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