linux-kernel - Re: [PATCH] KVM: X86: Make fpu allocation a common function

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Message-ID: <20191014183723.GE22962@linux.intel.com>
Date:   Mon, 14 Oct 2019 11:37:23 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Xiaoyao Li <xiaoyao.li@...el.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH] KVM: X86: Make fpu allocation a common function

On Mon, Oct 14, 2019 at 06:58:49PM +0200, Vitaly Kuznetsov wrote:
> Xiaoyao Li <xiaoyao.li@...el.com> writes:
> 
> > They are duplicated codes to create vcpu.arch.{user,guest}_fpu in VMX
> > and SVM. Make them common functions.
> >
> > No functional change intended.
> 
> Would it rather make sense to move this code to
> kvm_arch_vcpu_create()/kvm_arch_vcpu_destroy() instead?

Does it make sense?  Yes.  Would it actually work?  No.  Well, not without
other shenanigans.

FPU allocation can't be placed after the call to .create_vcpu() becuase
it's consumed in kvm_arch_vcpu_init().   FPU allocation can't come before
.create_vcpu() because the vCPU struct itself hasn't been allocated.  The
latter could be solved by passed the FPU pointer into .create_vcpu(), but
that's a bit ugly and is not a precedent we want to set.

At a glance, FPU allocation can be moved to kvm_arch_vcpu_init(), maybe
right before the call to fx_init().