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x86/tdx: Reimplement __tdx_hypercall() using TDX_MODULE_CALL asm

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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: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Kai Huang <kai.huang@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/all/e68a2473fb6f5bcd78b078cae7510e9d0753b3df.1692096753.git.kai.huang%40intel.com
This commit is contained in:
Kai Huang 2023-08-15 23:02:02 +12:00 committed by Dave Hansen
parent c641cfb5c1
commit 90f5ecd37f
4 changed files with 15 additions and 132 deletions
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133
arch/x86/coco/tdx/tdcall.S
View file

@ -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)

4
arch/x86/coco/tdx/tdx-shared.c
View file

@ -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;

2
arch/x86/include/asm/shared/tdx.h
View file

@ -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);
/*

8
arch/x86/virt/vmx/tdx/tdxcall.S
View file

@ -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\@: