linux-kernel - Re: [PATCH] KVM: VMX: check match table

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Date:   Tue, 26 Sep 2017 10:12:19 -0700
From:   Josh Triplett <josh@...htriplett.org>
To:     Nick Desaulniers <nick.desaulniers@...il.com>
Cc:     kay@...y.org, avi@...hat.com, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] KVM: VMX: check match table

On Mon, Sep 25, 2017 at 09:25:38PM -0700, Nick Desaulniers wrote:
> Fixes the warning:
> arch/x86/kvm/vmx.c:64:32: warning: variable 'vmx_cpu_id' is not needed
> and will not be emitted [-Wunneeded-internal-declaration]``
> 
> Other callers of MODULE_DEVICE_TABLE() seem to check their second
> argument during driver init with the x86_match_cpu() function, if their
> first argument to MODULE_DEVICE_TABLE() is x86cpu.  The documentation
> for x86_match_cpu() seems to agree.
> 
> Suggested-by: Josh Triplett <josh@...htriplett.org>
> Signed-off-by: Nick Desaulniers <nick.desaulniers@...il.com>

Comments below.

> ---
>  arch/x86/kernel/cpu/match.c | 2 +-
>  arch/x86/kvm/vmx.c          | 7 ++++++-
>  2 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/match.c b/arch/x86/kernel/cpu/match.c
> index e42117d5f4d7..fb1aeafa5cc7 100644
> --- a/arch/x86/kernel/cpu/match.c
> +++ b/arch/x86/kernel/cpu/match.c
> @@ -5,7 +5,7 @@
>  #include <linux/slab.h>
>  
>  /**
> - * x86_match_cpu - match current CPU again an array of x86_cpu_ids
> + * x86_match_cpu - match current CPU against an array of x86_cpu_ids

This is a good fix as well, but it shouldn't be in the same commit.

>   * @match: Pointer to array of x86_cpu_ids. Last entry terminated with
>   *         {}.
>   *
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 6970249c09fc..e1a00b130935 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -12074,7 +12074,12 @@ static struct kvm_x86_ops vmx_x86_ops __ro_after_init = {
>  
>  static int __init vmx_init(void)
>  {
> -	int r = kvm_init(&vmx_x86_ops, sizeof(struct vcpu_vmx),
> +	int r;
> +
> +	if (!x86_match_cpu(vmx_cpu_id))
> +		return -ENODEV;

Does this make any other checks redundant and removable?

> +
> +	r = kvm_init(&vmx_x86_ops, sizeof(struct vcpu_vmx),
>                       __alignof__(struct vcpu_vmx), THIS_MODULE);
>  	if (r)
>  		return r;
> -- 
> 2.11.0
>