[PATCH v4 08/12] x86/tdx: Reimplement __tdx_hypercall() using TDX_MODULE_CALL asm

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

Now the TDX_HYPERCALL asm is basically identical to the TDX_MODULE_CALL
with both '\saved' and '\ret' enabled, with two minor things though:

1) The way to restore the structure pointer is different

The TDX_HYPERCALL uses RCX as spare to restore the structure pointer,
but the TDX_MODULE_CALL assumes no spare register can be used. In other
words, TDX_MODULE_CALL already covers what TDX_HYPERCALL does.

2) TDX_MODULE_CALL only clears shared registers for TDH.VP.ENTER

For this just need to make that code available for the non-host case.

Thus, remove the TDX_HYPERCALL and reimplement the __tdx_hypercall()
using the TDX_MODULE_CALL.

Extend the TDX_MODULE_CALL to cover "clear shared registers" for
TDG.VP.VMCALL. Introduce a new __tdcall_saved_ret() to replace the
temporary __tdcall_hypercall().

The __tdcall_saved_ret() can also be used for those new TDCALLs which
require more input/output registers than the basic TDCALLs do.

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>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---

v3 -> v4:
- Removed unneeded header file inclusion.
- Added Kirill's Reviewed-by tag.

v2 -> v3:
- No update

v1 -> v2:
- The second patch (new) split from v1 "x86/tdx: Unify TDX_HYPERCALL
and TDX_MODULE_CALL assembly"
- Rebase to 6.5-rc2.

---
arch/x86/coco/tdx/tdcall.S | 133 ++----------------------------
arch/x86/coco/tdx/tdx-shared.c | 4 +-
arch/x86/include/asm/shared/tdx.h | 2 +-
arch/x86/virt/vmx/tdx/tdxcall.S | 8 +-
4 files changed, 15 insertions(+), 132 deletions(-)

diff --git a/arch/x86/coco/tdx/tdcall.S b/arch/x86/coco/tdx/tdcall.S
index 6d76d7d49b72..52d9786da308 100644
--- a/arch/x86/coco/tdx/tdcall.S
+++ b/arch/x86/coco/tdx/tdcall.S
@@ -1,7 +1,6 @@
/* SPDX-License-Identifier: GPL-2.0 */
#include <asm/asm-offsets.h>
#include <asm/asm.h>
-#include <asm/frame.h>

#include <linux/linkage.h>
#include <linux/errno.h>
@@ -46,135 +45,19 @@ SYM_FUNC_START(__tdcall_ret)
SYM_FUNC_END(__tdcall_ret)

/*
- * TDX_HYPERCALL - Make hypercalls to a TDX VMM using TDVMCALL leaf of TDCALL
- * instruction
+ * __tdcall_saved_ret() - Used by TDX guests to request services from the
+ * TDX module (including VMM services) using TDCALL instruction, with
+ * saving output registers to the 'struct tdx_module_args' used as input.
*
- * Transforms values in function call argument struct tdx_module_args @args
- * into the TDCALL register ABI. After TDCALL operation, VMM output is saved
- * back in @args, if \ret is 1.
- *
- * Depends on the caller to pass TDG.VP.VMCALL as the TDCALL leaf, and set
- * @args::rcx to TDVMCALL_EXPOSE_REGS_MASK.
- *
- *-------------------------------------------------------------------------
- * TD VMCALL ABI:
- *-------------------------------------------------------------------------
- *
- * Input Registers:
- *
- * RAX - TDCALL instruction leaf number (0 - TDG.VP.VMCALL)
- * RCX - BITMAP which controls which part of TD Guest GPR
- * is passed as-is to the VMM and back.
- * R10 - Set 0 to indicate TDCALL follows standard TDX ABI
- * specification. Non zero value indicates vendor
- * specific ABI.
- * R11 - VMCALL sub function number
- * RBX, RDX, RDI, RSI - Used to pass VMCALL sub function specific arguments.
- * R8-R9, R12-R15 - Same as above.
- *
- * Output Registers:
- *
- * RAX - TDCALL instruction status (Not related to hypercall
- * output).
- * RBX, RDX, RDI, RSI - Hypercall sub function specific output values.
- * R8-R15 - Same as above.
- *
- */
-.macro TDX_HYPERCALL
- FRAME_BEGIN
-
- /* Save callee-saved GPRs as mandated by the x86_64 ABI */
- push %r15
- push %r14
- push %r13
- push %r12
- push %rbx
-
- /* Move Leaf ID to RAX */
- movq %rdi, %rax
-
- /* Move bitmap of shared registers to RCX */
- movq TDX_MODULE_rcx(%rsi), %rcx
-
- /* Copy hypercall registers from arg struct: */
- movq TDX_MODULE_r8(%rsi), %r8
- movq TDX_MODULE_r9(%rsi), %r9
- movq TDX_MODULE_r10(%rsi), %r10
- movq TDX_MODULE_r11(%rsi), %r11
- movq TDX_MODULE_r12(%rsi), %r12
- movq TDX_MODULE_r13(%rsi), %r13
- movq TDX_MODULE_r14(%rsi), %r14
- movq TDX_MODULE_r15(%rsi), %r15
- movq TDX_MODULE_rdi(%rsi), %rdi
- movq TDX_MODULE_rbx(%rsi), %rbx
- movq TDX_MODULE_rdx(%rsi), %rdx
-
- pushq %rsi
- movq TDX_MODULE_rsi(%rsi), %rsi
-
- tdcall
-
- /*
- * Restore the pointer of the structure to save output registers.
- *
- * RCX is used as bitmap of shared registers and doesn't hold any
- * value provided by the VMM, thus it can be used as spare to
- * restore the structure pointer.
- */
- popq %rcx
- movq %rsi, TDX_MODULE_rsi(%rcx)
- movq %rcx, %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)
- movq %r12, TDX_MODULE_r12(%rsi)
- movq %r13, TDX_MODULE_r13(%rsi)
- movq %r14, TDX_MODULE_r14(%rsi)
- movq %r15, TDX_MODULE_r15(%rsi)
- movq %rdi, TDX_MODULE_rdi(%rsi)
- movq %rbx, TDX_MODULE_rbx(%rsi)
- movq %rdx, TDX_MODULE_rdx(%rsi)
-
- /*
- * Zero out registers exposed to the VMM to avoid speculative execution
- * with VMM-controlled values. This needs to include all registers
- * present in TDVMCALL_EXPOSE_REGS_MASK, except RBX, and R12-R15 which
- * will be restored.
- */
- xor %r8d, %r8d
- xor %r9d, %r9d
- xor %r10d, %r10d
- xor %r11d, %r11d
- xor %rdi, %rdi
- xor %rsi, %rsi
- xor %rdx, %rdx
-
- /* Restore callee-saved GPRs as mandated by the x86_64 ABI */
- pop %rbx
- pop %r12
- pop %r13
- pop %r14
- pop %r15
-
- FRAME_END
-
- RET
-.endm
-
-/*
- *
- * __tdcall_hypercall() function ABI:
+ * __tdcall_saved_ret() function ABI:
*
* @fn (RDI) - TDCALL leaf ID, moved to RAX
* @args (RSI) - struct tdx_module_args for input/output
*
- * @fn and @args::rcx from the caller must be TDG_VP_VMCALL and
- * TDVMCALL_EXPOSE_REGS_MASK respectively.
+ * All registers in @args are used as input/output registers.
*
* On successful completion, return the hypercall error code.
*/
-SYM_FUNC_START(__tdcall_hypercall)
- TDX_HYPERCALL
-SYM_FUNC_END(__tdcall_hypercall)
+SYM_FUNC_START(__tdcall_saved_ret)
+ TDX_MODULE_CALL host=0 ret=1 saved=1
+SYM_FUNC_END(__tdcall_saved_ret)
diff --git a/arch/x86/coco/tdx/tdx-shared.c b/arch/x86/coco/tdx/tdx-shared.c
index b47c8cce91b0..344b3818f4c3 100644
--- a/arch/x86/coco/tdx/tdx-shared.c
+++ b/arch/x86/coco/tdx/tdx-shared.c
@@ -89,11 +89,11 @@ noinstr u64 __tdx_hypercall(struct tdx_hypercall_args *args)
};

