[PATCH v5 1/6] x86/virt/tdx: Move TDH.SYS.CONFIG operations into a wrapper

[Xu Yilun <yilun.xu@linux.intel.com>]

TDH.SYS.CONFIG is currently not wrapped in a SEAMCALL wrapper because it
is not exposed to external callers (such as KVM), also because the
level of TDX ABI details needed to perform the call is low enough to
flow well with the calling code.

But as more configurations are being added to this SEAMCALL leaf, more
ABI details are leaked into the surrounding caller code, which decreases
the readability of the caller logic. The first case is that the Dynamic
PAMT (DPAMT) change [1] tweaks the R8 argument based on whether DPAMT is
supported by the loaded TDX module.

A follow-up case comes as the TDX architecture has evolved the ABI to
introduce new leaf versions. The host must select the version to call
based on what new features are supported by the loaded TDX module.

Before the version selection makes the caller logic even messier, move
the register ABI operations into a wrapper.

The original changelog was written by hand. AI was used to help correct
grammatical errors and polish individual sentences for better
readability.

Signed-off-by: Xu Yilun <yilun.xu@linux.intel.com>
Link: https://lore.kernel.org/all/20260904215841.303070-10-rick.p.edgecombe@intel.com/ # [1]
---
v5:
 - Drop the tdmr_info_pa_array stuff (Dave)
 - Simplify the changelog (Dave)
 - Remove all Reviewed-by tags due to code change
 - Better clarify the AI usage

v4:
 - Cut the redundant opening words in the 1st paragraph (Rick)
 - Collect Reviewed-by tags

v3:
 - sizeof(tdmr_pa_array->phys[0]) instead of sizeof(u64) (Rick)
 - Re-phrase the code comments for struct tdmr_info_pa_array (Tony)
 - Refactor the changelog
 - Collect Reviewed-by tags

v2:
 - Remove TDH.SYS.UPDATE wrapper (Dave & Rick)
 - Talk about the handling of in-memory ABIs for SEAMCALL wrappers
   (Rick)
 - Refactor the entire changelog according to Rick's suggestion (Rick)
 - Add code comment for struct tdmr_info_pa_array (AI nitpicker)
 - Use kernel data type for nr_tdmr_pa parameter (AI nitpicker)

v1:
 - This patch is split out from the last series (Rick)
---
 arch/x86/virt/vmx/tdx/tdx.c | 30 +++++++++++++++++++-----------
 1 file changed, 19 insertions(+), 11 deletions(-)

diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index 96ced0494b68..c7bd0b01786d 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -1033,10 +1033,26 @@ static __init int construct_tdmrs(struct list_head *tmb_list,
 
 #define TDX_SYS_CONFIG_DYNAMIC_PAMT	BIT(16)
 
+static __init int tdx_sys_config(u64 *tdmr_pa_array, unsigned int nr_tdmr_pa,
+				 u64 global_keyid)
+{
+	struct tdx_module_args args = {
+		.rcx = __pa(tdmr_pa_array),
+		.rdx = nr_tdmr_pa,
+		.r8 = global_keyid,
+	};
+
+	if (tdx_supports_dynamic_pamt(&tdx_sysinfo)) {
+		pr_info("Enable Dynamic PAMT\n");
+		args.r8 |= TDX_SYS_CONFIG_DYNAMIC_PAMT;
+	}
+
+	return seamcall_prerr(TDH_SYS_CONFIG, &args);
+}
+
 static __init int config_tdx_module(struct tdmr_info_list *tdmr_list,
 				    u64 global_keyid)
 {
-	struct tdx_module_args args = {};
 	u64 *tdmr_pa_array;
 	size_t array_sz;
 	int i, ret;
@@ -1058,16 +1074,8 @@ static __init int config_tdx_module(struct tdmr_info_list *tdmr_list,
 	for (i = 0; i < tdmr_list->nr_consumed_tdmrs; i++)
 		tdmr_pa_array[i] = __pa(tdmr_entry(tdmr_list, i));
 
-	args.rcx = __pa(tdmr_pa_array);
-	args.rdx = tdmr_list->nr_consumed_tdmrs;
-	args.r8 = global_keyid;
-
-	if (tdx_supports_dynamic_pamt(&tdx_sysinfo)) {
-		pr_info("Enable Dynamic PAMT\n");
-		args.r8 |= TDX_SYS_CONFIG_DYNAMIC_PAMT;
-	}
-
-	ret = seamcall_prerr(TDH_SYS_CONFIG, &args);
+	ret = tdx_sys_config(tdmr_pa_array, tdmr_list->nr_consumed_tdmrs,
+			     global_keyid);
 
 	/* Free the array as it is not required anymore. */
 	kfree(tdmr_pa_array);

-- 
2.25.1