[PATCH 00/11] x86/entry: Clean up entry code

[PATCH 00/11] x86/entry: Clean up entry code

[Lai Jiangshan]

From: Lai Jiangshan <laijs@linux.alibaba.com>

This patchset moves the stack-switch code to the place where
error_entry() return, distangles error_entry() from XENpv and makes
entry_INT80_compat use idtentry macro.

This patchset is highly related to XENpv, because it does the extra
cleanup to convert SWAPGS to swapgs after major cleanup is done.

After error_entry() is distangled from XENpv, a branch in sync_regs()
is removed to.

Patch 1-10 are picked from the patchset
https://lore.kernel.org/lkml/20211126101209.8613-1-jiangshanlai@gmail.com/
which coverts ASM code to C code.  These patches are prepared for that
purpose.  But this patchset has it own value: it simplifies the stack
switch, avoids leaving the old stack inside a function, and separates
XENpv code with native code without adding new code which can lead to
more cleanups.

Patch 11 is new in this patchset.

Lai Jiangshan (11):
  x86/entry: Use swapgs and native_iret directly in
    swapgs_restore_regs_and_return_to_usermode
  x86/traps: Move pt_regs only in fixup_bad_iret()
  x86/entry: Switch the stack after error_entry() returns
  x86/entry: move PUSH_AND_CLEAR_REGS out of error_entry
  x86/entry: Move cld to the start of idtentry
  x86/entry: Don't call error_entry for XENPV
  x86/entry: Convert SWAPGS to swapgs in error_entry()
  x86/entry: Use idtentry macro for entry_INT80_compat
  x86/entry: Convert SWAPGS to swapgs in entry_SYSENTER_compat()
  x86: Remove the definition of SWAPGS
  x86/entry: Remove the branch in sync_regs()

 arch/x86/entry/entry_64.S        |  65 +++++++++++++------
 arch/x86/entry/entry_64_compat.S | 104 +------------------------------
 arch/x86/include/asm/idtentry.h  |  47 ++++++++++++++
 arch/x86/include/asm/irqflags.h  |   2 -
 arch/x86/include/asm/proto.h     |   4 --
 arch/x86/include/asm/traps.h     |   2 +-
 arch/x86/kernel/traps.c          |  25 ++++----
 7 files changed, 107 insertions(+), 142 deletions(-)

-- 
2.19.1.6.gb485710b

[PATCH 01/11] x86/entry: Use swapgs and native_iret directly in swapgs_restore_regs_and_return_to_usermode

[Lai Jiangshan]

From: Lai Jiangshan <laijs@linux.alibaba.com>

swapgs_restore_regs_and_return_to_usermode() is used in native code
(non-xenpv) only now, so it doesn't need the PV-aware SWAPGS and
INTERRUPT_RETURN.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
 arch/x86/entry/entry_64.S | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 97b1f84bb53f..d95a02ecee16 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -608,8 +608,8 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL)
 
 	/* Restore RDI. */
 	popq	%rdi
-	SWAPGS
-	INTERRUPT_RETURN
+	swapgs
+	jmp	native_iret
 
 
 SYM_INNER_LABEL(restore_regs_and_return_to_kernel, SYM_L_GLOBAL)
-- 
2.19.1.6.gb485710b

[PATCH 02/11] x86/traps: Move pt_regs only in fixup_bad_iret()

[Lai Jiangshan]

From: Lai Jiangshan <laijs@linux.alibaba.com>

fixup_bad_iret() and sync_regs() have similar arguments and do similar
work that copies full or partial pt_regs to a place and switches stack
after return.  They are quite the same, but fixup_bad_iret() not only
copies the pt_regs but also the return address of error_entry() while
sync_regs() copies the pt_regs only and the return address of
error_entry() was preserved and handled in ASM code.

This patch makes fixup_bad_iret() work like sync_regs() and the
handling of the return address of error_entry() is moved in ASM code.

It removes the need to use the struct bad_iret_stack, simplifies
fixup_bad_iret() and makes the ASM error_entry() call fixup_bad_iret()
as the same as calling sync_regs() which adds readability because
the calling patterns are exactly the same.

