[PATCH v2 4/6] x86/tdx: Expand __tdx_hypercall() to handle more arguments

From: Dexuan Cui
Date: Tue Dec 06 2022 - 19:35:54 EST

From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>

So far __tdx_hypercall() only handles six arguments for VMCALL.
Expanding it to six more register would allow to cover more use-cases.

Using RDI and RSI as VMCALL arguments requires more register shuffling.
RAX is used to hold tdx_hypercall_args pointer and RBP stores flags.

While there, fix typo in the comment on panic branch.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reviewed-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
Tested-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
---

This patch is from Kirill. I'm posting the patch on behalf him:
https://lwn.net/ml/linux-kernel/20221202214741.7vfmqgvgubxqffen@xxxxxxxxxxxxxxxxx/

This is actually v1, but let's use v2 in the Subject to be consistent
with the Subjects of the other patches.

arch/x86/coco/tdx/tdcall.S | 82 ++++++++++++++++++++++---------
arch/x86/include/asm/shared/tdx.h | 6 +++
arch/x86/kernel/asm-offsets.c | 6 +++
3 files changed, 70 insertions(+), 24 deletions(-)

diff --git a/arch/x86/coco/tdx/tdcall.S b/arch/x86/coco/tdx/tdcall.S
index f9eb1134f22d..64e57739dc9d 100644
--- a/arch/x86/coco/tdx/tdcall.S
+++ b/arch/x86/coco/tdx/tdcall.S
@@ -13,6 +13,12 @@
/*
* Bitmasks of exposed registers (with VMM).
*/
+#define TDX_RDX BIT(2)
+#define TDX_RBX BIT(3)
+#define TDX_RSI BIT(6)
+#define TDX_RDI BIT(7)
+#define TDX_R8 BIT(8)
+#define TDX_R9 BIT(9)
#define TDX_R10 BIT(10)
#define TDX_R11 BIT(11)
#define TDX_R12 BIT(12)
@@ -27,9 +33,9 @@
* details can be found in TDX GHCI specification, section
* titled "TDCALL [TDG.VP.VMCALL] leaf".
*/
-#define TDVMCALL_EXPOSE_REGS_MASK ( TDX_R10 | TDX_R11 | \
- TDX_R12 | TDX_R13 | \
- TDX_R14 | TDX_R15 )
+#define TDVMCALL_EXPOSE_REGS_MASK \
+ ( TDX_RDX | TDX_RBX | TDX_RSI | TDX_RDI | TDX_R8 | TDX_R9 | \
+ TDX_R10 | TDX_R11 | TDX_R12 | TDX_R13 | TDX_R14 | TDX_R15 )

/*
* __tdx_module_call() - Used by TDX guests to request services from
@@ -124,19 +130,32 @@ SYM_FUNC_START(__tdx_hypercall)
push %r14
push %r13
push %r12
+ push %rbx
+ push %rbp
+
+ movq %rdi, %rax
+ movq %rsi, %rbp
+
+ /* Copy hypercall registers from arg struct: */
+ movq TDX_HYPERCALL_r8(%rax), %r8
+ movq TDX_HYPERCALL_r9(%rax), %r9
+ movq TDX_HYPERCALL_r10(%rax), %r10
+ movq TDX_HYPERCALL_r11(%rax), %r11
+ movq TDX_HYPERCALL_r12(%rax), %r12
+ movq TDX_HYPERCALL_r13(%rax), %r13
+ movq TDX_HYPERCALL_r14(%rax), %r14
+ movq TDX_HYPERCALL_r15(%rax), %r15
+ movq TDX_HYPERCALL_rdi(%rax), %rdi
+ movq TDX_HYPERCALL_rsi(%rax), %rsi
+ movq TDX_HYPERCALL_rbx(%rax), %rbx
+ movq TDX_HYPERCALL_rdx(%rax), %rdx
+
+ push %rax

/* Mangle function call ABI into TDCALL ABI: */
/* Set TDCALL leaf ID (TDVMCALL (0)) in RAX */
xor %eax, %eax

- /* Copy hypercall registers from arg struct: */
- movq TDX_HYPERCALL_r10(%rdi), %r10
- movq TDX_HYPERCALL_r11(%rdi), %r11
- movq TDX_HYPERCALL_r12(%rdi), %r12
- movq TDX_HYPERCALL_r13(%rdi), %r13
- movq TDX_HYPERCALL_r14(%rdi), %r14
- movq TDX_HYPERCALL_r15(%rdi), %r15
-
movl $TDVMCALL_EXPOSE_REGS_MASK, %ecx

