+cc Josh, for real this time. On Tue, Jan 15, 2019 at 11:06:17AM -0800, Sean Christopherson wrote: > +cc Josh > > Josh, > > The issue we're encountering is that vmx_vcpu_run() is marked with > STACK_FRAME_NON_STANDARD because %rbp is saved/modified/restored when > transitioning to/from the guest. But vmx_vcpu_run() also happens to > be a giant blob of code that gcc will sometime split into separate > .part.* functions, which means that objtool's symbol lookup to whitelist > the function doesn't work. > > 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. > > 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(). > > Option 4) is the most correct, but "tricky" is an understatement. Unless > Josh is willing to pick up the task it'll likely have to wait. > > There's actually a few more options: > > 6) Replace "pop %rbp" in the vmx_vmenter() asm blob with an open-coded > equivalent, e.g. "mov [%rsp], %rbp; add $8, %rsp". This runs an end- > around on objtool since objtool explicitly keys off "pop %rbp" and NOT > "mov ..., %rbp" (which is probably an objtool checking flaw?"). > > 7) Move the vmx_vmenter() asm blob and a few other lines of code into a > separate helper, e.g. __vmx_vcpu_run(), and mark that as having a > non-standard stack frame. > > Option 6) is an ugly (but amusing) hack. > > Arguably we should do option 7) regardless of whether or not objtool gets > updated to support fnsplit behavior, as it it allows objtool to do proper > stack checking on the bulk of vmx_vcpu_run(). And it's a pretty trivial > change. > > I'll send a patch for option 7), which in theory should fix the warning > for all .configs.
