On Mon, Sep 14, 2020 at 9:56 PM Sean Christopherson
<sean.j.christopherson@xxxxxxxxx> 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
_ASM_SP instead of %rsp to avoid assembly failure for 32bit targets.
> +
> +#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
> +SYM_FUNC_END(vmx_do_interrupt_nmi_irqoff)
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 46ba2e03a892..391f079d9136 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6409,6 +6409,8 @@ static void vmx_apicv_post_state_restore(struct kvm_vcpu *vcpu)
> memset(vmx->pi_desc.pir, 0, sizeof(vmx->pi_desc.pir));
> }
>
> +void vmx_do_interrupt_nmi_irqoff(unsigned long entry);
> +
> static void handle_exception_nmi_irqoff(struct vcpu_vmx *vmx)
> {
> u32 intr_info = vmx_get_intr_info(&vmx->vcpu);
> @@ -6430,10 +6432,6 @@ static void handle_exception_nmi_irqoff(struct vcpu_vmx *vmx)
> static void handle_external_interrupt_irqoff(struct kvm_vcpu *vcpu)
> {
> unsigned int vector;
> - unsigned long entry;
> -#ifdef CONFIG_X86_64
> - unsigned long tmp;
> -#endif
> gate_desc *desc;
> u32 intr_info = vmx_get_intr_info(vcpu);
>
> @@ -6443,36 +6441,11 @@ static void handle_external_interrupt_irqoff(struct kvm_vcpu *vcpu)
>
> vector = intr_info & INTR_INFO_VECTOR_MASK;
> desc = (gate_desc *)host_idt_base + vector;
> - entry = gate_offset(desc);
I'd leave the above line...
>
> kvm_before_interrupt(vcpu);
> -
> - asm volatile(
> -#ifdef CONFIG_X86_64
> - "mov %%rsp, %[sp]\n\t"
> - "and $-16, %%rsp\n\t"
> - "push %[ss]\n\t"
> - "push %[sp]\n\t"
> -#endif
> - "pushf\n\t"
> - "push %[cs]\n\t"
> - CALL_NOSPEC
> - :
> -#ifdef CONFIG_X86_64
> - [sp]"=&r"(tmp),
> -#endif
> - ASM_CALL_CONSTRAINT
> - :
> - [thunk_target]"r"(entry),
> -#ifdef CONFIG_X86_64
> - [ss]"i"(__KERNEL_DS),
> -#endif
> - [cs]"i"(__KERNEL_CS)
> - );
> -
> + vmx_do_interrupt_nmi_irqoff(gate_offset(desc));
... to make the above line read as:
vmx_do_interrupt_nmi_irqoff(entry);
This way, it looks more descriptive to me.
Uros.
> kvm_after_interrupt(vcpu);
> }
> -STACK_FRAME_NON_STANDARD(handle_external_interrupt_irqoff);
>
> static void vmx_handle_exit_irqoff(struct kvm_vcpu *vcpu)
> {
> --
> 2.28.0
>
