup_async_pf() always allocates a new one.
> Also, to avoid potential race, it makes sense to to schedule_work() at the
> very end after we've added it to the queue.
> 
> While on it, do some minor cleanup. gfn_to_pfn_async() mentioned in a
> comment does not currently exist and, moreover, we can check
> kvm_is_error_hva() at the very beginning, before we try to allocate work so
> 'retry_sync' label can go away completely.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  virt/kvm/async_pf.c | 19 ++++++-------------
>  1 file changed, 6 insertions(+), 13 deletions(-)
> 
> diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
> index f1e07fae84e9..ba080088da76 100644
> --- a/virt/kvm/async_pf.c
> +++ b/virt/kvm/async_pf.c
> @@ -164,7 +164,9 @@ int kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
>  	if (vcpu->async_pf.queued >= ASYNC_PF_PER_VCPU)
>  		return 0;
>  
> -	/* setup delayed work */
> +	/* Arch specific code should not do async PF in this case */
> +	if (unlikely(kvm_is_error_hva(hva)))

This feels like it should be changed to a WARN_ON_ONCE in a follow-up.
With the WARN, the comment could probably be dropped.

I'd also be in favor of changing the return type to a boolean.  I think
you alluded to it earlier, the current semantics are quite confusing as they
invert the normal "return 0 on success".

For this patch:

Reviewed-by: Sean Christopherson <sean.j.christopherson@...el.com>