linux-kernel - Re: [PATCH v2 03/22] x86/kvm: Replace vmx_vmenter()'s call to kvm_spurious

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Date:   Thu, 18 Jul 2019 10:17:46 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Arnd Bergmann <arnd@...db.de>, Jann Horn <jannh@...gle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH v2 03/22] x86/kvm: Replace vmx_vmenter()'s call to
 kvm_spurious_fault() with UD2

On 18/07/19 03:36, Josh Poimboeuf wrote:
> Objtool reports the following:
> 
>   arch/x86/kvm/vmx/vmenter.o: warning: objtool: vmx_vmenter()+0x14: call without frame pointer save/setup
> 
> But frame pointers are necessarily broken anyway, because
> __vmx_vcpu_run() clobbers RBP with the guest's value before calling
> vmx_vmenter().  So calling without a frame pointer doesn't make things
> any worse.
> 
> Make objtool happy by changing the call to a UD2.
> 
> Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
> v2: ud2 instead of kvm_spurious_fault() [Paolo]
> 
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> ---
>  arch/x86/kvm/vmx/vmenter.S | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S
> index d4cb1945b2e3..4010d519eb8c 100644
> --- a/arch/x86/kvm/vmx/vmenter.S
> +++ b/arch/x86/kvm/vmx/vmenter.S
> @@ -54,9 +54,9 @@ ENTRY(vmx_vmenter)
>  	ret
>  
>  3:	cmpb $0, kvm_rebooting
> -	jne 4f
> -	call kvm_spurious_fault
> -4:	ret
> +	je 4f
> +	ret
> +4:	ud2
>  
>  	.pushsection .fixup, "ax"
>  5:	jmp 3b
> 

Acked-by: Paolo Bonzini <pbonzini@...hat.com>