| Message ID | 20220726073750.3219117-3-kaleshsingh@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM nVHE Hypervisor stack unwinder | expand |
On Tue, 26 Jul 2022 08:37:35 +0100, Kalesh Singh <kaleshsingh@google.com> wrote: > > Move common on_accessible_stack checks to stacktrace/common.h. This is > used in the implementation of the nVHE hypervisor unwinder later in > this series. > > Signed-off-by: Kalesh Singh <kaleshsingh@google.com> > Reviewed-by: Fuad Tabba <tabba@google.com> > Reviewed-by: Mark Brown <broonie@kernel.org> > Tested-by: Fuad Tabba <tabba@google.com> > --- > > Changes in v6: > - Add Fuad's Tested-by tag > > Changes in v5: > - Add Reviewed-by tags from Mark Brown and Fuad > - Remove random whitespace change, per Mark Brown > > arch/arm64/include/asm/stacktrace.h | 6 ++---- > arch/arm64/include/asm/stacktrace/common.h | 18 ++++++++++++++++++ > 2 files changed, 20 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h > index 79f455b37c84..43f4b4a6d383 100644 > --- a/arch/arm64/include/asm/stacktrace.h > +++ b/arch/arm64/include/asm/stacktrace.h > @@ -65,8 +65,8 @@ static inline bool on_accessible_stack(const struct task_struct *tsk, > unsigned long sp, unsigned long size, > struct stack_info *info) > { > - if (info) > - info->type = STACK_TYPE_UNKNOWN; > + if (on_accessible_stack_common(tsk, sp, size, info)) > + return true; > > if (on_task_stack(tsk, sp, size, info)) > return true; > @@ -74,8 +74,6 @@ static inline bool on_accessible_stack(const struct task_struct *tsk, > return false; > if (on_irq_stack(sp, size, info)) > return true; > - if (on_overflow_stack(sp, size, info)) > - return true; > if (on_sdei_stack(sp, size, info)) > return true; > > diff --git a/arch/arm64/include/asm/stacktrace/common.h b/arch/arm64/include/asm/stacktrace/common.h > index 64ae4f6b06fe..f58b786460d3 100644 > --- a/arch/arm64/include/asm/stacktrace/common.h > +++ b/arch/arm64/include/asm/stacktrace/common.h > @@ -62,6 +62,9 @@ struct unwind_state { > struct task_struct *task; > }; > > +static inline bool on_overflow_stack(unsigned long sp, unsigned long size, > + struct stack_info *info); > + > static inline bool on_stack(unsigned long sp, unsigned long size, > unsigned long low, unsigned long high, > enum stack_type type, struct stack_info *info) > @@ -80,6 +83,21 @@ static inline bool on_stack(unsigned long sp, unsigned long size, > return true; > } > > +static inline bool on_accessible_stack_common(const struct task_struct *tsk, > + unsigned long sp, > + unsigned long size, > + struct stack_info *info) > +{ > + if (info) > + info->type = STACK_TYPE_UNKNOWN; > + > + /* > + * Both the kernel and nvhe hypervisor make use of > + * an overflow_stack > + */ > + return on_overflow_stack(sp, size, info); > +} on_accessible_stack has the following comment: /* * We can only safely access per-cpu stacks from current in a non-preemptible * context. */ With this change, I don't think we satisfy this requirement anymore, as we're checking the overflow stack *before* the preemptible check, which is a big change in behaviour. The hypervisor doesn't have this requirement: the unwinding is either done out of context (nVHE, where EL1 unwinds EL2) or in a non-preemptible section (pKVM, where the whole thing is non-preemptible). But the kernel is usually preemptible, so this patch needs fixing. I'll see if I can address it locally (I'm currently moving things around, stay tuned). Thanks, M.
