[PATCH v4 05/12] x86/tdx: Pass TDCALL/SEAMCALL input/output registers via a structure

Kai Huang
2023-08-15T11:03:28Z

Currently, the TDX_MODULE_CALL asm macro, which handles both TDCALL and
SEAMCALL, takes one parameter for each input register and an optional
'struct tdx_module_output' (a collection of output registers) as output.
This is different from the TDX_HYPERCALL macro which uses a single
'struct tdx_hypercall_args' to carry all input/output registers.

The newer TDX versions introduce more TDCALLs/SEAMCALLs which use more
input/output registers. Also, the TDH.VP.ENTER (which isn't covered
by the current TDX_MODULE_CALL macro) basically can use all registers
that the TDX_HYPERCALL does. The current TDX_MODULE_CALL macro isn't
extendible to cover those cases.

Similar to the TDX_HYPERCALL macro, simplify the TDX_MODULE_CALL macro
to use a single structure 'struct tdx_module_args' to carry all the
input/output registers. Currently, R10/R11 are only used as output
register but not as input by any TDCALL/SEAMCALL. Change to also use
R10/R11 as input register to make input/output registers symmetric.

Currently, the TDX_MODULE_CALL macro depends on the caller to pass a
non-NULL 'struct tdx_module_output' to get additional output registers.
Similar to the TDX_HYPERCALL macro, change the TDX_MODULE_CALL macro to
take a new 'ret' macro argument to indicate whether to save the output
registers to the 'struct tdx_module_args'. Also introduce a new
__tdcall_ret() for that purpose, similar to the __tdx_hypercall_ret().

Note the tdcall(), which is a wrapper of __tdcall(), is called by three
callers: tdx_parse_tdinfo(), tdx_get_ve_info() and tdx_early_init().
The former two need the additional output but the last one doesn't. For
simplicity, make tdcall() always call __tdcall_ret() to avoid another
"_ret()" wrapper. The last caller tdx_early_init() isn't performance
critical anyway.

Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Kai Huang <kai.huang@intel.com>
---

v3 -> v4:
- Also use R10/R11 as input registers. - Kirill

v2 -> v3:
- No change.

v1 -> v2:
- Code change due to patch 02.
- Minor improvement in comments and changelog.

---
arch/x86/coco/tdx/tdcall.S | 47 ++++++---------
arch/x86/coco/tdx/tdx-shared.c | 6 +-
arch/x86/coco/tdx/tdx.c | 44 ++++++++------
arch/x86/include/asm/shared/tdx.h | 8 +--
arch/x86/kernel/asm-offsets.c | 12 ++--
arch/x86/virt/vmx/tdx/tdxcall.S | 97 +++++++++++++------------------
6 files changed, 96 insertions(+), 118 deletions(-)

diff --git a/arch/x86/coco/tdx/tdcall.S b/arch/x86/coco/tdx/tdcall.S
index 6aebac08f2bf..56b9cd32895e 100644
--- a/arch/x86/coco/tdx/tdcall.S
+++ b/arch/x86/coco/tdx/tdcall.S
@@ -43,37 +43,10 @@
* __tdcall() - Used by TDX guests to request services from the TDX
* module (does not include VMM services) using TDCALL instruction.
*
- * Transforms function call register arguments into the TDCALL register ABI.
- * After TDCALL operation, TDX module output is saved in @out (if it is
- * provided by the user).
- *
- *-------------------------------------------------------------------------
- * TDCALL ABI:
- *-------------------------------------------------------------------------
- * Input Registers:
- *
- * RAX - TDCALL Leaf number.
- * RCX,RDX,R8-R9 - TDCALL Leaf specific input registers.
- *
- * Output Registers:
- *
- * RAX - TDCALL instruction error code.
- * RCX,RDX,R8-R11 - TDCALL Leaf specific output registers.
- *
- *-------------------------------------------------------------------------
- *
* __tdcall() function ABI:
*
- * @fn (RDI) - TDCALL Leaf ID, moved to RAX
- * @rcx (RSI) - Input parameter 1, moved to RCX
- * @rdx (RDX) - Input parameter 2, moved to RDX
- * @r8 (RCX) - Input parameter 3, moved to R8
- * @r9 (R8) - Input parameter 4, moved to R9
- *
- * @out (R9) - struct tdx_module_output pointer
- * stored temporarily in R12 (not
- * shared with the TDX module). It
- * can be NULL.
+ * @fn (RDI) - TDCALL Leaf ID, moved to RAX
+ * @args (RSI) - struct tdx_module_args for input
*
* Return status of TDCALL via RAX.
*/
@@ -81,6 +54,22 @@ SYM_FUNC_START(__tdcall)
TDX_MODULE_CALL host=0
SYM_FUNC_END(__tdcall)