It is prepared for later patch to do the stack switch after the
error_entry() which simplifies the code further.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
 arch/x86/entry/entry_64.S    |  5 ++++-
 arch/x86/include/asm/traps.h |  2 +-
 arch/x86/kernel/traps.c      | 17 ++++++-----------
 3 files changed, 11 insertions(+), 13 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index d95a02ecee16..f8faff3ca61e 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1040,9 +1040,12 @@ SYM_CODE_START_LOCAL(error_entry)
 	 * Pretend that the exception came from user mode: set up pt_regs
 	 * as if we faulted immediately after IRET.
 	 */
-	mov	%rsp, %rdi
+	popq	%r12				/* save return addr in %12 */
+	movq	%rsp, %rdi			/* arg0 = pt_regs pointer */
 	call	fixup_bad_iret
 	mov	%rax, %rsp
+	ENCODE_FRAME_POINTER
+	pushq	%r12
 	jmp	.Lerror_entry_from_usermode_after_swapgs
 SYM_CODE_END(error_entry)
 
diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h
index 6221be7cafc3..1cdd7e8bcba7 100644
--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -13,7 +13,7 @@
 #ifdef CONFIG_X86_64
 asmlinkage __visible notrace struct pt_regs *sync_regs(struct pt_regs *eregs);
 asmlinkage __visible notrace
-struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s);
+struct pt_regs *fixup_bad_iret(struct pt_regs *bad_regs);
 void __init trap_init(void);
 asmlinkage __visible noinstr struct pt_regs *vc_switch_off_ist(struct pt_regs *eregs);
 #endif
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index c9d566dcf89a..a6c0bc9ee36f 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -761,13 +761,8 @@ asmlinkage __visible noinstr struct pt_regs *vc_switch_off_ist(struct pt_regs *r
 }
 #endif
 
-struct bad_iret_stack {
-	void *error_entry_ret;
-	struct pt_regs regs;
-};
-
 asmlinkage __visible noinstr
-struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
+struct pt_regs *fixup_bad_iret(struct pt_regs *bad_regs)
 {
 	/*
 	 * This is called from entry_64.S early in handling a fault
@@ -777,19 +772,19 @@ struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
 	 * just below the IRET frame) and we want to pretend that the
 	 * exception came from the IRET target.
 	 */
-	struct bad_iret_stack tmp, *new_stack =
-		(struct bad_iret_stack *)__this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
+	struct pt_regs tmp, *new_stack =
+		(struct pt_regs *)__this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
 
 	/* Copy the IRET target to the temporary storage. */
-	__memcpy(&tmp.regs.ip, (void *)s->regs.sp, 5*8);
+	__memcpy(&tmp.ip, (void *)bad_regs->sp, 5*8);
 
 	/* Copy the remainder of the stack from the current stack. */
-	__memcpy(&tmp, s, offsetof(struct bad_iret_stack, regs.ip));
+	__memcpy(&tmp, bad_regs, offsetof(struct pt_regs, ip));
 
 	/* Update the entry stack */
 	__memcpy(new_stack, &tmp, sizeof(tmp));
 
-	BUG_ON(!user_mode(&new_stack->regs));
+	BUG_ON(!user_mode(new_stack));
 	return new_stack;
 }
 #endif
-- 
2.19.1.6.gb485710b

[PATCH 03/11] x86/entry: Switch the stack after error_entry() returns

[Lai Jiangshan]

From: Lai Jiangshan <laijs@linux.alibaba.com>

error_entry() calls sync_regs() to settle/copy the pt_regs and switches
the stack directly after sync_regs().  But error_entry() itself is also
a function call, the switching has to handle the return address of it
together, which causes the work complicated and tangly.