On Tue, Jul 26, 2022 at 9:01 AM Marc Zyngier <maz@kernel.org> wrote: > > On Tue, 26 Jul 2022 08:37:35 +0100, > Kalesh Singh <kaleshsingh@google.com> wrote: > > > > Move common on_accessible_stack checks to stacktrace/common.h. This is > > used in the implementation of the nVHE hypervisor unwinder later in > > this series. > > > > Signed-off-by: Kalesh Singh <kaleshsingh@google.com> > > Reviewed-by: Fuad Tabba <tabba@google.com> > > Reviewed-by: Mark Brown <broonie@kernel.org> > > Tested-by: Fuad Tabba <tabba@google.com> > > --- > > > > Changes in v6: > > - Add Fuad's Tested-by tag > > > > Changes in v5: > > - Add Reviewed-by tags from Mark Brown and Fuad > > - Remove random whitespace change, per Mark Brown > > > > arch/arm64/include/asm/stacktrace.h | 6 ++---- > > arch/arm64/include/asm/stacktrace/common.h | 18 ++++++++++++++++++ > > 2 files changed, 20 insertions(+), 4 deletions(-) > > > > diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h > > index 79f455b37c84..43f4b4a6d383 100644 > > --- a/arch/arm64/include/asm/stacktrace.h > > +++ b/arch/arm64/include/asm/stacktrace.h > > @@ -65,8 +65,8 @@ static inline bool on_accessible_stack(const struct task_struct *tsk, > > unsigned long sp, unsigned long size, > > struct stack_info *info) > > { > > - if (info) > > - info->type = STACK_TYPE_UNKNOWN; > > + if (on_accessible_stack_common(tsk, sp, size, info)) > > + return true; > > > > if (on_task_stack(tsk, sp, size, info)) > > return true; > > @@ -74,8 +74,6 @@ static inline bool on_accessible_stack(const struct task_struct *tsk, > > return false; > > if (on_irq_stack(sp, size, info)) > > return true; > > - if (on_overflow_stack(sp, size, info)) > > - return true; > > if (on_sdei_stack(sp, size, info)) > > return true; > > > > diff --git a/arch/arm64/include/asm/stacktrace/common.h b/arch/arm64/include/asm/stacktrace/common.h > > index 64ae4f6b06fe..f58b786460d3 100644 > > --- a/arch/arm64/include/asm/stacktrace/common.h > > +++ b/arch/arm64/include/asm/stacktrace/common.h > > @@ -62,6 +62,9 @@ struct unwind_state { > > struct task_struct *task; > > }; > > > > +static inline bool on_overflow_stack(unsigned long sp, unsigned long size, > > + struct stack_info *info); > > + > > static inline bool on_stack(unsigned long sp, unsigned long size, > > unsigned long low, unsigned long high, > > enum stack_type type, struct stack_info *info) > > @@ -80,6 +83,21 @@ static inline bool on_stack(unsigned long sp, unsigned long size, > > return true; > > } > > > > +static inline bool on_accessible_stack_common(const struct task_struct *tsk, > > + unsigned long sp, > > + unsigned long size, > > + struct stack_info *info) > > +{ > > + if (info) > > + info->type = STACK_TYPE_UNKNOWN; > > + > > + /* > > + * Both the kernel and nvhe hypervisor make use of > > + * an overflow_stack > > + */ > > + return on_overflow_stack(sp, size, info); > > +} > > on_accessible_stack has the following comment: > > /* > * We can only safely access per-cpu stacks from current in a non-preemptible > * context. > */ > > With this change, I don't think we satisfy this requirement anymore, > as we're checking the overflow stack *before* the preemptible check, > which is a big change in behaviour. > > The hypervisor doesn't have this requirement: the unwinding is either > done out of context (nVHE, where EL1 unwinds EL2) or in a > non-preemptible section (pKVM, where the whole thing is > non-preemptible). But the kernel is usually preemptible, so this patch > needs fixing. > > I'll see if I can address it locally (I'm currently moving things > around, stay tuned). Hi Marc, You are right it changes the order of the checks. I think the simplest way then is to drop this patch, and replace uses of on_accessible _stack_common(). Thanks, Kalesh > > Thanks, > > M. > > -- > Without deviation from the norm, progress is not possible.
diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h index 79f455b37c84..43f4b4a6d383 100644 --- a/arch/arm64/include/asm/stacktrace.h +++ b/arch/arm64/include/asm/stacktrace.h @@ -65,8 +65,8 @@ static inline bool on_accessible_stack(const struct task_struct *tsk, unsigned long sp, unsigned long size, struct stack_info *info) { - if (info) - info->type = STACK_TYPE_UNKNOWN; + if (on_accessible_stack_common(tsk, sp, size, info)) + return true; if (on_task_stack(tsk, sp, size, info)) return true; @@ -74,8 +74,6 @@ static inline bool on_accessible_stack(const struct task_struct *tsk, return false; if (on_irq_stack(sp, size, info)) return true; - if (on_overflow_stack(sp, size, info)) - return true; if (on_sdei_stack(sp, size, info)) return true; diff --git a/arch/arm64/include/asm/stacktrace/common.h b/arch/arm64/include/asm/stacktrace/common.h index 64ae4f6b06fe..f58b786460d3 100644 --- a/arch/arm64/include/asm/stacktrace/common.h +++ b/arch/arm64/include/asm/stacktrace/common.h @@ -62,6 +62,9 @@ struct unwind_state { struct task_struct *task; }; +static inline bool on_overflow_stack(unsigned long sp, unsigned long size, + struct stack_info *info); + static inline bool on_stack(unsigned long sp, unsigned long size, unsigned long low, unsigned long high, enum stack_type type, struct stack_info *info) @@ -80,6 +83,21 @@ static inline bool on_stack(unsigned long sp, unsigned long size, return true; } +static inline bool on_accessible_stack_common(const struct task_struct *tsk, + unsigned long sp, + unsigned long size, + struct stack_info *info) +{ + if (info) + info->type = STACK_TYPE_UNKNOWN; + + /* + * Both the kernel and nvhe hypervisor make use of + * an overflow_stack + */ + return on_overflow_stack(sp, size, info); +} + static inline void unwind_init_common(struct unwind_state *state, struct task_struct *task) {