linux-kernel - Re: [PATCH 03/22] x86/kvm: Fix frame pointer usage in vmx

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Message-ID: <0b37031b-1043-8274-a086-2b5d0b02b5ef@redhat.com>
Date:   Mon, 15 Jul 2019 11:04:03 +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 03/22] x86/kvm: Fix frame pointer usage in vmx_vmenter()

On 15/07/19 02:36, Josh Poimboeuf wrote:
> With CONFIG_FRAME_POINTER, vmx_vmenter() needs to do frame pointer setup
> before calling kvm_spurious_fault().
> 
> Fixes the following warning:
> 
>   arch/x86/kvm/vmx/vmenter.o: warning: objtool: vmx_vmenter()+0x14: call without frame pointer save/setup
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>

This is not enough, because the RSP value must match what is computed at
this place:

        /* Adjust RSP to account for the CALL to vmx_vmenter(). */
        lea -WORD_SIZE(%_ASM_SP), %_ASM_ARG2
        call vmx_update_host_rsp

Is this important since kvm_spurious_fault is just BUG()?  There is no
macro currently to support CONFIG_DEBUG_BUGVERBOSE in assembly code, but
it's also fine if you just change the call to ud2.

Paolo