linux-kernel - Re: [PATCH] kvm/vmx: Make setup/unsetup under the same conditions

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Message-ID: <Yg/GmgbmLKTRqUbo@google.com>
Date:   Fri, 18 Feb 2022 16:17:30 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Peng Hao <flyingpenghao@...il.com>
Cc:     pbonzini@...hat.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH]  kvm/vmx: Make setup/unsetup under the same conditions

"KVM: VMX" for the scope, or maybe even "KVM: nVMX:" despite this not touching
vmx/nested.c.  Either way (but not "kvm/vmx:").

On Fri, Feb 18, 2022, Peng Hao wrote:
> Make sure nested_vmx_hardware_setup/unsetup are called in pairs under
> the same conditions.

Probably worth adding a sentence to clarify that the existing code isn't buggy
only because free_page() plays nice with getting passed '0' and vmx_bitmap is
initialized to zero.  Something like:

  Make sure nested_vmx_hardware_setup/unsetup() are called in pairs under
  the same conditions.  Calling nested_vmx_hardware_unsetup() when nested
  is false "works" right now because it only calls free_page() on zero-
  initialized pointers, but it's possible that more code will be added to
  nested_vmx_hardware_unsetup() in the future.

Reviewed-by: Sean Christopherson <seanjc@...gle.com>

> 
> Signed-off-by: Peng Hao <flyingpeng@...cent.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 0ffcfe54eea5..5392def71093 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7852,7 +7852,7 @@ static __init int hardware_setup(void)
>  	vmx_set_cpu_caps();
>  
>  	r = alloc_kvm_area();
> -	if (r)
> +	if (r && nested)
>  		nested_vmx_hardware_unsetup();
>  
>  	kvm_set_posted_intr_wakeup_handler(pi_wakeup_handler);
> -- 
> 2.27.0
>