Re: [PATCH 4/4] KVM: x86: Disable the TDX module during kexec and kdump

[Chao Gao]

A few nits below:

The scope "KVM: x86" is wrong as this doesn't touch any KVM code.

On Fri, Mar 06, 2026 at 05:03:58PM -0800, Rick Edgecombe wrote:
>From: Vishal Verma <vishal.l.verma@xxxxxxxxx>
>
>Use the TDH.SYS.DISABLE SEAMCALL, which disables the TDX module,
>reclaims all memory resources assigned to TDX, and clears any
>partial-write induced poison, to allow kexec and kdump on platforms with
>the partial write errata.
>
>On TDX-capable platforms with the partial write erratum, kexec has been
>disabled because the new kernel could hit a machine check reading a
>previously poisoned memory location.
>
>Later TDX modules support TDH.SYS.DISABLE, which disables the module and
>reclaims all TDX memory resources, allowing the new kernel to re-initialize
>TDX from scratch. This operation also clears the old memory, cleaning up
>any poison.
>
>Add tdx_sys_disable() to tdx_shutdown(), which is called in the
>syscore_shutdown path for kexec. This is done just before tdx_shutdown()
>disables VMX on all CPUs.
>
>For kdump, call tdx_sys_disable() in the crash path before
>x86_virt_emergency_disable_virtualization_cpu() does VMXOFF.
>
>Since this clears any poison on TDX-managed memory, the
>X86_BUG_TDX_PW_MCE check in machine_kexec() that blocked kexec on
>partial write errata platforms can be removed.

Use imperative mood here: "Since ..., remove the X86_BUG_TDX_PW_MCE check..."

>
>Signed-off-by: Vishal Verma <vishal.l.verma@xxxxxxxxx>
>Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
>---
> arch/x86/kernel/crash.c            |  2 ++
> arch/x86/kernel/machine_kexec_64.c | 16 ----------------
> arch/x86/virt/vmx/tdx/tdx.c        |  1 +
> 3 files changed, 3 insertions(+), 16 deletions(-)
>
>diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
>index cd796818d94d..623d4474631a 100644
>--- a/arch/x86/kernel/crash.c
>+++ b/arch/x86/kernel/crash.c
>@@ -38,6 +38,7 @@
> #include <linux/kdebug.h>
> #include <asm/cpu.h>
> #include <asm/reboot.h>
>+#include <asm/tdx.h>
> #include <asm/intel_pt.h>
> #include <asm/crash.h>
> #include <asm/cmdline.h>
>@@ -112,6 +113,7 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
> 
> 	crash_smp_send_stop();
> 
>+	tdx_sys_disable();
> 	x86_virt_emergency_disable_virtualization_cpu();
> 
> 	/*
>diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
>index 0590d399d4f1..c3f4a389992d 100644
>--- a/arch/x86/kernel/machine_kexec_64.c
>+++ b/arch/x86/kernel/machine_kexec_64.c
>@@ -347,22 +347,6 @@ int machine_kexec_prepare(struct kimage *image)
> 	unsigned long reloc_end = (unsigned long)__relocate_kernel_end;
> 	int result;
> 
>-	/*
>-	 * Some early TDX-capable platforms have an erratum.  A kernel
>-	 * partial write (a write transaction of less than cacheline
>-	 * lands at memory controller) to TDX private memory poisons that
>-	 * memory, and a subsequent read triggers a machine check.
>-	 *
>-	 * On those platforms the old kernel must reset TDX private
>-	 * memory before jumping to the new kernel otherwise the new
>-	 * kernel may see unexpected machine check.  For simplicity
>-	 * just fail kexec/kdump on those platforms.
>-	 */
>-	if (boot_cpu_has_bug(X86_BUG_TDX_PW_MCE)) {
>-		pr_info_once("Not allowed on platform with tdx_pw_mce bug\n");
>-		return -EOPNOTSUPP;
>-	}

With this series, we need to update the "Kexec" section in tdx.rst.

>-
> 	/* Setup the identity mapped 64bit page table */
> 	result = init_pgtable(image, __pa(control_page));
> 	if (result)
>diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
>index 68bd2618dde4..b388fbce5d76 100644
>--- a/arch/x86/virt/vmx/tdx/tdx.c
>+++ b/arch/x86/virt/vmx/tdx/tdx.c
>@@ -252,6 +252,7 @@ static void tdx_shutdown_cpu(void *ign)
> 
> static void tdx_shutdown(void *ign)
> {
>+	tdx_sys_disable();
> 	on_each_cpu(tdx_shutdown_cpu, NULL, 1);
> }
> 
>-- 
>2.53.0
>