Switching to the stack after error_entry() makes the code simpler and
intuitive.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
 arch/x86/entry/entry_64.S | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index f8faff3ca61e..6baa7413f7eb 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -323,6 +323,8 @@ SYM_CODE_END(ret_from_fork)
 .macro idtentry_body cfunc has_error_code:req
 
 	call	error_entry
+	movq	%rax, %rsp			/* switch stack settled by sync_regs() */
+	ENCODE_FRAME_POINTER
 	UNWIND_HINT_REGS
 
 	movq	%rsp, %rdi			/* pt_regs pointer into 1st argument*/
@@ -981,14 +983,10 @@ SYM_CODE_START_LOCAL(error_entry)
 	/* We have user CR3.  Change to kernel CR3. */
 	SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
 
+	leaq	8(%rsp), %rdi			/* arg0 = pt_regs pointer */
 .Lerror_entry_from_usermode_after_swapgs:
 	/* Put us onto the real thread stack. */
-	popq	%r12				/* save return addr in %12 */
-	movq	%rsp, %rdi			/* arg0 = pt_regs pointer */
 	call	sync_regs
-	movq	%rax, %rsp			/* switch stack */
-	ENCODE_FRAME_POINTER
-	pushq	%r12
 	ret
 
 	/*
@@ -1020,6 +1018,7 @@ SYM_CODE_START_LOCAL(error_entry)
 	 */
 .Lerror_entry_done_lfence:
 	FENCE_SWAPGS_KERNEL_ENTRY
+	leaq	8(%rsp), %rax			/* return pt_regs pointer */
 	ret
 
 .Lbstep_iret:
@@ -1040,12 +1039,9 @@ SYM_CODE_START_LOCAL(error_entry)
 	 * Pretend that the exception came from user mode: set up pt_regs
 	 * as if we faulted immediately after IRET.
 	 */
-	popq	%r12				/* save return addr in %12 */
-	movq	%rsp, %rdi			/* arg0 = pt_regs pointer */
+	leaq	8(%rsp), %rdi			/* arg0 = pt_regs pointer */
 	call	fixup_bad_iret
-	mov	%rax, %rsp
-	ENCODE_FRAME_POINTER
-	pushq	%r12
+	mov	%rax, %rdi
 	jmp	.Lerror_entry_from_usermode_after_swapgs
 SYM_CODE_END(error_entry)
 
-- 
2.19.1.6.gb485710b

[PATCH 04/11] x86/entry: move PUSH_AND_CLEAR_REGS out of error_entry

[Lai Jiangshan]

From: Lai Jiangshan <laijs@linux.alibaba.com>

Moving PUSH_AND_CLEAR_REGS out of error_entry doesn't change any
functionality.  It will enlarge the size:

size arch/x86/entry/entry_64.o.before:
   text	   data	    bss	    dec	    hex	filename
  17916	    384	      0	  18300	   477c	arch/x86/entry/entry_64.o

size --format=SysV arch/x86/entry/entry_64.o.before:
.entry.text                      5528      0
.orc_unwind                      6456      0
.orc_unwind_ip                   4304      0

size arch/x86/entry/entry_64.o.after:
   text	   data	    bss	    dec	    hex	filename
  26868	    384	      0	  27252	   6a74	arch/x86/entry/entry_64.o

size --format=SysV arch/x86/entry/entry_64.o.after:
.entry.text                      8200      0
.orc_unwind                     10224      0
.orc_unwind_ip                   6816      0

But .entry.text in x86_64 is 2M aligned, enlarging it to 8.2k doesn't
enlarge the final text size.

The tables .orc_unwind[_ip] are enlarged due to it adds many pushes.

It is prepared for not calling error_entry() from XENPV in later patch
and for future converting the whole error_entry into C code.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
 arch/x86/entry/entry_64.S | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 6baa7413f7eb..72ceb4b70822 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -322,6 +322,9 @@ SYM_CODE_END(ret_from_fork)
  */
 .macro idtentry_body cfunc has_error_code:req
 
+	PUSH_AND_CLEAR_REGS
+	ENCODE_FRAME_POINTER
+
 	call	error_entry
 	movq	%rax, %rsp			/* switch stack settled by sync_regs() */
 	ENCODE_FRAME_POINTER
@@ -969,8 +972,6 @@ SYM_CODE_END(paranoid_exit)
 SYM_CODE_START_LOCAL(error_entry)
 	UNWIND_HINT_FUNC
 	cld
-	PUSH_AND_CLEAR_REGS save_ret=1
-	ENCODE_FRAME_POINTER 8
 	testb	$3, CS+8(%rsp)
 	jz	.Lerror_kernelspace
 
