linux-kernel - RE: [RFC PATCH v1] KVM: x86: Introduce macros to simplify KVM_X86

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Message-ID: <DS0PR11MB63739BE4347EC6369ED22EBADC0E2@DS0PR11MB6373.namprd11.prod.outlook.com>
Date: Thu, 18 Apr 2024 03:57:52 +0000
From: "Wang, Wei W" <wei.w.wang@...el.com>
To: Sean Christopherson <seanjc@...gle.com>
CC: "pbonzini@...hat.com" <pbonzini@...hat.com>, "kvm@...r.kernel.org"
	<kvm@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [RFC PATCH v1] KVM: x86: Introduce macros to simplify KVM_X86_OPS
 static calls

On Thursday, April 18, 2024 12:27 AM, Sean Christopherson wrote:
> On Wed, Apr 17, 2024, Wei Wang wrote:
> > Introduces two new macros, KVM_X86_SC() and KVM_X86_SCC(), to
> > streamline the usage of KVM_X86_OPS static calls. The current
> > implementation of these calls is verbose and can lead to alignment
> > challenges due to the two pairs of parentheses. This makes the code
> > susceptible to exceeding the "80 columns per single line of code"
> > limit as defined in the coding-style document. The two macros are
> > added to improve code readability and maintainability, while adhering to
> the coding style guidelines.
> 
> Heh, I've considered something similar on multiple occasionsi.  Not because
> the verbosity bothers me, but because I often search for exact "word" matches
> when looking for function usage and the kvm_x86_ prefix trips me up.

Yeah, that's another compelling reason for the improvement.

> IIRC, static_call_cond() is essentially dead code, i.e. it's the exact same as
> static_call().  I believe there's details buried in a proposed series to remove
> it[*].  And to not lead things astray, I verified that invoking a NULL kvm_x86_op
> with static_call() does no harm (well, doesn't explode at least).
> 
> So if we add wrapper macros, I would be in favor in removing all
> static_call_cond() as a prep patch so that we can have a single macro.

Sounds good. Maybe KVM_X86_OP_OPTIONAL could now also be removed? 


> kvm_ops_update() already WARNs if a mandatory hook isn't defined, so doing
> more checks at runtime wouldn't provide any value.

> 
> As for the name, what about KVM_X86_CALL() instead of KVM_X86_SC()?  Two
> extra characters, but should make it much more obvious what's going on for
> readers that aren't familiar with the infrastructure.

I thought the macro definition is quite intuitive and those encountering it for the
first time could get familiar with it easily from the definition.
Similarly, KVM_X86_CALL() is fine to me, despite the fact that it doesn't explicitly
denote "static" calls.

> 
> And I bet we can get away with KVM_PMU_CALL() for the PMU hooks.

Yes, this can be covered as well.