+/*
+ * __tdcall_ret() - Used by TDX guests to request services from the TDX
+ * module (does not include VMM services) using TDCALL instruction, with
+ * saving output registers to the 'struct tdx_module_args' used as input.
+ *
+ * __tdcall_ret() function ABI:
+ *
+ * @fn (RDI) - TDCALL Leaf ID, moved to RAX
+ * @args (RSI) - struct tdx_module_args for input and output
+ *
+ * Return status of TDCALL via RAX.
+ */
+SYM_FUNC_START(__tdcall_ret)
+ TDX_MODULE_CALL host=0 ret=1
+SYM_FUNC_END(__tdcall_ret)
+
/*
* TDX_HYPERCALL - Make hypercalls to a TDX VMM using TDVMCALL leaf of TDCALL
* instruction
diff --git a/arch/x86/coco/tdx/tdx-shared.c b/arch/x86/coco/tdx/tdx-shared.c
index 90631abdac34..a7396d0ddef9 100644
--- a/arch/x86/coco/tdx/tdx-shared.c
+++ b/arch/x86/coco/tdx/tdx-shared.c
@@ -5,7 +5,7 @@ static unsigned long try_accept_one(phys_addr_t start, unsigned long len,
enum pg_level pg_level)
{
unsigned long accept_size = page_level_size(pg_level);
- u64 tdcall_rcx;
+ struct tdx_module_args args = {};
u8 page_size;

if (!IS_ALIGNED(start, accept_size))
@@ -34,8 +34,8 @@ static unsigned long try_accept_one(phys_addr_t start, unsigned long len,
return 0;
}

- tdcall_rcx = start | page_size;
- if (__tdcall(TDG_MEM_PAGE_ACCEPT, tdcall_rcx, 0, 0, 0, NULL))
+ args.rcx = start | page_size;
+ if (__tdcall(TDG_MEM_PAGE_ACCEPT, &args))
return 0;

return accept_size;
diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 8c13944925e3..2e19cc62e59e 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -66,10 +66,9 @@ EXPORT_SYMBOL_GPL(tdx_kvm_hypercall);
* should only be used for calls that have no legitimate reason to fail
* or where the kernel can not survive the call failing.
*/
-static inline void tdcall(u64 fn, u64 rcx, u64 rdx, u64 r8, u64 r9,
- struct tdx_module_output *out)
+static inline void tdcall(u64 fn, struct tdx_module_args *args)
{
- if (__tdcall(fn, rcx, rdx, r8, r9, out))
+ if (__tdcall_ret(fn, args))
panic("TDCALL %lld failed (Buggy TDX module!)\n", fn);
}

@@ -89,11 +88,14 @@ static inline void tdcall(u64 fn, u64 rcx, u64 rdx, u64 r8, u64 r9,
*/
int tdx_mcall_get_report0(u8 *reportdata, u8 *tdreport)
{
+ struct tdx_module_args args = {
+ .rcx = virt_to_phys(tdreport),
+ .rdx = virt_to_phys(reportdata),
+ .r8 = TDREPORT_SUBTYPE_0,
+ };
u64 ret;

- ret = __tdcall(TDG_MR_REPORT, virt_to_phys(tdreport),
- virt_to_phys(reportdata), TDREPORT_SUBTYPE_0,
- 0, NULL);
+ ret = __tdcall(TDG_MR_REPORT, &args);
if (ret) {
if (TDCALL_RETURN_CODE(ret) == TDCALL_INVALID_OPERAND)
return -EINVAL;
@@ -141,7 +143,7 @@ static void __noreturn tdx_panic(const char *msg)

static void tdx_parse_tdinfo(u64 *cc_mask)
{
- struct tdx_module_output out;
+ struct tdx_module_args args = {};
unsigned int gpa_width;
u64 td_attr;

@@ -152,7 +154,7 @@ static void tdx_parse_tdinfo(u64 *cc_mask)
* Guest-Host-Communication Interface (GHCI), section 2.4.2 TDCALL
* [TDG.VP.INFO].
*/
- tdcall(TDG_VP_INFO, 0, 0, 0, 0, &out);
+ tdcall(TDG_VP_INFO, &args);

/*
* The highest bit of a guest physical address is the "sharing" bit.
@@ -161,7 +163,7 @@ static void tdx_parse_tdinfo(u64 *cc_mask)
* The GPA width that comes out of this call is critical. TDX guests
* can not meaningfully run without it.
*/
- gpa_width = out.rcx & GENMASK(5, 0);
+ gpa_width = args.rcx & GENMASK(5, 0);
*cc_mask = BIT_ULL(gpa_width - 1);

