Messages in this thread | | | Date | Mon, 15 Jul 2019 07:37:04 -0500 | From | Josh Poimboeuf <> | Subject | Re: [PATCH 03/22] x86/kvm: Fix frame pointer usage in vmx_vmenter() |
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On Mon, Jul 15, 2019 at 11:04:03AM +0200, Paolo Bonzini wrote: > 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@redhat.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
Ah, that is surprising :-)
And then there's this, which overwrites the frame pointer anyway:
mov VCPU_RBP(%_ASM_AX), %_ASM_BP
Would it make sense to remove the call to vmx_vmenter() altogether, and just either embed it in __vmx_vcpu_run(), or jmp back and forth to it from __vmx_vcpu_run()?
Then you could get rid of the RSP adjustment hack, and the vmx_update_host_rsp() function altogether.
> Is this important since kvm_spurious_fault is just BUG()?
It's probably only important if you care about the stack trace for the BUG() case. But BP is clobbered anyway so I guess it doesn't matter.
> 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.
That would be one way to make objtool happy.
-- Josh
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