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

[Rick Edgecombe]

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.

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;
-	}
-
 	/* 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