linux-kernel - Re: [patch V5 15/15] x86/kvm: Use generic xfer to guest work function

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Message-ID: <20200724001736.GK21891@linux.intel.com>
Date:   Thu, 23 Jul 2020 17:17:36 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        linux-arch@...r.kernel.org, Will Deacon <will@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Mark Rutland <mark.rutland@....com>,
        Kees Cook <keescook@...omium.org>,
        Keno Fischer <keno@...iacomputing.com>,
        Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        Gabriel Krisman Bertazi <krisman@...labora.com>
Subject: Re: [patch V5 15/15] x86/kvm: Use generic xfer to guest work function

On Thu, Jul 23, 2020 at 12:00:09AM +0200, Thomas Gleixner wrote:
> From: Thomas Gleixner <tglx@...utronix.de>
> 
> Use the generic infrastructure to check for and handle pending work before
> transitioning into guest mode.
> 
> This now handles TIF_NOTIFY_RESUME as well which was ignored so
> far. Handling it is important as this covers task work and task work will
> be used to offload the heavy lifting of POSIX CPU timers to thread context.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
> V5: Rename exit -> xfer
> ---

One nit/question below (though it's really about patch 5).

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

> @@ -8676,15 +8677,11 @@ static int vcpu_run(struct kvm_vcpu *vcp
>  			break;
>  		}
>  
> -		if (signal_pending(current)) {
> -			r = -EINTR;
> -			vcpu->run->exit_reason = KVM_EXIT_INTR;
> -			++vcpu->stat.signal_exits;
> -			break;
> -		}
> -		if (need_resched()) {
> +		if (xfer_to_guest_mode_work_pending()) {
>  			srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
> -			cond_resched();
> +			r = xfer_to_guest_mode(vcpu);

Any reason not to call this xfer_to_guest_mode_work()?  Or handle_work(),
do_work(), etc...  Without the "work" part, it looks like a function that
should be invoked unconditionally.  It's obvious that's not the case if
one looks at the implementation, but it's a bit confusing on the KVM side
of things.

> +			if (r)
> +				return r;
>  			vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
>  		}
>  	}
>