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Peter Anvin" Subject: [PATCH v4 24/24] [NOT-FOR-REVIEW] x86/virt/seamldr: Save and restore current VMCS Date: Thu, 12 Feb 2026 06:35:27 -0800 Message-ID: <20260212143606.534586-25-chao.gao@intel.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260212143606.534586-1-chao.gao@intel.com> References: <20260212143606.534586-1-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 P-SEAMLDR calls clobber 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. Save and restore the current VMCS using VMPTRST and VMPTRLD instructions to avoid breaking KVM. Signed-off-by: Chao Gao --- This patch is needed for testing until microcode is updated to preserve the current VMCS across P-SEAMLDR calls. Otherwise, if some normal VMs are running before TDX Module updates, vmread/vmwrite errors may occur immediately after updates. --- arch/x86/include/asm/special_insns.h | 22 ++++++++++++++++++++++ arch/x86/virt/vmx/tdx/seamldr.c | 16 +++++++++++++++- 2 files changed, 37 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h index 46aa2c9c1bda..a3e9a139b669 100644 --- a/arch/x86/include/asm/special_insns.h +++ b/arch/x86/include/asm/special_insns.h @@ -303,6 +303,28 @@ static __always_inline void tile_release(void) asm volatile(".byte 0xc4, 0xe2, 0x78, 0x49, 0xc0"); } +static inline int vmptrst(u64 *vmcs_pa) +{ + asm goto("1: vmptrst %0\n\t" + _ASM_EXTABLE(1b, %l[error]) + : "=m" (*vmcs_pa) : : "cc" : error); + + return 0; +error: + return -EIO; +} + +static inline int vmptrld(u64 vmcs_pa) +{ + asm goto("1: vmptrld %0\n\t" + "jna %l[error]\n\t" + _ASM_EXTABLE(1b, %l[error]) + : : "m" (vmcs_pa) : "cc" : error); + return 0; +error: + return -EIO; +} + #endif /* __KERNEL__ */ #endif /* _ASM_X86_SPECIAL_INSNS_H */ diff --git a/arch/x86/virt/vmx/tdx/seamldr.c b/arch/x86/virt/vmx/tdx/seamldr.c index 3f37cc6c68ff..02695307b8a0 100644 --- a/arch/x86/virt/vmx/tdx/seamldr.c +++ b/arch/x86/virt/vmx/tdx/seamldr.c @@ -16,6 +16,7 @@ #include #include +#include #include "seamcall_internal.h" #include "tdx.h" @@ -59,12 +60,25 @@ static DEFINE_RAW_SPINLOCK(seamldr_lock); static int seamldr_call(u64 fn, struct tdx_module_args *args) { + u64 current_vmcs = -1ULL; + int ret; + /* * Serialize P-SEAMLDR calls and disable interrupts as the calls * can be made from IRQ context. */ guard(raw_spinlock_irqsave)(&seamldr_lock); - return seamcall_prerr(fn, args); + + /* + * P-SEAMLDR calls clobber the current VMCS. Save and restore it. + * -1 indicates invalid VMCS and no restoration is needed. + */ + WARN_ON_ONCE(vmptrst(¤t_vmcs)); + ret = seamcall_prerr(fn, args); + if (current_vmcs != -1ULL) + WARN_ON_ONCE(vmptrld(current_vmcs)); + + return ret; } int seamldr_get_info(struct seamldr_info *seamldr_info) -- 2.47.3