[PATCH -tip v3 1/3] x86/percpu: Fix "const_pcpu_hot" version generation failure

[PATCH -tip v3 1/3] x86/percpu: Fix "const_pcpu_hot" version generation failure

[Uros Bizjak]

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 <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
---
v2: Use BUILD_BUG() instead of BUG().
---
 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..3859abad19ec 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -28,6 +28,7 @@
 
 #else /* ...!ASSEMBLY */
 
+#include <linux/build_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)	({ BUILD_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

[PATCH -tip v3 2/3] x86/traps: Use current_top_of_stack() helper in traps.c

[Uros Bizjak]

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 <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
---
 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

[tip: x86/percpu] x86/traps: Use current_top_of_stack() helper in traps.c

[tip-bot2 for Uros Bizjak]

The following commit has been merged into the x86/percpu branch of tip:

Commit-ID:     13408c6ae684181d53c870cceddbd3a62ae34c3e
Gitweb:        https://git.kernel.org/tip/13408c6ae684181d53c870cceddbd3a62ae34c3e
Author:        Uros Bizjak <ubizjak@gmail.com>
AuthorDate:    Mon, 04 Dec 2023 22:02:30 +01:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Mon, 11 Dec 2023 11:47:15 +01:00

x86/traps: Use current_top_of_stack() helper in traps.c

Use current_top_of_stack() helper in sync_regs() and vc_switch_off_ist()
instead of open-coding the reading of  the top_of_stack percpu variable
explicitly.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20231204210320.114429-2-ubizjak@gmail.com
---
 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 c876f1d..78b1d1a 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;
 	}
 

[PATCH -tip v3 3/3] x86/percpu: Avoid sparse warning with cast to named address space

[Uros Bizjak]

Teach sparse about __seg_fs and __seg_gs named address space
qualifiers to to avoid warnings about unexpected keyword at
the end of cast operator.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202310080853.UhMe5iWa-lkp@intel.com/
Cc: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
---
v3: Teach sparse about __seg_gs and __seg_fs qualifiers instead
    of removing these qualifiers when __CHECKER__ is defined.
---
 arch/x86/include/asm/percpu.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index 3859abad19ec..e56a37886143 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -36,6 +36,11 @@
 
 #ifdef CONFIG_CC_HAS_NAMED_AS
 
+#ifdef __CHECKER__
+#define __seg_gs		__attribute__((address_space(__seg_gs)))
+#define __seg_fs		__attribute__((address_space(__seg_fs)))
+#endif
+
 #ifdef CONFIG_X86_64
 #define __percpu_seg_override	__seg_gs
 #else
-- 
2.42.0

Re: [PATCH -tip v3 3/3] x86/percpu: Avoid sparse warning with cast to named address space

[Luc Van Oostenryck]

On Mon, Dec 04, 2023 at 10:02:31PM +0100, Uros Bizjak wrote:
> Teach sparse about __seg_fs and __seg_gs named address space
> qualifiers to to avoid warnings about unexpected keyword at
> the end of cast operator.
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202310080853.UhMe5iWa-lkp@intel.com/
> Cc: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>

Acked-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>

[tip: x86/percpu] x86/percpu: Avoid sparse warning with cast to named address space

[tip-bot2 for Uros Bizjak]

The following commit has been merged into the x86/percpu branch of tip:

Commit-ID:     3a1d3829e193c091475ceab481c5f8deab385023
Gitweb:        https://git.kernel.org/tip/3a1d3829e193c091475ceab481c5f8deab385023
Author:        Uros Bizjak <ubizjak@gmail.com>
AuthorDate:    Mon, 04 Dec 2023 22:02:31 +01:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Mon, 11 Dec 2023 11:47:15 +01:00

x86/percpu: Avoid sparse warning with cast to named address space

Teach sparse about __seg_fs and __seg_gs named address space
qualifiers to to avoid warnings about unexpected keyword at
the end of cast operator.

Reported-by: kernel test robot <lkp@intel.com>
Acked-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20231204210320.114429-3-ubizjak@gmail.com
Closes: https://lore.kernel.org/oe-kbuild-all/202310080853.UhMe5iWa-lkp@intel.com/
---
 arch/x86/include/asm/percpu.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index 3859aba..e56a378 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -36,6 +36,11 @@
 
 #ifdef CONFIG_CC_HAS_NAMED_AS
 
+#ifdef __CHECKER__
+#define __seg_gs		__attribute__((address_space(__seg_gs)))
+#define __seg_fs		__attribute__((address_space(__seg_fs)))
+#endif
+
 #ifdef CONFIG_X86_64
 #define __percpu_seg_override	__seg_gs
 #else

[tip: x86/percpu] x86/percpu: Fix "const_pcpu_hot" version generation failure

[tip-bot2 for Uros Bizjak]

The following commit has been merged into the x86/percpu branch of tip:

Commit-ID:     0e3703630bd3fead041a6bfb3a3f2a9891af6c34
Gitweb:        https://git.kernel.org/tip/0e3703630bd3fead041a6bfb3a3f2a9891af6c34
Author:        Uros Bizjak <ubizjak@gmail.com>
AuthorDate:    Mon, 04 Dec 2023 22:02:29 +01:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Mon, 11 Dec 2023 11:47:14 +01:00

x86/percpu: Fix "const_pcpu_hot" version generation failure

Version generation for "const_pcpu_hot" symbol failed because genksyms
doesn't know the __seg_gs keyword. Effectively 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.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20231204210320.114429-1-ubizjak@gmail.com
---
 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 9fbd7cb..c8c5674 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 0f12b20..3859aba 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -28,6 +28,7 @@
 
 #else /* ...!ASSEMBLY */
 
+#include <linux/build_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)	({ BUILD_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 f20e876..a94a857 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -519,7 +519,7 @@ 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);
 }