Commit 90f5ecd3 authored by Kai Huang's avatar Kai Huang Committed by Dave Hansen
Browse files

x86/tdx: Reimplement __tdx_hypercall() using TDX_MODULE_CALL asm 



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.

Suggested-by: default avatarPeter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarKai Huang <kai.huang@intel.com>
Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/all/e68a2473fb6f5bcd78b078cae7510e9d0753b3df.1692096753.git.kai.huang%40intel.com
parent c641cfb5

arch/x86/coco/tdx/tdcall.S

+8 −125
Original line number Diff line number Diff line 
/* 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

 *

 * 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_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.

 *

 * __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)

arch/x86/coco/tdx/tdx-shared.c

+2 −2
Original line number Diff line number Diff line
@@ -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;

arch/x86/include/asm/shared/tdx.h

+1 −1
Original line number Diff line number Diff line
@@ -83,6 +83,7 @@ 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
@@ -106,7 +107,6 @@ 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);



/*

arch/x86/virt/vmx/tdx/tdxcall.S

+4 −4
Original line number Diff line number Diff line
@@ -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\@: