Version generation for "const_pcpu_hot" symbol failed because genksyms
doesn't know the __seg_gs keyword. Revert commit 4604c052b84d
"x86/percpu: Declare const_pcpu_hot as extern const variable" and
use this_cpu_read_const instead to avoid "sparse: dereference of
noderef expression" warning when reading const_pcpu_hot.
Cc: Andy Lutomirski <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Signed-off-by: Uros Bizjak <[email protected]>
---
arch/x86/include/asm/current.h | 5 +++--
arch/x86/include/asm/percpu.h | 7 +++++++
arch/x86/include/asm/processor.h | 2 +-
3 files changed, 11 insertions(+), 3 deletions(-)
diff --git a/arch/x86/include/asm/current.h b/arch/x86/include/asm/current.h
index 9fbd7cb2dc86..c8c5674d69f6 100644
--- a/arch/x86/include/asm/current.h
+++ b/arch/x86/include/asm/current.h
@@ -37,12 +37,13 @@ static_assert(sizeof(struct pcpu_hot) == 64);
DECLARE_PER_CPU_ALIGNED(struct pcpu_hot, pcpu_hot);
/* const-qualified alias to pcpu_hot, aliased by linker. */
-extern const struct pcpu_hot __percpu_seg_override const_pcpu_hot;
+DECLARE_PER_CPU_ALIGNED(const struct pcpu_hot __percpu_seg_override,
+ const_pcpu_hot);
static __always_inline struct task_struct *get_current(void)
{
if (IS_ENABLED(CONFIG_USE_X86_SEG_SUPPORT))
- return const_pcpu_hot.current_task;
+ return this_cpu_read_const(const_pcpu_hot.current_task);
return this_cpu_read_stable(pcpu_hot.current_task);
}
diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index 0f12b2004b94..7f6e978e21b1 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -28,6 +28,7 @@
#else /* ...!ASSEMBLY */
+#include <linux/bug.h>
#include <linux/kernel.h>
#include <linux/stringify.h>
@@ -462,6 +463,7 @@ do { \
#define this_cpu_write_8(pcp, val) __raw_cpu_write(volatile, pcp, val)
#endif
+#define this_cpu_read_const(pcp) __raw_cpu_read(, pcp)
#else /* CONFIG_USE_X86_SEG_SUPPORT */
#define raw_cpu_read_1(pcp) percpu_from_op(1, , "mov", pcp)
@@ -486,6 +488,11 @@ do { \
#define this_cpu_write_8(pcp, val) percpu_to_op(8, volatile, "mov", (pcp), val)
#endif
+/*
+ * The generic per-cpu infrastrucutre is not suitable for
+ * reading const-qualified variables.
+ */
+#define this_cpu_read_const(pcp) ({ BUG(); (typeof(pcp))0; })
#endif /* CONFIG_USE_X86_SEG_SUPPORT */
#define raw_cpu_add_1(pcp, val) percpu_add_op(1, , (pcp), val)
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 061aa86b4662..1188e8bf76a2 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -534,7 +534,7 @@ static __always_inline unsigned long current_top_of_stack(void)
* entry trampoline.
*/
if (IS_ENABLED(CONFIG_USE_X86_SEG_SUPPORT))
- return const_pcpu_hot.top_of_stack;
+ return this_cpu_read_const(const_pcpu_hot.top_of_stack);
return this_cpu_read_stable(pcpu_hot.top_of_stack);
}
--
2.42.0
Use current_top_of_stack() helper in sync_regs() and vc_switch_off_ist()
instead of reading top_of_stack percpu variable explicitly.
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Signed-off-by: Uros Bizjak <[email protected]>
---
arch/x86/kernel/traps.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index c876f1d36a81..78b1d1a6ed2c 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -772,7 +772,7 @@ DEFINE_IDTENTRY_RAW(exc_int3)
*/
asmlinkage __visible noinstr struct pt_regs *sync_regs(struct pt_regs *eregs)
{
- struct pt_regs *regs = (struct pt_regs *)this_cpu_read(pcpu_hot.top_of_stack) - 1;
+ struct pt_regs *regs = (struct pt_regs *)current_top_of_stack() - 1;
if (regs != eregs)
*regs = *eregs;
return regs;
@@ -790,7 +790,7 @@ asmlinkage __visible noinstr struct pt_regs *vc_switch_off_ist(struct pt_regs *r
* trust it and switch to the current kernel stack
*/
if (ip_within_syscall_gap(regs)) {
- sp = this_cpu_read(pcpu_hot.top_of_stack);
+ sp = current_top_of_stack();
goto sync;
}
--
2.42.0
Currently sparse does not know about __seg_fs and __seg_fs named
address space qualifiers. Avoid thousands of warnings about unexpected
keyword at the end of cast operator by removing named address space
qualifier from __my_cpu_type() when __CHECKER__ is defined.
Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Signed-off-by: Uros Bizjak <[email protected]>
---
arch/x86/include/asm/percpu.h | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index 7f6e978e21b1..07ee2aedb1f6 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -96,6 +96,15 @@
#endif /* CONFIG_SMP */
+/*
+ * FIXME: Drop this hack once sparse learns how to ignore
+ * __seg_fs and __seg_gs named address space qualifiers.
+ */
+#ifdef __CHECKER__
+#undef __percpu_seg_override
+#define __percpu_seg_override
+#endif
+
#define __my_cpu_type(var) typeof(var) __percpu_seg_override
#define __my_cpu_ptr(ptr) (__my_cpu_type(*ptr) *)(uintptr_t)(ptr)
#define __my_cpu_var(var) (*__my_cpu_ptr(&var))
--
2.42.0
On Mon, 4 Dec 2023 at 07:12, Uros Bizjak <[email protected]> wrote:
>
> +/*
> + * The generic per-cpu infrastrucutre is not suitable for
> + * reading const-qualified variables.
> + */
> +#define this_cpu_read_const(pcp) ({ BUG(); (typeof(pcp))0; })
NAK. Absolutely not.
No way in hell is it acceptable to make this a run-time BUG. If it
doesn't work, it needs to be a compile failure. End of story.
Linus
On Sun, Dec 3, 2023 at 11:19 PM Linus Torvalds
<[email protected]> wrote:
>
> On Mon, 4 Dec 2023 at 07:12, Uros Bizjak <[email protected]> wrote:
> >
> > +/*
> > + * The generic per-cpu infrastrucutre is not suitable for
> > + * reading const-qualified variables.
> > + */
> > +#define this_cpu_read_const(pcp) ({ BUG(); (typeof(pcp))0; })
>
> NAK. Absolutely not.
>
> No way in hell is it acceptable to make this a run-time BUG. If it
> doesn't work, it needs to be a compile failure. End of story.
Thanks - BUILD_BUG() also works here and is indeed more appropriate:
/**
* BUILD_BUG - break compile if used.
*
* If you have some code that you expect the compiler to eliminate at
* build time, you should use BUILD_BUG to detect if it is
* unexpectedly used.
*/
v2 is in testing.
Thanks,
Uros.