On Mon, Sep 14, 2020 at 11:07 PM Sean Christopherson <sean.j.christopherson@xxxxxxxxx> wrote: > > On Mon, Sep 14, 2020 at 03:40:24PM -0500, Josh Poimboeuf wrote: > > 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? > > Ah, yeah, that's lacking info. > > 16-byte aligned to correctly mimic CPU behavior when vectoring an IRQ/NMI. > When not changing stack, the CPU aligns RSP before pushing the frame. > > The above shenanigans work because the x86-64 ABI also requires RSP to be > 16-byte aligned prior to CALL. RSP is thus 8-byte aligned due to CALL > pushing the return IP, and so creating the stack frame by pushing RBP makes > it 16-byte aliagned again. IIRC, the kernel violates x86_64 ABI and aligns RSP to 8 bytes prior to CALL. Please note -mpreferred-stack-boundary=3 in the compile flags. Uros.
