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SubjectRe: [PATCH] kvm: add proper frame pointer logic for vmx
On Tue, Jan 15, 2019 at 09:48:45AM -0800, Sean Christopherson wrote:
> On Tue, Jan 15, 2019 at 11:43:20AM -0500, Qian Cai wrote:
> >
> >
> > On 1/15/19 2:13 AM, Paolo Bonzini wrote:
> > > Hmm, maybe like this:
> > >
> > > diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S
> > > index bcef2c7e9bc4..33122fa9d4bd 100644
> > > --- a/arch/x86/kvm/vmx/vmenter.S
> > > +++ b/arch/x86/kvm/vmx/vmenter.S
> > > @@ -26,19 +26,17 @@ ENTRY(vmx_vmenter)
> > > ret
> > >
> > > 2: vmlaunch
> > > +3:
> > > ret
> > >
> > > -3: cmpb $0, kvm_rebooting
> > > - jne 4f
> > > - call kvm_spurious_fault
> > > -4: ret
> > > -
> > > .pushsection .fixup, "ax"
> > > -5: jmp 3b
> > > +4: cmpb $0, kvm_rebooting
> > > + jne 3b
> > > + jmp kvm_spurious_fault
> > > .popsection
> > >
> > > - _ASM_EXTABLE(1b, 5b)
> > > - _ASM_EXTABLE(2b, 5b)
> > > + _ASM_EXTABLE(1b, 4b)
> > > + _ASM_EXTABLE(2b, 4b)
> > >
> > > ENDPROC(vmx_vmenter)
> >
> > No, that will not work. The problem is in vmx.o where I just sent another patch
> > for it.
> >
> > I can see there are five options to solve it.
> >
> > 1) always inline vmx_vcpu_run()
> > 2) always noinline vmx_vcpu_run()
> > 3) add -fdiable-ipa-fnsplit option to Makefile for vmx.o
> > 4) let STACK_FRAME_NON_STANDARD support part.* syntax.
>
> What is ".part." and where does it come from? Searching for information
> is futile, the term is too generic.

And never mind, my eyes glazed over -fdiable-ipa-fnsplit.

> > 5) trim-down vmx_vcpu_run() even more to not causing splitting by GCC.
> >
> > Option 1) and 2) seems give away the decision for user with
> > CONFIG_CC_OPTIMIZE_FOR_(PERFORMANCE/SIZE).
> >
> > Option 3) prevents other functions there for splitting for optimization.
> >
> > Option 4) and 5) seems tricky to implement.
> >
> > I am not more leaning to 3) as only other fuction will miss splitting is
> > vmx_segment_access_rights().

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