-- 
2.19.1.6.gb485710b

[PATCH 05/11] x86/entry: Move cld to the start of idtentry

[Lai Jiangshan]

From: Lai Jiangshan <laijs@linux.alibaba.com>

Make it next to CLAC

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
 arch/x86/entry/entry_64.S | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 72ceb4b70822..ee1d4adcdab0 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -356,6 +356,7 @@ SYM_CODE_END(ret_from_fork)
 SYM_CODE_START(\asmsym)
 	UNWIND_HINT_IRET_REGS offset=\has_error_code*8
 	ASM_CLAC
+	cld
 
 	.if \has_error_code == 0
 		pushq	$-1			/* ORIG_RAX: no syscall to restart */
@@ -423,6 +424,7 @@ SYM_CODE_END(\asmsym)
 SYM_CODE_START(\asmsym)
 	UNWIND_HINT_IRET_REGS
 	ASM_CLAC
+	cld
 
 	pushq	$-1			/* ORIG_RAX: no syscall to restart */
 
@@ -478,6 +480,7 @@ SYM_CODE_END(\asmsym)
 SYM_CODE_START(\asmsym)
 	UNWIND_HINT_IRET_REGS
 	ASM_CLAC
+	cld
 
 	/*
 	 * If the entry is from userspace, switch stacks and treat it as
@@ -539,6 +542,7 @@ SYM_CODE_END(\asmsym)
 SYM_CODE_START(\asmsym)
 	UNWIND_HINT_IRET_REGS offset=8
 	ASM_CLAC
+	cld
 
 	/* paranoid_entry returns GS information for paranoid_exit in EBX. */
 	call	paranoid_entry
@@ -853,7 +857,6 @@ SYM_CODE_END(xen_failsafe_callback)
  */
 SYM_CODE_START_LOCAL(paranoid_entry)
 	UNWIND_HINT_FUNC
-	cld
 	PUSH_AND_CLEAR_REGS save_ret=1
 	ENCODE_FRAME_POINTER 8
 
@@ -971,7 +974,6 @@ SYM_CODE_END(paranoid_exit)
  */
 SYM_CODE_START_LOCAL(error_entry)
 	UNWIND_HINT_FUNC
-	cld
 	testb	$3, CS+8(%rsp)
 	jz	.Lerror_kernelspace
 
@@ -1104,6 +1106,7 @@ SYM_CODE_START(asm_exc_nmi)
 	 */
 
 	ASM_CLAC
+	cld
 
 	/* Use %rdx as our temp variable throughout */
 	pushq	%rdx
@@ -1123,7 +1126,6 @@ SYM_CODE_START(asm_exc_nmi)
 	 */
 
 	swapgs
-	cld
 	FENCE_SWAPGS_USER_ENTRY
 	SWITCH_TO_KERNEL_CR3 scratch_reg=%rdx
 	movq	%rsp, %rdx
-- 
2.19.1.6.gb485710b

[PATCH 06/11] x86/entry: Don't call error_entry for XENPV

[Lai Jiangshan]

From: Lai Jiangshan <laijs@linux.alibaba.com>

When in XENPV, it is already in the task stack, and it can't fault
for native_iret() nor native_load_gs_index() since XENPV uses its own
pvops for iret and load_gs_index().  And it doesn't need to switch CR3.
So there is no reason to call error_entry() in XENPV.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
 arch/x86/entry/entry_64.S | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index ee1d4adcdab0..383070aa9272 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -325,8 +325,17 @@ SYM_CODE_END(ret_from_fork)
 	PUSH_AND_CLEAR_REGS
 	ENCODE_FRAME_POINTER
 
-	call	error_entry
-	movq	%rax, %rsp			/* switch stack settled by sync_regs() */
+	/*
+	 * Call error_entry and switch stack settled by sync_regs().
+	 *
+	 * When in XENPV, it is already in the task stack, and it can't fault
+	 * for native_iret() nor native_load_gs_index() since XENPV uses its
+	 * own pvops for iret and load_gs_index().  And it doesn't need to
+	 * switch CR3.  So it can skip invoking error_entry().
+	 */
+	ALTERNATIVE "call error_entry; movq %rax, %rsp", \
+		"", X86_FEATURE_XENPV
+
 	ENCODE_FRAME_POINTER
 	UNWIND_HINT_REGS
 
