Re: [PATCH v2 3/5] x86/virt/tdx: Add SEAMCALL wrapper for TDH.SYS.DISABLE

[Kiryl Shutsemau <kas@kernel.org>]

On Mon, Mar 23, 2026 at 02:59:06PM -0600, Vishal Verma wrote:
> Some early TDX-capable platforms have an erratum where a partial write
> to TDX private memory can cause a machine check on a subsequent read.
> On these platforms, kexec and kdump have been disabled in these cases,
> because the old kernel cannot safely hand off TDX state to the new
> kernel. Later TDX modules support the TDH.SYS.DISABLE SEAMCALL, which
> provides a way to cleanly disable TDX and allow kexec to proceed.
> 
> The new SEAMCALL has an enumeration bit, but that is ignored. It is
> expected that users will be using the latest TDX module, and the failure
> mode for running the missing SEAMCALL on an older module is not fatal.
> 
> This can be a long running operation, and the time needed largely
> depends on the amount of memory that has been allocated to TDs. If all
> TDs have been destroyed prior to the sys_disable call, then it is fast,
> with only needing to override the TDX module memory.
> 
> After the SEAMCALL completes, the TDX module is disabled and all memory
> resources allocated to TDX are freed and reset. The next kernel can then
> re-initialize the TDX module from scratch via the normal TDX bring-up
> sequence.
> 
> The SEAMCALL can return two different error codes that expect a retry.
>  - TDX_INTERRUPTED_RESUMABLE can be returned in the case of a host
>    interrupt. However, it will not return until it makes some forward
>    progress, so we can expect to complete even in the case of interrupt
>    storms.
>  - TDX_SYS_BUSY will be returned on contention with other TDH.SYS.*
>    SEAMCALLs, however a side effect of TDH.SYS.DISABLE is that it will
>    block other SEAMCALLs once it gets going. So this contention will be
>    short lived.
> 
> So loop infinitely on either of these error codes, until success or other
> error.
> 
> Co-developed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
> ---
>  arch/x86/include/asm/shared/tdx_errno.h |  1 +
>  arch/x86/include/asm/tdx.h              |  3 +++
>  arch/x86/virt/vmx/tdx/tdx.h             |  1 +
>  arch/x86/virt/vmx/tdx/tdx.c             | 28 ++++++++++++++++++++++++++++
>  4 files changed, 33 insertions(+)
> 
> diff --git a/arch/x86/include/asm/shared/tdx_errno.h b/arch/x86/include/asm/shared/tdx_errno.h
> index 8bf6765cf082..246b4fd54a48 100644
> --- a/arch/x86/include/asm/shared/tdx_errno.h
> +++ b/arch/x86/include/asm/shared/tdx_errno.h
> @@ -15,6 +15,7 @@
>  #define TDX_NON_RECOVERABLE_TD_NON_ACCESSIBLE	0x6000000500000000ULL
>  #define TDX_NON_RECOVERABLE_TD_WRONG_APIC_MODE	0x6000000700000000ULL
>  #define TDX_INTERRUPTED_RESUMABLE		0x8000000300000000ULL
> +#define TDX_SYS_BUSY				0x8000020200000000ULL
>  #define TDX_OPERAND_INVALID			0xC000010000000000ULL
>  #define TDX_OPERAND_BUSY			0x8000020000000000ULL
>  #define TDX_PREVIOUS_TLB_EPOCH_BUSY		0x8000020100000000ULL
> diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> index 7674fc530090..a0a4a15142fc 100644
> --- a/arch/x86/include/asm/tdx.h
> +++ b/arch/x86/include/asm/tdx.h
> @@ -172,6 +172,8 @@ static inline int pg_level_to_tdx_sept_level(enum pg_level level)
>          return level - 1;
>  }
>  
> +void tdx_sys_disable(void);
> +
>  u64 tdh_vp_enter(struct tdx_vp *vp, struct tdx_module_args *args);
>  u64 tdh_mng_addcx(struct tdx_td *td, struct page *tdcs_page);
>  u64 tdh_mem_page_add(struct tdx_td *td, u64 gpa, struct page *page, struct page *source, u64 *ext_err1, u64 *ext_err2);
> @@ -203,6 +205,7 @@ static inline void tdx_init(void) { }
>  static inline u32 tdx_get_nr_guest_keyids(void) { return 0; }
>  static inline const char *tdx_dump_mce_info(struct mce *m) { return NULL; }
>  static inline const struct tdx_sys_info *tdx_get_sysinfo(void) { return NULL; }
> +static inline void tdx_sys_disable(void) { }
>  #endif	/* CONFIG_INTEL_TDX_HOST */
>  
>  #endif /* !__ASSEMBLER__ */
> diff --git a/arch/x86/virt/vmx/tdx/tdx.h b/arch/x86/virt/vmx/tdx/tdx.h
> index dde219c823b4..e2cf2dd48755 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.h
> +++ b/arch/x86/virt/vmx/tdx/tdx.h
> @@ -46,6 +46,7 @@
>  #define TDH_PHYMEM_PAGE_WBINVD		41
>  #define TDH_VP_WR			43
>  #define TDH_SYS_CONFIG			45
> +#define TDH_SYS_DISABLE			69
>  
>  /*
>   * SEAMCALL leaf:
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index 0802d0fd18a4..3a76000dec7a 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -37,6 +37,7 @@
>  #include <asm/msr.h>
>  #include <asm/cpufeature.h>
>  #include <asm/tdx.h>
> +#include <asm/shared/tdx_errno.h>
>  #include <asm/cpu_device_id.h>
>  #include <asm/processor.h>
>  #include <asm/mce.h>
> @@ -1940,3 +1941,30 @@ u64 tdh_phymem_page_wbinvd_hkid(u64 hkid, struct page *page)
>  	return seamcall(TDH_PHYMEM_PAGE_WBINVD, &args);
>  }
>  EXPORT_SYMBOL_FOR_KVM(tdh_phymem_page_wbinvd_hkid);
> +
> +void tdx_sys_disable(void)
> +{
> +	struct tdx_module_args args = {};
> +	u64 ret;
> +
> +	/*
> +	 * Don't loop forever.

Nit: Add a new line here.

> +	 *  - TDX_INTERRUPTED_RESUMABLE guarantees forward progress between
> +	 *    calls.

And here.

> +	 *  - TDX_SYS_BUSY could transiently contend with TDH.SYS.* SEAMCALLs,
> +	 *    but will lock out future ones.

Locked out by who? Is it TDX module contract? I don't see it documented in
the spec.

I assumed that if the SEAMCALL fails other SEAMCALLs suppose to be
functional. Hm?

> +	 *
> +	 * This is a 'destructive' SEAMCALL, in that no other SEAMCALL can be
> +	 * run after this until a full reinitialization is done.
> +	 */
> +	do {
> +		ret = seamcall(TDH_SYS_DISABLE, &args);
> +	} while (ret == TDX_INTERRUPTED_RESUMABLE || ret == TDX_SYS_BUSY);
> +
> +	/*
> +	 * Print SEAMCALL failures, but not SW-defined error codes
> +	 * (SEAMCALL faulted with #GP/#UD, TDX not supported).
> +	 */
> +	if (ret && (ret & TDX_SW_ERROR) != TDX_SW_ERROR)
> +		pr_err("TDH.SYS.DISABLE failed: 0x%016llx\n", ret);
> +}
> 
> -- 
> 2.53.0
> 

-- 
  Kiryl Shutsemau / Kirill A. Shutemov