/*
@@ -169,7 +171,7 @@ static void tdx_parse_tdinfo(u64 *cc_mask)
* memory. Ensure that no #VE will be delivered for accesses to
* TD-private memory. Only VMM-shared memory (MMIO) will #VE.
*/
- td_attr = out.rdx;
+ td_attr = args.rdx;
if (!(td_attr & ATTR_SEPT_VE_DISABLE)) {
const char *msg = "TD misconfiguration: SEPT_VE_DISABLE attribute must be set.";

@@ -577,7 +579,7 @@ __init bool tdx_early_handle_ve(struct pt_regs *regs)

void tdx_get_ve_info(struct ve_info *ve)
{
- struct tdx_module_output out;
+ struct tdx_module_args args = {};

/*
* Called during #VE handling to retrieve the #VE info from the
@@ -594,15 +596,15 @@ void tdx_get_ve_info(struct ve_info *ve)
* Note, the TDX module treats virtual NMIs as inhibited if the #VE
* valid flag is set. It means that NMI=>#VE will not result in a #DF.
*/
- tdcall(TDG_VP_VEINFO_GET, 0, 0, 0, 0, &out);
+ tdcall(TDG_VP_VEINFO_GET, &args);

/* Transfer the output parameters */
- ve->exit_reason = out.rcx;
- ve->exit_qual = out.rdx;
- ve->gla = out.r8;
- ve->gpa = out.r9;
- ve->instr_len = lower_32_bits(out.r10);
- ve->instr_info = upper_32_bits(out.r10);
+ ve->exit_reason = args.rcx;
+ ve->exit_qual = args.rdx;
+ ve->gla = args.r8;
+ ve->gpa = args.r9;
+ ve->instr_len = lower_32_bits(args.r10);
+ ve->instr_info = upper_32_bits(args.r10);
}

/*
@@ -759,6 +761,10 @@ static bool tdx_enc_status_change_finish(unsigned long vaddr, int numpages,

void __init tdx_early_init(void)
{
+ struct tdx_module_args args = {
+ .rdx = TDCS_NOTIFY_ENABLES,
+ .r9 = -1ULL,
+ };
u64 cc_mask;
u32 eax, sig[3];

@@ -774,7 +780,7 @@ void __init tdx_early_init(void)
cc_set_mask(cc_mask);

/* Kernel does not use NOTIFY_ENABLES and does not need random #VEs */
- tdcall(TDG_VM_WR, 0, TDCS_NOTIFY_ENABLES, 0, -1ULL, NULL);
+ tdcall(TDG_VM_WR, &args);

/*
* All bits above GPA width are reserved and kernel treats shared bit
diff --git a/arch/x86/include/asm/shared/tdx.h b/arch/x86/include/asm/shared/tdx.h
index 9e3699b751ef..3606463ebf6f 100644
--- a/arch/x86/include/asm/shared/tdx.h
+++ b/arch/x86/include/asm/shared/tdx.h
@@ -74,11 +74,11 @@ static inline u64 _tdx_hypercall(u64 fn, u64 r12, u64 r13, u64 r14, u64 r15)
void __tdx_hypercall_failed(void);

/*
- * Used in __tdx_module_call() to gather the output registers' values of the
+ * Used in __tdcall*() to gather the input/output registers' values of the
* TDCALL instruction when requesting services from the TDX module. This is a
* software only structure and not part of the TDX module/VMM ABI
*/
-struct tdx_module_output {
+struct tdx_module_args {
u64 rcx;
u64 rdx;
u64 r8;
@@ -88,8 +88,8 @@ struct tdx_module_output {
};

/* Used to communicate with the TDX module */
-u64 __tdcall(u64 fn, u64 rcx, u64 rdx, u64 r8, u64 r9,
- struct tdx_module_output *out);
+u64 __tdcall(u64 fn, struct tdx_module_args *args);
+u64 __tdcall_ret(u64 fn, struct tdx_module_args *args);

bool tdx_accept_memory(phys_addr_t start, phys_addr_t end);

diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
index dc3576303f1a..50383bc46dd7 100644
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -68,12 +68,12 @@ static void __used common(void)
#endif

BLANK();
- OFFSET(TDX_MODULE_rcx, tdx_module_output, rcx);
- OFFSET(TDX_MODULE_rdx, tdx_module_output, rdx);
- OFFSET(TDX_MODULE_r8, tdx_module_output, r8);
- OFFSET(TDX_MODULE_r9, tdx_module_output, r9);
- OFFSET(TDX_MODULE_r10, tdx_module_output, r10);
- OFFSET(TDX_MODULE_r11, tdx_module_output, r11);
+ OFFSET(TDX_MODULE_rcx, tdx_module_args, rcx);
+ OFFSET(TDX_MODULE_rdx, tdx_module_args, rdx);
+ OFFSET(TDX_MODULE_r8, tdx_module_args, r8);
+ OFFSET(TDX_MODULE_r9, tdx_module_args, r9);
+ OFFSET(TDX_MODULE_r10, tdx_module_args, r10);
+ OFFSET(TDX_MODULE_r11, tdx_module_args, r11);

