2019-10-23 17:08:53

by Thomas Gleixner

Subject: [patch V2 06/17] x86/entry/32: Remove redundant interrupt disable

Now that the trap handlers return with interrupts disabled, the
unconditional disabling of interrupts in the low level entry code can be
removed along with the trace calls and the misnomed preempt_stop macro.
As a consequence ret_from_exception and ret_from_intr collapse.

Add a debug check to verify that interrupts are disabled depending on
CONFIG_DEBUG_ENTRY.

Signed-off-by: Thomas Gleixner <[email protected]>
---
arch/x86/entry/entry_32.S | 21 ++++++---------------
1 file changed, 6 insertions(+), 15 deletions(-)

--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -63,12 +63,6 @@
* enough to patch inline, increasing performance.
*/

-#ifdef CONFIG_PREEMPTION
-# define preempt_stop(clobbers) DISABLE_INTERRUPTS(clobbers); TRACE_IRQS_OFF
-#else
-# define preempt_stop(clobbers)
-#endif
-
.macro TRACE_IRQS_IRET
#ifdef CONFIG_TRACE_IRQFLAGS
testl $X86_EFLAGS_IF, PT_EFLAGS(%esp) # interrupts off?
@@ -809,8 +803,7 @@ END(ret_from_fork)
# userspace resumption stub bypassing syscall exit tracing
ALIGN
ret_from_exception:
- preempt_stop(CLBR_ANY)
-ret_from_intr:
+ DEBUG_ENTRY_ASSERT_IRQS_OFF
#ifdef CONFIG_VM86
movl PT_EFLAGS(%esp), %eax # mix EFLAGS and CS
movb PT_CS(%esp), %al
@@ -825,8 +818,6 @@ END(ret_from_fork)
cmpl $USER_RPL, %eax
jb restore_all_kernel # not returning to v8086 or userspace

- DISABLE_INTERRUPTS(CLBR_ANY)
- TRACE_IRQS_OFF
movl %esp, %eax
call prepare_exit_to_usermode
jmp restore_all
@@ -1084,7 +1075,7 @@ ENTRY(entry_INT80_32)

restore_all_kernel:
#ifdef CONFIG_PREEMPTION
- DISABLE_INTERRUPTS(CLBR_ANY)
+ /* Interrupts are disabled and debug-checked */
cmpl $0, PER_CPU_VAR(__preempt_count)
jnz .Lno_preempt
testl $X86_EFLAGS_IF, PT_EFLAGS(%esp) # interrupts off (exception path) ?
@@ -1189,7 +1180,7 @@ END(spurious_entries_start)
TRACE_IRQS_OFF
movl %esp, %eax
call smp_spurious_interrupt
- jmp ret_from_intr
+ jmp ret_from_exception
ENDPROC(common_spurious)
#endif

@@ -1207,7 +1198,7 @@ ENDPROC(common_spurious)
TRACE_IRQS_OFF
movl %esp, %eax
call do_IRQ
- jmp ret_from_intr
+ jmp ret_from_exception
ENDPROC(common_interrupt)

#define BUILD_INTERRUPT3(name, nr, fn) \
@@ -1219,7 +1210,7 @@ ENTRY(name) \
TRACE_IRQS_OFF \
movl %esp, %eax; \
call fn; \
- jmp ret_from_intr; \
+ jmp ret_from_exception; \
ENDPROC(name)

#define BUILD_INTERRUPT(name, nr) \
@@ -1366,7 +1357,7 @@ ENTRY(xen_do_upcall)
#ifndef CONFIG_PREEMPTION
call xen_maybe_preempt_hcall
#endif
- jmp ret_from_intr
+ jmp ret_from_exception
ENDPROC(xen_hypervisor_callback)

/*

2019-10-23 23:19:43

by Sean Christopherson

Subject: Re: [patch V2 06/17] x86/entry/32: Remove redundant interrupt disable

On Wed, Oct 23, 2019 at 02:27:11PM +0200, Thomas Gleixner wrote:
> Now that the trap handlers return with interrupts disabled, the
> unconditional disabling of interrupts in the low level entry code can be
> removed along with the trace calls and the misnomed preempt_stop macro.
> As a consequence ret_from_exception and ret_from_intr collapse.
>
> Add a debug check to verify that interrupts are disabled depending on
> CONFIG_DEBUG_ENTRY.
>
> Signed-off-by: Thomas Gleixner <[email protected]>
> ---

One nit below.

Reviewed-by: Sean Christopherson <[email protected]>

> arch/x86/entry/entry_32.S | 21 ++++++---------------
> 1 file changed, 6 insertions(+), 15 deletions(-)
>
> --- a/arch/x86/entry/entry_32.S
> +++ b/arch/x86/entry/entry_32.S
> @@ -1207,7 +1198,7 @@ ENDPROC(common_spurious)
> TRACE_IRQS_OFF
> movl %esp, %eax
> call do_IRQ
> - jmp ret_from_intr
> + jmp ret_from_exception
> ENDPROC(common_interrupt)
>
> #define BUILD_INTERRUPT3(name, nr, fn) \
> @@ -1219,7 +1210,7 @@ ENTRY(name) \
> TRACE_IRQS_OFF \
> movl %esp, %eax; \
> call fn; \
> - jmp ret_from_intr; \
> + jmp ret_from_exception; \

This backslash is now unaligned.

> ENDPROC(name)
>
> #define BUILD_INTERRUPT(name, nr) \
> @@ -1366,7 +1357,7 @@ ENTRY(xen_do_upcall)
> #ifndef CONFIG_PREEMPTION
> call xen_maybe_preempt_hcall
> #endif
> - jmp ret_from_intr
> + jmp ret_from_exception
> ENDPROC(xen_hypervisor_callback)
>
> /*
>
>

2019-11-08 10:43:30

by Alexandre Chartre

Subject: Re: [patch V2 06/17] x86/entry/32: Remove redundant interrupt disable

On 10/23/19 2:27 PM, Thomas Gleixner wrote:
> Now that the trap handlers return with interrupts disabled, the
> unconditional disabling of interrupts in the low level entry code can be
> removed along with the trace calls and the misnomed preempt_stop macro.
> As a consequence ret_from_exception and ret_from_intr collapse.
>
> Add a debug check to verify that interrupts are disabled depending on
> CONFIG_DEBUG_ENTRY.
>
> Signed-off-by: Thomas Gleixner <[email protected]>
> ---
> arch/x86/entry/entry_32.S | 21 ++++++---------------
> 1 file changed, 6 insertions(+), 15 deletions(-)
>

Reviewed-by: Alexandre Chartre <[email protected]>

alex.