linux-kernel - [PATCH v2 17/20] KVM: TDX: Add a method to ignore hypercall patching

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Message-ID: <20250227012021.1778144-18-binbin.wu@linux.intel.com>
Date: Thu, 27 Feb 2025 09:20:18 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: pbonzini@...hat.com,
	seanjc@...gle.com,
	kvm@...r.kernel.org
Cc: rick.p.edgecombe@...el.com,
	kai.huang@...el.com,
	adrian.hunter@...el.com,
	reinette.chatre@...el.com,
	xiaoyao.li@...el.com,
	tony.lindgren@...el.com,
	isaku.yamahata@...el.com,
	yan.y.zhao@...el.com,
	chao.gao@...el.com,
	linux-kernel@...r.kernel.org,
	binbin.wu@...ux.intel.com
Subject: [PATCH v2 17/20] KVM: TDX: Add a method to ignore hypercall patching

From: Isaku Yamahata <isaku.yamahata@...el.com>

Because guest TD memory is protected, VMM patching guest binary for
hypercall instruction isn't possible.  Add a method to ignore hypercall
patching.  Note: guest TD kernel needs to be modified to use
TDG.VP.VMCALL for hypercall.

Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
Signed-off-by: Binbin Wu <binbin.wu@...ux.intel.com>
---
TDX "the rest" v2:
- No change.

TDX "the rest" v1:
- Renamed from
  "KVM: TDX: Add a method to ignore for TDX to ignore hypercall patch"
  to "KVM: TDX: Add a method to ignore hypercall patching".
- Dropped KVM_BUG_ON() in vt_patch_hypercall(). (Rick)
- Remove "with a warning" from "Add a method to ignore hypercall
  patching with a warning." in changelog to reflect code change.
---
 arch/x86/kvm/vmx/main.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
index d73ea9ce750d..fa8b5f609666 100644
--- a/arch/x86/kvm/vmx/main.c
+++ b/arch/x86/kvm/vmx/main.c
@@ -673,6 +673,19 @@ static u32 vt_get_interrupt_shadow(struct kvm_vcpu *vcpu)
 	return vmx_get_interrupt_shadow(vcpu);
 }
 
+static void vt_patch_hypercall(struct kvm_vcpu *vcpu,
+				  unsigned char *hypercall)
+{
+	/*
+	 * Because guest memory is protected, guest can't be patched. TD kernel
+	 * is modified to use TDG.VP.VMCALL for hypercall.
+	 */
+	if (is_td_vcpu(vcpu))
+		return;
+
+	vmx_patch_hypercall(vcpu, hypercall);
+}
+
 static void vt_inject_irq(struct kvm_vcpu *vcpu, bool reinjected)
 {
 	if (is_td_vcpu(vcpu))
@@ -952,7 +965,7 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
 	.update_emulated_instruction = vmx_update_emulated_instruction,
 	.set_interrupt_shadow = vt_set_interrupt_shadow,
 	.get_interrupt_shadow = vt_get_interrupt_shadow,
-	.patch_hypercall = vmx_patch_hypercall,
+	.patch_hypercall = vt_patch_hypercall,
 	.inject_irq = vt_inject_irq,
 	.inject_nmi = vt_inject_nmi,
 	.inject_exception = vt_inject_exception,
-- 
2.46.0