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

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Date:   Fri, 24 Jul 2020 02:46:26 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
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

Sean,

Sean Christopherson <sean.j.christopherson@...el.com> writes:
> On Thu, Jul 23, 2020 at 12:00:09AM +0200, Thomas Gleixner wrote:
>> +		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.

The reason is probably lazyness. The original approach was to have this
as close as possible to user entry/exit but with the recent changes
vs. instrumentation and RCU this is not longer the case.

I really want to keep the notion of transitioning in the function name,
so xfer_to_guest_mode_handle_work() makes a lot of sense.

I'll change that before merging the lot into the tip tree if your
Reviewed-by still stands with that change made w/o reposting.

Thanks,

        tglx