[PATCH 1/4] sched: dovetail: pass thread-info bits to arch_dovetail_switch_finish()

[PATCH 1/4] sched: dovetail: pass thread-info bits to arch_dovetail_switch_finish()

[Philippe Gerum]

From: Philippe Gerum <rpm@xenomai.org>

The out-of-band switch tail code may need the thread-info work bits to
reinstate the current context appropriately, pass them to
arch_dovetail_switch_finish().

Signed-off-by: Philippe Gerum <rpm@xenomai.org>
---
 kernel/sched/core.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a1159a263894..75b506bb60bb 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -10902,6 +10902,7 @@ int dovetail_leave_inband(void)
 {
 	struct task_struct *p = current;
 	struct irq_pipeline_data *pd;
+	unsigned int ti_work;
 	unsigned long flags;
 
 	preempt_disable();
@@ -10930,7 +10931,8 @@ int dovetail_leave_inband(void)
 	 * architecture-specific fixups (e.g. fpu context reload).
 	 */
 	if (likely(__schedule(SM_NONE))) {
-		arch_dovetail_switch_finish(false);
+		ti_work = READ_ONCE(current_thread_info()->flags);
+		arch_dovetail_switch_finish(false, ti_work);
 		return 0;
 	}
 
@@ -10987,6 +10989,7 @@ bool dovetail_context_switch(struct dovetail_altsched_context *out,
 	struct task_struct *next, *prev, *last;
 	struct mm_struct *prev_mm, *next_mm;
 	bool inband_tail = false;
+	unsigned long ti_work;
 
 	WARN_ON_ONCE(dovetail_debug() && on_pipeline_entry());
 
@@ -11108,7 +11111,8 @@ bool dovetail_context_switch(struct dovetail_altsched_context *out,
 		lockdep_write_irqs_state(lockdep_irqs);
 	}
 
-	arch_dovetail_switch_finish(leave_inband);
+	ti_work = READ_ONCE(current_thread_info()->flags);
+	arch_dovetail_switch_finish(leave_inband, ti_work);
 
 	/*
 	 * inband_tail is true whenever we are finalizing a transition
-- 
2.34.1

[PATCH 2/4] ARM: dovetail: fix up arch_dovetail_switch_finish() signature

[Philippe Gerum]

From: Philippe Gerum <rpm@xenomai.org>

Signed-off-by: Philippe Gerum <rpm@xenomai.org>
---
 arch/arm/include/asm/dovetail.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/dovetail.h b/arch/arm/include/asm/dovetail.h
index 8f3a09391d06..ff754ff4d2db 100644
--- a/arch/arm/include/asm/dovetail.h
+++ b/arch/arm/include/asm/dovetail.h
@@ -25,7 +25,8 @@ static inline void arch_dovetail_exec_prepare(void)
 static inline void arch_dovetail_switch_prepare(bool leave_inband)
 { }
 
-static inline void arch_dovetail_switch_finish(bool enter_inband)
+static inline void arch_dovetail_switch_finish(bool enter_inband,
+					       unsigned int ti_work)
 { }
 
 #endif
-- 
2.34.1

[PATCH 3/4] arm64: dovetail: fix up arch_dovetail_switch_finish() signature

[Philippe Gerum]

From: Philippe Gerum <rpm@xenomai.org>

Signed-off-by: Philippe Gerum <rpm@xenomai.org>
---
 arch/arm64/include/asm/dovetail.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/dovetail.h b/arch/arm64/include/asm/dovetail.h
index 668679399406..f1c6605972cf 100644
--- a/arch/arm64/include/asm/dovetail.h
+++ b/arch/arm64/include/asm/dovetail.h
@@ -27,7 +27,8 @@ static inline void arch_dovetail_exec_prepare(void)
 static inline void arch_dovetail_switch_prepare(bool leave_inband)
 { }
 
-static inline void arch_dovetail_switch_finish(bool enter_inband)
+static inline void arch_dovetail_switch_finish(bool enter_inband,
+					       unsigned int ti_work)
 {
 	fpsimd_restore_current_oob();
 }
-- 
2.34.1

[PATCH 4/4] x86: dovetail: reinstate I/O bitmap on out-of-band user entry

[Philippe Gerum]

From: Philippe Gerum <rpm@xenomai.org>

We have to fix up the TSS with the proper I/O bitmap settings in
arch_dovetail_switch_finish() when the current task is about to
re-enter user mode on the out-of-band stage, along with reloading the
fpu context if need be.