-- 
2.19.1.6.gb485710b

[PATCH 07/11] x86/entry: Convert SWAPGS to swapgs in error_entry()

[Lai Jiangshan]

From: Lai Jiangshan <laijs@linux.alibaba.com>

XENPV doesn't use error_entry() anymore, so the pv-aware SWAPGS can be
changed to native swapgs.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
 arch/x86/entry/entry_64.S | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 383070aa9272..6100007fd03f 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -990,7 +990,7 @@ SYM_CODE_START_LOCAL(error_entry)
 	 * We entered from user mode or we're pretending to have entered
 	 * from user mode due to an IRET fault.
 	 */
-	SWAPGS
+	swapgs
 	FENCE_SWAPGS_USER_ENTRY
 	/* We have user CR3.  Change to kernel CR3. */
 	SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
@@ -1022,7 +1022,7 @@ SYM_CODE_START_LOCAL(error_entry)
 	 * gsbase and proceed.  We'll fix up the exception and land in
 	 * .Lgs_change's error handler with kernel gsbase.
 	 */
-	SWAPGS
+	swapgs
 
 	/*
 	 * Issue an LFENCE to prevent GS speculation, regardless of whether it is a
@@ -1043,7 +1043,7 @@ SYM_CODE_START_LOCAL(error_entry)
 	 * We came from an IRET to user mode, so we have user
 	 * gsbase and CR3.  Switch to kernel gsbase and CR3:
 	 */
-	SWAPGS
+	swapgs
 	FENCE_SWAPGS_USER_ENTRY
 	SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
 
-- 
2.19.1.6.gb485710b

[PATCH 08/11] x86/entry: Use idtentry macro for entry_INT80_compat

[Lai Jiangshan]

From: Lai Jiangshan <laijs@linux.alibaba.com>

entry_INT80_compat is identical to idtentry macro except a special
handling for %rax in the prolog.

Add the prolog to idtentry and use idtentry for entry_INT80_compat.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
 arch/x86/entry/entry_64.S        |  18 ++++++
 arch/x86/entry/entry_64_compat.S | 102 -------------------------------
 arch/x86/include/asm/idtentry.h  |  47 ++++++++++++++
 arch/x86/include/asm/proto.h     |   4 --
 4 files changed, 65 insertions(+), 106 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 6100007fd03f..1fd5efaa99b3 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -371,6 +371,24 @@ SYM_CODE_START(\asmsym)
 		pushq	$-1			/* ORIG_RAX: no syscall to restart */
 	.endif
 
