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SubjectRe: [PATCH] kvm: add proper frame pointer logic for vmx
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.

> 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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