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Subject[PATCH v2 1/2] KVM: VMX: Move IRQ invocation to assembly subroutine
Date
Move the asm blob that invokes the appropriate IRQ handler after VM-Exit
into a proper subroutine. Unconditionally create a stack frame in the
subroutine so that, as objtool sees things, the function has standard
stack behavior. The dynamic stack adjustment makes using unwind hints
problematic.

Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/kvm/vmx/vmenter.S | 34 ++++++++++++++++++++++++++++++++++
arch/x86/kvm/vmx/vmx.c | 33 +++------------------------------
2 files changed, 37 insertions(+), 30 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S
index 799db084a336..90ad7a6246e3 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 +295,36 @@ 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, getting the correct RSP on the
+ * stack (for x86-64) would take two instructions anyways, and RBP can
+ * be used to restore RSP to make objtool happy (see below).
+ */
+ push %_ASM_BP
+ mov %_ASM_SP, %_ASM_BP
+
+#ifdef CONFIG_X86_64
+ /*
+ * Align RSP to a 16-byte boundary (to emulate CPU behavior) before
+ * creating the synthetic interrupt stack frame for the IRQ/NMI.
+ */
+ and $-16, %rsp
+ push $__KERNEL_DS
+ push %rbp
+#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 callee will IRET and,
+ * without the explicit restore, thinks the stack is getting walloped.
+ * Using an unwind hint is problematic due to x86-64's dynamic alignment.
+ */
+ mov %_ASM_BP, %_ASM_SP
+ 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);

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));
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
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