BLANK();
OFFSET(TDX_HYPERCALL_r8, tdx_hypercall_args, r8);
diff --git a/arch/x86/virt/vmx/tdx/tdxcall.S b/arch/x86/virt/vmx/tdx/tdxcall.S
index 6bdf6e137953..e9e19e7d77f8 100644
--- a/arch/x86/virt/vmx/tdx/tdxcall.S
+++ b/arch/x86/virt/vmx/tdx/tdxcall.S
@@ -17,34 +17,35 @@
* TDX module and hypercalls to the VMM.
* SEAMCALL - used by TDX hosts to make requests to the
* TDX module.
+ *
+ *-------------------------------------------------------------------------
+ * TDCALL/SEAMCALL ABI:
+ *-------------------------------------------------------------------------
+ * Input Registers:
+ *
+ * RAX - TDCALL/SEAMCALL Leaf number.
+ * RCX,RDX,R8-R11 - TDCALL/SEAMCALL Leaf specific input registers.
+ *
+ * Output Registers:
+ *
+ * RAX - TDCALL/SEAMCALL instruction error code.
+ * RCX,RDX,R8-R11 - TDCALL/SEAMCALL Leaf specific output registers.
+ *
+ *-------------------------------------------------------------------------
*/
-.macro TDX_MODULE_CALL host:req
+.macro TDX_MODULE_CALL host:req ret=0
FRAME_BEGIN
- /*
- * R12 will be used as temporary storage for struct tdx_module_output
- * pointer. Since R12-R15 registers are not used by TDCALL/SEAMCALL
- * services supported by this function, it can be reused.
- */

- /* Callee saved, so preserve it */
- push %r12
-
- /*
- * Push output pointer to stack.
- * After the operation, it will be fetched into R12 register.
- */
- push %r9
-
- /* Mangle function call ABI into TDCALL/SEAMCALL ABI: */
/* Move Leaf ID to RAX */
mov %rdi, %rax
- /* Move input 4 to R9 */
- mov %r8, %r9
- /* Move input 3 to R8 */
- mov %rcx, %r8
- /* Move input 1 to RCX */
- mov %rsi, %rcx
- /* Leave input param 2 in RDX */
+
+ /* Move other input regs from 'struct tdx_module_args' */
+ movq TDX_MODULE_rcx(%rsi), %rcx
+ movq TDX_MODULE_rdx(%rsi), %rdx
+ movq TDX_MODULE_r8(%rsi), %r8
+ movq TDX_MODULE_r9(%rsi), %r9
+ movq TDX_MODULE_r10(%rsi), %r10
+ movq TDX_MODULE_r11(%rsi), %r11

.if \host
seamcall
@@ -59,49 +60,31 @@
* This value will never be used as actual SEAMCALL error code as
* it is from the Reserved status code class.
*/
- jc .Lseamcall_vmfailinvalid
+ jc .Lseamcall_vmfailinvalid\@
.else
tdcall
.endif

- /*
- * Fetch output pointer from stack to R12 (It is used
- * as temporary storage)
- */
- pop %r12
-
- /*
- * Since this macro can be invoked with NULL as an output pointer,
- * check if caller provided an output struct before storing output
- * registers.
- *
- * Update output registers, even if the call failed (RAX != 0).
- * Other registers may contain details of the failure.
- */
- test %r12, %r12
- jz .Lout
-
- /* Copy result registers to output struct: */
- movq %rcx, TDX_MODULE_rcx(%r12)
- movq %rdx, TDX_MODULE_rdx(%r12)
- movq %r8, TDX_MODULE_r8(%r12)
- movq %r9, TDX_MODULE_r9(%r12)
- movq %r10, TDX_MODULE_r10(%r12)
- movq %r11, TDX_MODULE_r11(%r12)
-
-.Lout:
- /* Restore the state of R12 register */
- pop %r12
-
+.if \ret
+ /* Copy output registers to the structure */
+ movq %rcx, TDX_MODULE_rcx(%rsi)
+ movq %rdx, TDX_MODULE_rdx(%rsi)
+ movq %r8, TDX_MODULE_r8(%rsi)
+ movq %r9, TDX_MODULE_r9(%rsi)
+ movq %r10, TDX_MODULE_r10(%rsi)
+ movq %r11, TDX_MODULE_r11(%rsi)
+.endif
+
+.if \host
+.Lout\@:
+.endif
FRAME_END
RET

.if \host
-.Lseamcall_vmfailinvalid:
+.Lseamcall_vmfailinvalid\@:
mov $TDX_SEAMCALL_VMFAILINVALID, %rax
- /* pop the unused output pointer back to %r9 */
- pop %r9
- jmp .Lout
+ jmp .Lout\@
.endif /* \host */

.endm
--
2.41.0