/*
@@ -148,14 +167,14 @@ SYM_FUNC_START(__tdx_hypercall)
* HLT operation indefinitely. Since this is the not the desired
* result, conditionally call STI before TDCALL.
*/
- testq $TDX_HCALL_ISSUE_STI, %rsi
+ testq $TDX_HCALL_ISSUE_STI, %rbp
jz .Lskip_sti
sti
.Lskip_sti:
tdcall

/*
- * RAX==0 indicates a failure of the TDVMCALL mechanism itself and that
+ * RAX!=0 indicates a failure of the TDVMCALL mechanism itself and that
* something has gone horribly wrong with the TDX module.
*
* The return status of the hypercall operation is in a separate
@@ -165,30 +184,45 @@ SYM_FUNC_START(__tdx_hypercall)
testq %rax, %rax
jne .Lpanic

- /* TDVMCALL leaf return code is in R10 */
- movq %r10, %rax
+ pop %rax

/* Copy hypercall result registers to arg struct if needed */
- testq $TDX_HCALL_HAS_OUTPUT, %rsi
+ testq $TDX_HCALL_HAS_OUTPUT, %rbp
jz .Lout

- movq %r10, TDX_HYPERCALL_r10(%rdi)
- movq %r11, TDX_HYPERCALL_r11(%rdi)
- movq %r12, TDX_HYPERCALL_r12(%rdi)
- movq %r13, TDX_HYPERCALL_r13(%rdi)
- movq %r14, TDX_HYPERCALL_r14(%rdi)
- movq %r15, TDX_HYPERCALL_r15(%rdi)
+ movq %r8, TDX_HYPERCALL_r8(%rax)
+ movq %r9, TDX_HYPERCALL_r9(%rax)
+ movq %r10, TDX_HYPERCALL_r10(%rax)
+ movq %r11, TDX_HYPERCALL_r11(%rax)
+ movq %r12, TDX_HYPERCALL_r12(%rax)
+ movq %r13, TDX_HYPERCALL_r13(%rax)
+ movq %r14, TDX_HYPERCALL_r14(%rax)
+ movq %r15, TDX_HYPERCALL_r15(%rax)
+ movq %rdi, TDX_HYPERCALL_rdi(%rax)
+ movq %rsi, TDX_HYPERCALL_rsi(%rax)
+ movq %rbx, TDX_HYPERCALL_rbx(%rax)
+ movq %rdx, TDX_HYPERCALL_rdx(%rax)
.Lout:
+ /* TDVMCALL leaf return code is in R10 */
+ movq %r10, %rax
+
/*
* 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 R12-R15). R12-R15
- * context will be restored.
+ * 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 %rbp
+ pop %rbx
pop %r12
pop %r13
pop %r14
diff --git a/arch/x86/include/asm/shared/tdx.h b/arch/x86/include/asm/shared/tdx.h
index e53f26228fbb..8068faa52de1 100644
--- a/arch/x86/include/asm/shared/tdx.h
+++ b/arch/x86/include/asm/shared/tdx.h
@@ -22,12 +22,18 @@
* This is a software only structure and not part of the TDX module/VMM ABI.
*/
struct tdx_hypercall_args {
+ u64 r8;
+ u64 r9;
u64 r10;
u64 r11;
u64 r12;
u64 r13;
u64 r14;
u64 r15;
+ u64 rdi;
+ u64 rsi;
+ u64 rbx;
+ u64 rdx;
};

/* Used to request services from the VMM */
diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
index 437308004ef2..9f09947495e2 100644
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -75,12 +75,18 @@ static void __used common(void)
OFFSET(TDX_MODULE_r11, tdx_module_output, r11);

BLANK();
+ OFFSET(TDX_HYPERCALL_r8, tdx_hypercall_args, r8);
+ OFFSET(TDX_HYPERCALL_r9, tdx_hypercall_args, r9);
OFFSET(TDX_HYPERCALL_r10, tdx_hypercall_args, r10);
OFFSET(TDX_HYPERCALL_r11, tdx_hypercall_args, r11);
OFFSET(TDX_HYPERCALL_r12, tdx_hypercall_args, r12);
OFFSET(TDX_HYPERCALL_r13, tdx_hypercall_args, r13);
OFFSET(TDX_HYPERCALL_r14, tdx_hypercall_args, r14);
OFFSET(TDX_HYPERCALL_r15, tdx_hypercall_args, r15);
+ OFFSET(TDX_HYPERCALL_rdi, tdx_hypercall_args, rdi);
+ OFFSET(TDX_HYPERCALL_rsi, tdx_hypercall_args, rsi);
+ OFFSET(TDX_HYPERCALL_rbx, tdx_hypercall_args, rbx);
+ OFFSET(TDX_HYPERCALL_rdx, tdx_hypercall_args, rdx);

BLANK();
OFFSET(BP_scratch, boot_params, scratch);
--
2.25.1