Re: [PATCH v4 1/6] KVM: x86: Introduce KVM_REQ_RING_SOFT_FULL

[Marc Zyngier <maz@kernel.org>]

On Mon, 26 Sep 2022 20:54:34 -0400,
Gavin Shan <gshan@redhat.com> wrote:
> 
> This adds KVM_REQ_RING_SOFT_FULL, which is raised when the dirty
> ring of the specific VCPU becomes softly full in kvm_dirty_ring_push().
> The VCPU is enforced to exit when the request is raised and its
> dirty ring is softly full on its entrance.
> 
> The event is checked and handled in the newly introduced helper
> kvm_dirty_ring_check_request(). With this, kvm_dirty_ring_soft_full()
> becomes a private function.
> 
> Suggested-by: Marc Zyngier <maz@kernel.org>
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> ---
>  arch/x86/kvm/x86.c             | 15 ++++++---------
>  include/linux/kvm_dirty_ring.h | 13 +++++++------
>  include/linux/kvm_host.h       |  1 +
>  virt/kvm/dirty_ring.c          | 19 ++++++++++++++++++-
>  4 files changed, 32 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index b0c47b41c264..0dd0d32073e7 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10260,16 +10260,13 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  
>  	bool req_immediate_exit = false;
>  
> -	/* Forbid vmenter if vcpu dirty ring is soft-full */
> -	if (unlikely(vcpu->kvm->dirty_ring_size &&
> -		     kvm_dirty_ring_soft_full(&vcpu->dirty_ring))) {
> -		vcpu->run->exit_reason = KVM_EXIT_DIRTY_RING_FULL;
> -		trace_kvm_dirty_ring_exit(vcpu);
> -		r = 0;
> -		goto out;
> -	}
> -
>  	if (kvm_request_pending(vcpu)) {
> +		/* Forbid vmenter if vcpu dirty ring is soft-full */
> +		if (kvm_dirty_ring_check_request(vcpu)) {
> +			r = 0;
> +			goto out;
> +		}
> +
>  		if (kvm_check_request(KVM_REQ_VM_DEAD, vcpu)) {
>  			r = -EIO;
>  			goto out;
> diff --git a/include/linux/kvm_dirty_ring.h b/include/linux/kvm_dirty_ring.h
> index 906f899813dc..b188bfcf3a09 100644
> --- a/include/linux/kvm_dirty_ring.h
> +++ b/include/linux/kvm_dirty_ring.h
> @@ -54,6 +54,11 @@ static inline void kvm_dirty_ring_push(struct kvm_dirty_ring *ring,
>  {
>  }
>  
> +static inline bool kvm_dirty_ring_check_request(struct kvm_vcpu *vcpu)
> +{
> +	return false;
> +}
> +

nit: I don't think this is needed at all. The dirty ring feature is
not user-selectable, and this is always called from arch code that is
fully aware of that option.

This can be fixed when applying the patch though, no need to resend
for this.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.
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