+	.if \vector == IA32_SYSCALL_VECTOR
+		/*
+		 * User tracing code (ptrace or signal handlers) might assume
+		 * that the saved RAX contains a 32-bit number when we're
+		 * invoking a 32-bit syscall.  Just in case the high bits are
+		 * nonzero, zero-extend the syscall number.  (This could almost
+		 * certainly be deleted with no ill effects.)
+		 */
+		movl	%eax, %eax
+
+		/*
+		 * do_int80_syscall_32() expects regs->orig_ax to be user ax,
+		 * and regs->ax to be $-ENOSYS.
+		 */
+		movq	%rax, (%rsp)
+		movq	$-ENOSYS, %rax
+	.endif
+
 	.if \vector == X86_TRAP_BP
 		/*
 		 * If coming from kernel space, create a 6-word gap to allow the
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 0051cf5c792d..a4fcea0cab14 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -311,105 +311,3 @@ sysret32_from_system_call:
 	swapgs
 	sysretl
 SYM_CODE_END(entry_SYSCALL_compat)
-
-/*
- * 32-bit legacy system call entry.
- *
- * 32-bit x86 Linux system calls traditionally used the INT $0x80
- * instruction.  INT $0x80 lands here.
- *
- * This entry point can be used by 32-bit and 64-bit programs to perform
- * 32-bit system calls.  Instances of INT $0x80 can be found inline in
- * various programs and libraries.  It is also used by the vDSO's
- * __kernel_vsyscall fallback for hardware that doesn't support a faster
- * entry method.  Restarted 32-bit system calls also fall back to INT
- * $0x80 regardless of what instruction was originally used to do the
- * system call.
- *
- * This is considered a slow path.  It is not used by most libc
- * implementations on modern hardware except during process startup.
- *
- * Arguments:
- * eax  system call number
- * ebx  arg1
- * ecx  arg2
- * edx  arg3
- * esi  arg4
- * edi  arg5
- * ebp  arg6
- */
-SYM_CODE_START(entry_INT80_compat)
-	UNWIND_HINT_EMPTY
-	/*
-	 * Interrupts are off on entry.
-	 */
-	ASM_CLAC			/* Do this early to minimize exposure */
-	SWAPGS
-
-	/*
-	 * User tracing code (ptrace or signal handlers) might assume that
-	 * the saved RAX contains a 32-bit number when we're invoking a 32-bit
-	 * syscall.  Just in case the high bits are nonzero, zero-extend
-	 * the syscall number.  (This could almost certainly be deleted
-	 * with no ill effects.)
-	 */
-	movl	%eax, %eax
-
-	/* switch to thread stack expects orig_ax and rdi to be pushed */
-	pushq	%rax			/* pt_regs->orig_ax */
-	pushq	%rdi			/* pt_regs->di */
-
-	/* Need to switch before accessing the thread stack. */
-	SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi
-
-	/* In the Xen PV case we already run on the thread stack. */
-	ALTERNATIVE "", "jmp .Lint80_keep_stack", X86_FEATURE_XENPV
-
-	movq	%rsp, %rdi
-	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp
-
-	pushq	6*8(%rdi)		/* regs->ss */
-	pushq	5*8(%rdi)		/* regs->rsp */
-	pushq	4*8(%rdi)		/* regs->eflags */
-	pushq	3*8(%rdi)		/* regs->cs */
-	pushq	2*8(%rdi)		/* regs->ip */
-	pushq	1*8(%rdi)		/* regs->orig_ax */
-	pushq	(%rdi)			/* pt_regs->di */
-.Lint80_keep_stack:
-
-	pushq	%rsi			/* pt_regs->si */
-	xorl	%esi, %esi		/* nospec   si */
-	pushq	%rdx			/* pt_regs->dx */
-	xorl	%edx, %edx		/* nospec   dx */
-	pushq	%rcx			/* pt_regs->cx */
-	xorl	%ecx, %ecx		/* nospec   cx */
-	pushq	$-ENOSYS		/* pt_regs->ax */
-	pushq   %r8			/* pt_regs->r8 */
-	xorl	%r8d, %r8d		/* nospec   r8 */
-	pushq   %r9			/* pt_regs->r9 */
-	xorl	%r9d, %r9d		/* nospec   r9 */
-	pushq   %r10			/* pt_regs->r10*/
-	xorl	%r10d, %r10d		/* nospec   r10 */
-	pushq   %r11			/* pt_regs->r11 */
-	xorl	%r11d, %r11d		/* nospec   r11 */
-	pushq   %rbx                    /* pt_regs->rbx */
-	xorl	%ebx, %ebx		/* nospec   rbx */
-	pushq   %rbp                    /* pt_regs->rbp */
-	xorl	%ebp, %ebp		/* nospec   rbp */
-	pushq   %r12                    /* pt_regs->r12 */
-	xorl	%r12d, %r12d		/* nospec   r12 */
-	pushq   %r13                    /* pt_regs->r13 */
-	xorl	%r13d, %r13d		/* nospec   r13 */
-	pushq   %r14                    /* pt_regs->r14 */
-	xorl	%r14d, %r14d		/* nospec   r14 */
-	pushq   %r15                    /* pt_regs->r15 */
-	xorl	%r15d, %r15d		/* nospec   r15 */
-
-	UNWIND_HINT_REGS
-
-	cld
-
-	movq	%rsp, %rdi
-	call	do_int80_syscall_32
-	jmp	swapgs_restore_regs_and_return_to_usermode
-SYM_CODE_END(entry_INT80_compat)
diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index 1345088e9902..38cb2e0dc2c7 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -204,6 +204,20 @@ __visible noinstr void func(struct pt_regs *regs,			\
 									\
 static noinline void __##func(struct pt_regs *regs, u32 vector)
 