/*
- * Failure of __tdcall_hypercall() indicates a failure of the TDVMCALL
+ * Failure of __tdcall_saved_ret() indicates a failure of the TDVMCALL
* mechanism itself and that something has gone horribly wrong with
* the TDX module. __tdx_hypercall_failed() never returns.
*/
- if (__tdcall_hypercall(TDG_VP_VMCALL, &margs))
+ if (__tdcall_saved_ret(TDG_VP_VMCALL, &margs))
__tdx_hypercall_failed();

args->r8 = margs.r8;
diff --git a/arch/x86/include/asm/shared/tdx.h b/arch/x86/include/asm/shared/tdx.h
index da5205daa53d..188e8bf3332c 100644
--- a/arch/x86/include/asm/shared/tdx.h
+++ b/arch/x86/include/asm/shared/tdx.h
@@ -81,6 +81,7 @@ struct tdx_module_args {
/* Used to communicate with the TDX module */
u64 __tdcall(u64 fn, struct tdx_module_args *args);
u64 __tdcall_ret(u64 fn, struct tdx_module_args *args);
+u64 __tdcall_saved_ret(u64 fn, struct tdx_module_args *args);

/*
* Used in __tdx_hypercall() to pass down and get back registers' values of
@@ -104,7 +105,6 @@ struct tdx_hypercall_args {
};

/* Used to request services from the VMM */
-u64 __tdcall_hypercall(u64 fn, struct tdx_module_args *args);
u64 __tdx_hypercall(struct tdx_hypercall_args *args);

/*
diff --git a/arch/x86/virt/vmx/tdx/tdxcall.S b/arch/x86/virt/vmx/tdx/tdxcall.S
index c54ea009b241..3f0b83a9977e 100644
--- a/arch/x86/virt/vmx/tdx/tdxcall.S
+++ b/arch/x86/virt/vmx/tdx/tdxcall.S
@@ -142,10 +142,10 @@
movq %r11, TDX_MODULE_r11(%rsi)
.endif /* \ret */

-.if \host && \saved && \ret
+.if \saved && \ret
/*
- * Clear registers shared by guest for VP.ENTER to prevent
- * speculative use of guest's values, including those are
+ * Clear registers shared by guest for VP.VMCALL/VP.ENTER to prevent
+ * speculative use of guest's/VMM's values, including those are
* restored from the stack.
*
* See arch/x86/kvm/vmx/vmenter.S:
@@ -170,7 +170,7 @@
xorl %r15d, %r15d
xorl %ebx, %ebx
xorl %edi, %edi
-.endif /* \host && \ret && \host */
+.endif /* \ret && \host */

.if \host
.Lout\@:
--
2.41.0