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Peter Anvin" Subject: [PATCH v3 07/26] x86/virt/seamldr: Introduce a wrapper for P-SEAMLDR SEAMCALLs Date: Fri, 23 Jan 2026 06:55:15 -0800 Message-ID: <20260123145645.90444-8-chao.gao@intel.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260123145645.90444-1-chao.gao@intel.com> References: <20260123145645.90444-1-chao.gao@intel.com> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Software needs to talk with P-SEAMLDR via P-SEAMLDR SEAMCALLs. So, add a wrapper for P-SEAMLDR SEAMCALLs. Save and restore the current VMCS using VMPTRST and VMPTRLD instructions to avoid breaking KVM. Doing so is because P-SEAMLDR SEAMCALLs would invalidate the current VMCS as documented in Intel® Trust Domain CPU Architectural Extensions (May 2021 edition) Chapter 2.3 [1]: SEAMRET from the P-SEAMLDR clears the current VMCS structure pointed to by the current-VMCS pointer. A VMM that invokes the P-SEAMLDR using SEAMCALL must reload the current-VMCS, if required, using the VMPTRLD instruction. Disable interrupts to prevent KVM code from interfering with P-SEAMLDR SEAMCALLs. For example, if a vCPU is scheduled before the current VMCS is restored, it may encounter an invalid current VMCS, causing its VMX instruction to fail. Additionally, if KVM sends IPIs to invalidate a current VMCS and the invalidation occurs right after the current VMCS is saved, that VMCS will be reloaded after P-SEAMLDR SEAMCALLs, leading to unexpected behavior. NMIs are not a problem, as the only scenario where instructions relying on the current-VMCS are used is during guest PMI handling in KVM. This occurs immediately after VM exits with IRQ and NMI disabled, ensuring no interference with P-SEAMLDR SEAMCALLs. Signed-off-by: Chao Gao Tested-by: Farrah Chen Link: https://cdrdv2.intel.com/v1/dl/getContent/733582 # [1] --- v2: - don't create a new, inferior framework to save/restore VMCS - use human-friendly language, just "current VMCS" rather than SDM term "current-VMCS pointer" - don't mix guard() with goto --- arch/x86/virt/vmx/tdx/Makefile | 1 + arch/x86/virt/vmx/tdx/seamldr.c | 56 ++++++++++++++++++++++++++++++ drivers/virt/coco/tdx-host/Kconfig | 10 ++++++ 3 files changed, 67 insertions(+) create mode 100644 arch/x86/virt/vmx/tdx/seamldr.c diff --git a/arch/x86/virt/vmx/tdx/Makefile b/arch/x86/virt/vmx/tdx/Makefile index 90da47eb85ee..26aea3531c36 100644 --- a/arch/x86/virt/vmx/tdx/Makefile +++ b/arch/x86/virt/vmx/tdx/Makefile @@ -1,2 +1,3 @@ # SPDX-License-Identifier: GPL-2.0-only obj-y += seamcall.o tdx.o +obj-$(CONFIG_INTEL_TDX_MODULE_UPDATE) += seamldr.o diff --git a/arch/x86/virt/vmx/tdx/seamldr.c b/arch/x86/virt/vmx/tdx/seamldr.c new file mode 100644 index 000000000000..b99d73f7bb08 --- /dev/null +++ b/arch/x86/virt/vmx/tdx/seamldr.c @@ -0,0 +1,56 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright(c) 2025 Intel Corporation. + * + * Intel TDX module runtime update + */ +#define pr_fmt(fmt) "seamldr: " fmt + +#include +#include + +#include "seamcall.h" + +static __maybe_unused int seamldr_call(u64 fn, struct tdx_module_args *args) +{ + unsigned long flags; + u64 vmcs; + int ret; + + if (!is_seamldr_call(fn)) + return -EINVAL; + + /* + * SEAMRET from P-SEAMLDR invalidates the current VMCS. Save/restore + * the VMCS across P-SEAMLDR SEAMCALLs to avoid clobbering KVM state. + * Disable interrupts as KVM is allowed to do VMREAD/VMWRITE in IRQ + * context (but not NMI context). + */ + local_irq_save(flags); + + asm goto("1: vmptrst %0\n\t" + _ASM_EXTABLE(1b, %l[error]) + : "=m" (vmcs) : : "cc" : error); + + ret = seamldr_prerr(fn, args); + + /* + * Restore the current VMCS pointer. VMPTSTR "returns" all ones if the + * current VMCS is invalid. + */ + if (vmcs != -1ULL) { + asm goto("1: vmptrld %0\n\t" + "jna %l[error]\n\t" + _ASM_EXTABLE(1b, %l[error]) + : : "m" (vmcs) : "cc" : error); + } + + local_irq_restore(flags); + return ret; + +error: + local_irq_restore(flags); + + WARN_ONCE(1, "Failed to save/restore the current VMCS"); + return -EIO; +} diff --git a/drivers/virt/coco/tdx-host/Kconfig b/drivers/virt/coco/tdx-host/Kconfig index e58bad148a35..6a9199e6c2c6 100644 --- a/drivers/virt/coco/tdx-host/Kconfig +++ b/drivers/virt/coco/tdx-host/Kconfig @@ -8,3 +8,13 @@ config TDX_HOST_SERVICES Say y or m if enabling support for confidential virtual machine support (CONFIG_INTEL_TDX_HOST). The module is called tdx_host.ko + +config INTEL_TDX_MODULE_UPDATE + bool "Intel TDX module runtime update" + depends on TDX_HOST_SERVICES + help + This enables the kernel to support TDX module runtime update. This + allows the admin to update the TDX module to another compatible + version without the need to terminate running TDX guests. + + If unsure, say N. -- 2.47.3