+/**
+ * DECLARE_IDTENTRY_IA32_EMULATION - Declare functions for int80
+ * @vector:	Vector number (ignored for C)
+ * @asm_func:	Function name of the entry point
+ * @cfunc:	The C handler called from the ASM entry point (ignored for C)
+ *
+ * Declares two functions:
+ * - The ASM entry point: asm_func
+ * - The XEN PV trap entry point: xen_##asm_func (maybe unused)
+ */
+#define DECLARE_IDTENTRY_IA32_EMULATION(vector, asm_func, cfunc)	\
+	asmlinkage void asm_func(void);					\
+	asmlinkage void xen_##asm_func(void)
+
 /**
  * DECLARE_IDTENTRY_SYSVEC - Declare functions for system vector entry points
  * @vector:	Vector number (ignored for C)
@@ -430,6 +444,35 @@ __visible noinstr void func(struct pt_regs *regs,			\
 #define DECLARE_IDTENTRY_ERRORCODE(vector, func)			\
 	idtentry vector asm_##func func has_error_code=1
 
+/*
+ * 32-bit legacy system call entry.
+ *
+ * 32-bit x86 Linux system calls traditionally used the INT $0x80
+ * instruction.  INT $0x80 lands here.
+ *
+ * This entry point can be used by 32-bit and 64-bit programs to perform
+ * 32-bit system calls.  Instances of INT $0x80 can be found inline in
+ * various programs and libraries.  It is also used by the vDSO's
+ * __kernel_vsyscall fallback for hardware that doesn't support a faster
+ * entry method.  Restarted 32-bit system calls also fall back to INT
+ * $0x80 regardless of what instruction was originally used to do the
+ * system call.
+ *
+ * This is considered a slow path.  It is not used by most libc
+ * implementations on modern hardware except during process startup.
+ *
+ * Arguments:
+ * eax  system call number
+ * ebx  arg1
+ * ecx  arg2
+ * edx  arg3
+ * esi  arg4
+ * edi  arg5
+ * ebp  arg6
+ */
+#define DECLARE_IDTENTRY_IA32_EMULATION(vector, asm_func, cfunc)	\
+	idtentry vector asm_func cfunc has_error_code=0
+
 /* Special case for 32bit IRET 'trap'. Do not emit ASM code */
 #define DECLARE_IDTENTRY_SW(vector, func)
 
@@ -631,6 +674,10 @@ DECLARE_IDTENTRY_IRQ(X86_TRAP_OTHER,	common_interrupt);
 DECLARE_IDTENTRY_IRQ(X86_TRAP_OTHER,	spurious_interrupt);
 #endif
 
+#ifdef CONFIG_IA32_EMULATION
+DECLARE_IDTENTRY_IA32_EMULATION(IA32_SYSCALL_VECTOR,	entry_INT80_compat, do_int80_syscall_32);
+#endif
+
 /* System vector entry points */
 #ifdef CONFIG_X86_LOCAL_APIC
 DECLARE_IDTENTRY_SYSVEC(ERROR_APIC_VECTOR,		sysvec_error_interrupt);
diff --git a/arch/x86/include/asm/proto.h b/arch/x86/include/asm/proto.h
index feed36d44d04..c4d331fe65ff 100644
--- a/arch/x86/include/asm/proto.h
+++ b/arch/x86/include/asm/proto.h
@@ -28,10 +28,6 @@ void entry_SYSENTER_compat(void);
 void __end_entry_SYSENTER_compat(void);
 void entry_SYSCALL_compat(void);
 void entry_SYSCALL_compat_safe_stack(void);
-void entry_INT80_compat(void);
-#ifdef CONFIG_XEN_PV
-void xen_entry_INT80_compat(void);
-#endif
 #endif
 
 void x86_configure_nx(void);
-- 
2.19.1.6.gb485710b

[PATCH 09/11] x86/entry: Convert SWAPGS to swapgs in entry_SYSENTER_compat()