This fixes an application crash observed when a user code would rely
on iopl() to raise the current I/O permissions, which would then
relinquish the CPU to a task invalidating them, before the initial
task eventually resumes in user mode on the out-of-band stage
(typically seen during an in-band -> out-of-band stage switch).

See https://xenomai.org/pipermail/xenomai/2022-March/047451.html.

Reported-by: Richard Weinberger <richard.weinberger@gmail.com>
Signed-off-by: Philippe Gerum <rpm@xenomai.org>
---
 arch/x86/include/asm/dovetail.h | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/dovetail.h b/arch/x86/include/asm/dovetail.h
index 9cf811fe98ba..0e0f93cb53d0 100644
--- a/arch/x86/include/asm/dovetail.h
+++ b/arch/x86/include/asm/dovetail.h
@@ -9,6 +9,7 @@
 #if !defined(__ASSEMBLY__) && defined(CONFIG_DOVETAIL)
 
 #include <asm/fpu/api.h>
+#include <asm/io_bitmap.h>
 
 static inline void arch_dovetail_exec_prepare(void)
 {
@@ -23,13 +24,17 @@ void arch_dovetail_switch_prepare(bool leave_inband)
 }
 
 static inline
-void arch_dovetail_switch_finish(bool enter_inband)
+void arch_dovetail_switch_finish(bool enter_inband, unsigned int ti_work)
 {
-	if (enter_inband)
+	if (enter_inband) {
 		fpu__resume_inband();
-	else if (!(current->flags & PF_KTHREAD) &&
-		test_thread_flag(TIF_NEED_FPU_LOAD))
-		switch_fpu_return();
+	} else {
+		  if (unlikely(ti_work & _TIF_IO_BITMAP))
+			  tss_update_io_bitmap();
+		  if (unlikely(ti_work & _TIF_NEED_FPU_LOAD &&
+				  !(current->flags & PF_KTHREAD)))
+			  switch_fpu_return();
+	}
 }
 
 #endif
-- 
2.34.1

Re: [PATCH 1/4] sched: dovetail: pass thread-info bits to arch_dovetail_switch_finish()

[Richard Weinberger]

On Sat, Apr 2, 2022 at 4:23 PM Philippe Gerum via Xenomai
<xenomai@xenomai.org> wrote:

> -       arch_dovetail_switch_finish(leave_inband);
> +       ti_work = READ_ONCE(current_thread_info()->flags);
> +       arch_dovetail_switch_finish(leave_inband, ti_work);

Why are you passing ti_work as parameter? AFAIU you can
use current_thread_info()->flags directly in arch_dovetail_switch_finish().

-- 
Thanks,
//richard

Re: [PATCH 1/4] sched: dovetail: pass thread-info bits to arch_dovetail_switch_finish()

[Philippe Gerum]

Richard Weinberger <richard.weinberger@gmail.com> writes:

> On Sat, Apr 2, 2022 at 4:23 PM Philippe Gerum via Xenomai
> <xenomai@xenomai.org> wrote:
>
>> -       arch_dovetail_switch_finish(leave_inband);
>> +       ti_work = READ_ONCE(current_thread_info()->flags);
>> +       arch_dovetail_switch_finish(leave_inband, ti_work);
>
> Why are you passing ti_work as parameter? AFAIU you can
> use current_thread_info()->flags directly in arch_dovetail_switch_finish().

Agreed, this affects the signature of arch_dovetail_switch_finish() for
no good reason. Besides, this patch is missing a case (task resuming
after oob -> inband transition). v2 follows (tested ok here).

-- 
Philippe.