On Mon, Sep 14, 2020 at 12:56:33PM -0700, Sean Christopherson wrote: > Move the asm blob that invokes the appropriate IRQ handler after VM-Exit > into a proper subroutine. Slightly rework the blob so that it plays > nice with objtool without any additional hints (existing hints aren't > able to handle returning with a seemingly modified stack size). > > Suggested-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> > Cc: Uros Bizjak <ubizjak@xxxxxxxxx> > Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx> > --- > arch/x86/kvm/vmx/vmenter.S | 28 ++++++++++++++++++++++++++++ > arch/x86/kvm/vmx/vmx.c | 33 +++------------------------------ > 2 files changed, 31 insertions(+), 30 deletions(-) > > diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S > index 799db084a336..baec1e0fefc5 100644 > --- a/arch/x86/kvm/vmx/vmenter.S > +++ b/arch/x86/kvm/vmx/vmenter.S > @@ -4,6 +4,7 @@ > #include <asm/bitsperlong.h> > #include <asm/kvm_vcpu_regs.h> > #include <asm/nospec-branch.h> > +#include <asm/segment.h> > > #define WORD_SIZE (BITS_PER_LONG / 8) > > @@ -294,3 +295,30 @@ SYM_FUNC_START(vmread_error_trampoline) > > ret > SYM_FUNC_END(vmread_error_trampoline) > + > +SYM_FUNC_START(vmx_do_interrupt_nmi_irqoff) > + /* > + * Unconditionally create a stack frame. RSP needs to be aligned for > + * x86-64, getting the correct RSP on the stack (for x86-64) would take > + * two instructions anyways, and it helps make objtool happy (see below). > + */ > + push %_ASM_BP > + mov %rsp, %_ASM_BP RSP needs to be aligned to what? How would this align the stack, other than by accident? > + > +#ifdef CONFIG_X86_64 > + push $__KERNEL_DS > + push %_ASM_BP > +#endif > + pushf > + push $__KERNEL_CS > + CALL_NOSPEC _ASM_ARG1 > + > + /* > + * "Restore" RSP from RBP, even though IRET has already unwound RSP to > + * the correct value. objtool doesn't know the target will IRET and so > + * thinks the stack is getting walloped (without the explicit restore). > + */ > + mov %_ASM_BP, %rsp > + pop %_ASM_BP > + ret BTW, there *is* actually an unwind hint for this situation: UNWIND_HINT_RET_OFFSET. So you might be able to do something like the following (depending on what your alignment requirements actually are): SYM_FUNC_START(vmx_do_interrupt_nmi_irqoff) #ifdef CONFIG_X86_64 push $__KERNEL_DS push %_ASM_BP #endif pushf push $__KERNEL_CS CALL_NOSPEC _ASM_ARG1 /* The call popped the pushes */ UNWIND_HINT_RET_OFFSET sp_offset=32 ret SYM_FUNC_END(vmx_do_interrupt_nmi_irqoff) -- Josh
