linux-kernel - Re: [PATCH 1/2] KVM: VMX: Move IRQ invocation to assembly subroutine

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Date:   Mon, 14 Sep 2020 14:08:08 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Uros Bizjak <ubizjak@...il.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 1/2] KVM: VMX: Move IRQ invocation to assembly subroutine

On Mon, Sep 14, 2020 at 10:37:25PM +0200, Uros Bizjak wrote:
> On Mon, Sep 14, 2020 at 9:56 PM Sean Christopherson
> <sean.j.christopherson@...el.com> wrote:
> >
> > Move the asm blob that invokes the appropriate IRQ handler after VM-Exit
> > into a proper subroutine.  Slightly rework the blob so that it plays
> > nice with objtool without any additional hints (existing hints aren't
> > able to handle returning with a seemingly modified stack size).
> >
> > Suggested-by: Josh Poimboeuf <jpoimboe@...hat.com>
> > Cc: Uros Bizjak <ubizjak@...il.com>
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> > ---
> >  arch/x86/kvm/vmx/vmenter.S | 28 ++++++++++++++++++++++++++++
> >  arch/x86/kvm/vmx/vmx.c     | 33 +++------------------------------
> >  2 files changed, 31 insertions(+), 30 deletions(-)
> >
> > diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S
> > index 799db084a336..baec1e0fefc5 100644
> > --- a/arch/x86/kvm/vmx/vmenter.S
> > +++ b/arch/x86/kvm/vmx/vmenter.S
> > @@ -4,6 +4,7 @@
> >  #include <asm/bitsperlong.h>
> >  #include <asm/kvm_vcpu_regs.h>
> >  #include <asm/nospec-branch.h>
> > +#include <asm/segment.h>
> >
> >  #define WORD_SIZE (BITS_PER_LONG / 8)
> >
> > @@ -294,3 +295,30 @@ SYM_FUNC_START(vmread_error_trampoline)
> >
> >         ret
> >  SYM_FUNC_END(vmread_error_trampoline)
> > +
> > +SYM_FUNC_START(vmx_do_interrupt_nmi_irqoff)
> > +       /*
> > +        * Unconditionally create a stack frame.  RSP needs to be aligned for
> > +        * x86-64, getting the correct RSP on the stack (for x86-64) would take
> > +        * two instructions anyways, and it helps make objtool happy (see below).
> > +        */
> > +       push %_ASM_BP
> > +       mov %rsp, %_ASM_BP
> 
> _ASM_SP instead of %rsp to avoid assembly failure for 32bit targets.

*sigh*  Thanks!  I'll build i386 this time...