[Lai Jiangshan]

From: Lai Jiangshan <laijs@linux.alibaba.com>

XENPV has its own entry point for SYSENTER, it doesn't use
entry_SYSENTER_compat.  So the pv-awared SWAPGS can be changed to
swapgs.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
 arch/x86/entry/entry_64_compat.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index a4fcea0cab14..72e017c3941f 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -49,7 +49,7 @@
 SYM_CODE_START(entry_SYSENTER_compat)
 	UNWIND_HINT_EMPTY
 	/* Interrupts are off on entry. */
-	SWAPGS
+	swapgs
 
 	pushq	%rax
 	SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
-- 
2.19.1.6.gb485710b

[PATCH 10/11] x86: Remove the definition of SWAPGS

[Lai Jiangshan]

From: Lai Jiangshan <laijs@linux.alibaba.com>

There is no user of the pv-aware SWAPGS anymore.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
 arch/x86/include/asm/irqflags.h | 2 --
 1 file changed, 2 deletions(-)

diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h
index 87761396e8cc..ac2e4cc47210 100644
--- a/arch/x86/include/asm/irqflags.h
+++ b/arch/x86/include/asm/irqflags.h
@@ -140,13 +140,11 @@ static __always_inline void arch_local_irq_restore(unsigned long flags)
 #else
 #ifdef CONFIG_X86_64
 #ifdef CONFIG_XEN_PV
-#define SWAPGS	ALTERNATIVE "swapgs", "", X86_FEATURE_XENPV
 #define INTERRUPT_RETURN						\
 	ANNOTATE_RETPOLINE_SAFE;					\
 	ALTERNATIVE_TERNARY("jmp *paravirt_iret(%rip);",		\
 		X86_FEATURE_XENPV, "jmp xen_iret;", "jmp native_iret;")
 #else
-#define SWAPGS	swapgs
 #define INTERRUPT_RETURN	jmp native_iret
 #endif
 #endif
-- 
2.19.1.6.gb485710b

[PATCH 11/11] x86/entry: Remove the branch in sync_regs()

[Lai Jiangshan]

From: Lai Jiangshan <laijs@linux.alibaba.com>

In non-xenpv, the sp0 is the trampoline stack, and sync_regs() is
called on non-xenpv only since error_entry is not called on xenpv, so
the stack must be the trampoline stack or one of the IST stack and the
check in sync_regs() is unneeded.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
 arch/x86/kernel/traps.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index a6c0bc9ee36f..63cdb7aedd67 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -708,13 +708,15 @@ DEFINE_IDTENTRY_RAW(exc_int3)
 /*
  * Help handler running on a per-cpu (IST or entry trampoline) stack
  * to switch to the normal thread stack if the interrupted code was in
- * user mode. The actual stack switch is done in entry_64.S
+ * user mode.  The actual stack switch is done in entry_64.S.  It is not
+ * called from XENPV and the caller has ensured it is not on the thread
+ * stack.
  */
 asmlinkage __visible noinstr struct pt_regs *sync_regs(struct pt_regs *eregs)
 {
 	struct pt_regs *regs = (struct pt_regs *)this_cpu_read(cpu_current_top_of_stack) - 1;
-	if (regs != eregs)
-		*regs = *eregs;
+
+	*regs = *eregs;
 	return regs;
 }
 
-- 
2.19.1.6.gb485710b

Re: [PATCH 01/11] x86/entry: Use swapgs and native_iret directly in swapgs_restore_regs_and_return_to_usermode

[Juergen Gross]

[-- Attachment #1.1.1: Type: text/plain, Size: 377 bytes --]

On 08.12.21 12:08, Lai Jiangshan wrote:
> From: Lai Jiangshan <laijs@linux.alibaba.com>
> 
> swapgs_restore_regs_and_return_to_usermode() is used in native code
> (non-xenpv) only now, so it doesn't need the PV-aware SWAPGS and
> INTERRUPT_RETURN.
> 
> Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>

Reviewed-by: Juergen Gross <jgross@suse.com>


Juergen

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