linux-kernel - Re: [PATCH 02/22] kvm: mmu: Introduce tdp

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Date:   Sat, 26 Sep 2020 02:54:19 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Ben Gardon <bgardon@...gle.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Cannon Matthews <cannonmatthews@...gle.com>,
        Peter Xu <peterx@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Peter Shier <pshier@...gle.com>,
        Peter Feiner <pfeiner@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Yulei Zhang <yulei.kernel@...il.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>
Subject: Re: [PATCH 02/22] kvm: mmu: Introduce tdp_iter

On 25/09/20 23:22, Ben Gardon wrote:
> +	bool done;
> +
> +	done = try_step_down(iter);
> +	if (done)
> +		return;
> +
> +	done = try_step_side(iter);
> +	while (!done) {
> +		if (!try_step_up(iter)) {
> +			iter->valid = false;
> +			break;
> +		}
> +		done = try_step_side(iter);

Seems easier to read without the "done" boolean:

	if (try_step_down(iter))
		return;

	do {
		/* Maybe try_step_right? :) */
		if (try_step_side(iter))
			return;
	} while (try_step_up(iter));
	iter->valid = false;

Also it may be worth adding an "end_level" argument to the constructor,
and checking against it in try_step_down instead of using PG_LEVEL_4K.
By passing in PG_LEVEL_2M, you can avoid adding
tdp_iter_next_no_step_down in patch 17 and generally simplify the logic
there.

Paolo