linux-kernel - Re: [PATCH] KVM: x86: User mutex guards to eliminate __kvm_x86_vendor

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Date:   Mon, 30 Oct 2023 16:07:18 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Nikolay Borisov <nik.borisov@...e.com>
Cc:     pbonzini@...hat.com, x86@...nel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: User mutex guards to eliminate __kvm_x86_vendor_init()

On Mon, Oct 30, 2023, Nikolay Borisov wrote:
> Current separation between (__){0,1}kvm_x86_vendor_init() is superfluos as

superfluous

But this intro is actively misleading.  The double-underscore variant most definitely
isn't superfluous, e.g. it eliminates the need for gotos reduces the probability
of incorrect error codes, bugs in the error handling, etc.  It _becomes_ superflous
after switching to guard(mutex).

IMO, this is one of the instances where the "problem, then solution" appoach is
counter-productive.  If there are no objections, I'll massage the change log to
the below when applying (for 6.8, in a few weeks).

  Use the recently introduced guard(mutex) infrastructure acquire and
  automatically release vendor_module_lock when the guard goes out of scope.
  Drop the inner __kvm_x86_vendor_init(), its sole purpose was to simplify
  releasing vendor_module_lock in error paths.

  No functional change intended.

> the the underscore version doesn't have any other callers.
> 
> Instead, use the newly added cleanup infrastructure to ensure that
> kvm_x86_vendor_init() holds the vendor_module_lock throughout its
> exectuion and that in case of error in the middle it's released. No
> functional changes.