[PATCH v7 00/10] Improve signal performance on PPC64 with KUAP

[PATCH v7 00/10] Improve signal performance on PPC64 with KUAP

[Christopher M. Riedl]

As reported by Anton, there is a large penalty to signal handling
performance on radix systems using KUAP. The signal handling code
performs many user access operations, each of which needs to switch the
KUAP permissions bit to open and then close user access. This involves a
costly 'mtspr' operation [0].

There is existing work done on x86 and by Christophe Leroy for PPC32 to
instead open up user access in "blocks" using user_*_access_{begin,end}.
We can do the same in PPC64 to bring performance back up on KUAP-enabled
radix and now also hash MMU systems [1].

Hash MMU KUAP support along with uaccess flush has landed in linuxppc/next
since the last revision. This series also provides a large benefit on hash
with KUAP. However, in the hash implementation of KUAP the user AMR is
always restored during system_call_exception() which cannot be avoided.
Fewer user access switches naturally also result in less uaccess flushing.

The first two patches add some needed 'unsafe' versions of copy-from
functions. While these do not make use of asm-goto they still allow for
avoiding the repeated uaccess switches.

The third patch moves functions called by setup_sigcontext() into a new
prepare_setup_sigcontext() to simplify converting setup_sigcontext()
into an 'unsafe' version which assumes an open uaccess window later.

The fourth and fifths patches clean-up some of the Transactional Memory
ifdef stuff to simplify using uaccess blocks later.

The next two patches rewrite some of the signal64 helper functions to
be 'unsafe'. Finally, the last three patches update the main signal
handling functions to make use of the new 'unsafe' helpers and eliminate
some additional uaccess switching.

I used the will-it-scale signal1 benchmark to measure and compare
performance [2]. The below results are from running a minimal
kernel+initramfs QEMU/KVM guest on a POWER9 Blackbird:

	signal1_threads -t1 -s10

	|                              | hash   | radix  |
	| ---------------------------- | ------ | ------ |
	| linuxppc/next                | 117898 | 135884 |
	| linuxppc/next w/o KUAP+KUEP  | 225502 | 227509 |
	| unsafe-signal64              | 195351 | 230922 |

[0]: https://github.com/linuxppc/issues/issues/277
[1]: https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=196278
[2]: https://github.com/antonblanchard/will-it-scale/blob/master/tests/signal1.c

v7:	* Address feedback from Christophe Leroy

v6:	* Rebase on latest linuxppc/next and address feedback comments from
	  Daniel Axtens and friends (also pick up some Reviewed-by tags)
	* Simplify __get_user_sigset(), fix sparse warnings, and use it
	  in ppc32 signal handling
	* Remove ctx_has_vsx_region arg to prepare_setup_sigcontext()
	* Remove local buffer in copy_{fpr,vsx}_from_user()
	* Rework the TM ifdefery-removal and remove one of the ifdef
	  pairs altogether

v5:	* Use sizeof(buf) in copy_{vsx,fpr}_from_user() (Thanks David Laight)
	* Rebase on latest linuxppc/next

v4:	* Fix issues identified by Christophe Leroy (Thanks for review)
	* Use __get_user() directly to copy the 8B sigset_t

v3:	* Rebase on latest linuxppc/next
	* Reword confusing commit messages
	* Add missing comma in macro in signal.h which broke compiles without
	  CONFIG_ALTIVEC
	* Validate hash KUAP signal performance improvements

v2:	* Rebase on latest linuxppc/next + Christophe Leroy's PPC32
	  signal series
	* Simplify/remove TM ifdefery similar to PPC32 series and clean
	  up the uaccess begin/end calls
	* Isolate non-inline functions so they are not called when
	  uaccess window is open

Christopher M. Riedl (8):
  powerpc/uaccess: Add unsafe_copy_from_user()
  powerpc/signal: Add unsafe_copy_{vsx,fpr}_from_user()
  powerpc/signal64: Remove non-inline calls from setup_sigcontext()
  powerpc: Reference parameter in MSR_TM_ACTIVE() macro
  powerpc/signal64: Remove TM ifdefery in middle of if/else block
  powerpc/signal64: Replace setup_sigcontext() w/
    unsafe_setup_sigcontext()
  powerpc/signal64: Replace restore_sigcontext() w/
    unsafe_restore_sigcontext()
  powerpc/signal: Use __get_user() to copy sigset_t

Daniel Axtens (2):
  powerpc/signal64: Rewrite handle_rt_signal64() to minimise uaccess
    switches
  powerpc/signal64: Rewrite rt_sigreturn() to minimise uaccess switches

 arch/powerpc/include/asm/reg.h     |   2 +-
 arch/powerpc/include/asm/uaccess.h |  21 ++
 arch/powerpc/kernel/process.c      |   3 +-
 arch/powerpc/kernel/signal.h       |  33 +++
 arch/powerpc/kernel/signal_32.c    |   2 +-
 arch/powerpc/kernel/signal_64.c    | 316 +++++++++++++++++------------
 6 files changed, 246 insertions(+), 131 deletions(-)

-- 
2.26.1

[PATCH v7 01/10] powerpc/uaccess: Add unsafe_copy_from_user()

[Christopher M. Riedl]

Use the same approach as unsafe_copy_to_user() but instead call
unsafe_get_user() in a loop.

Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
---
v7:	* Change implementation to call unsafe_get_user() and remove
	  dja's 'Reviewed-by' tag
---
 arch/powerpc/include/asm/uaccess.h | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index 78e2a3990eab..ef5978b73a8d 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -487,6 +487,27 @@ user_write_access_begin(const void __user *ptr, size_t len)
 #define unsafe_put_user(x, p, e) \
 	__unsafe_put_user_goto((__typeof__(*(p)))(x), (p), sizeof(*(p)), e)
 
+#define unsafe_copy_from_user(d, s, l, e) \
+do {											\
+	u8 *_dst = (u8 *)(d);								\
+	const u8 __user *_src = (const u8 __user *)(s);					\
+	size_t _len = (l);								\
+	int _i;										\
+											\
+	for (_i = 0; _i < (_len & ~(sizeof(long) - 1)); _i += sizeof(long))		\
+		unsafe_get_user(*(long *)(_dst + _i), (long __user *)(_src + _i), e);	\
+	if (IS_ENABLED(CONFIG_PPC64) && (_len & 4)) {					\
+		unsafe_get_user(*(u32 *)(_dst + _i), (u32 __user *)(_src + _i), e);	\
+		_i += 4;								\
+	}										\
+	if (_len & 2) {									\
+		unsafe_get_user(*(u16 *)(_dst + _i), (u16 __user *)(_src + _i), e);	\
+		_i += 2;								\
+	}										\
+	if (_len & 1)									\
+		unsafe_get_user(*(u8 *)(_dst + _i), (u8 __user *)(_src + _i), e);	\
+} while (0)
+
 #define unsafe_copy_to_user(d, s, l, e) \
 do {									\
 	u8 __user *_dst = (u8 __user *)(d);				\
-- 
2.26.1

[PATCH v7 02/10] powerpc/signal: Add unsafe_copy_{vsx, fpr}_from_user()

[Christopher M. Riedl]

Reuse the "safe" implementation from signal.c but call unsafe_get_user()
directly in a loop to avoid the intermediate copy into a local buffer.

Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
Reviewed-by: Daniel Axtens <dja@axtens.net>
---
 arch/powerpc/kernel/signal.h | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/arch/powerpc/kernel/signal.h b/arch/powerpc/kernel/signal.h
index 2559a681536e..d8dd76b1dc94 100644
--- a/arch/powerpc/kernel/signal.h
+++ b/arch/powerpc/kernel/signal.h
@@ -53,6 +53,26 @@ unsigned long copy_ckfpr_from_user(struct task_struct *task, void __user *from);
 				&buf[i], label);\
 } while (0)
 
+#define unsafe_copy_fpr_from_user(task, from, label)	do {		\
+	struct task_struct *__t = task;					\
+	u64 __user *buf = (u64 __user *)from;				\
+	int i;								\
+									\
+	for (i = 0; i < ELF_NFPREG - 1; i++)				\
+		unsafe_get_user(__t->thread.TS_FPR(i), &buf[i], label); \
+	unsafe_get_user(__t->thread.fp_state.fpscr, &buf[i], label);	\
+} while (0)
+
+#define unsafe_copy_vsx_from_user(task, from, label)	do {		\
+	struct task_struct *__t = task;					\
+	u64 __user *buf = (u64 __user *)from;				\
+	int i;								\
+									\
+	for (i = 0; i < ELF_NVSRHALFREG ; i++)				\
+		unsafe_get_user(__t->thread.fp_state.fpr[i][TS_VSRLOWOFFSET], \
+				&buf[i], label);			\
+} while (0)
+
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 #define unsafe_copy_ckfpr_to_user(to, task, label)	do {		\
 	struct task_struct *__t = task;					\
@@ -80,6 +100,10 @@ unsigned long copy_ckfpr_from_user(struct task_struct *task, void __user *from);
 	unsafe_copy_to_user(to, (task)->thread.fp_state.fpr,	\
 			    ELF_NFPREG * sizeof(double), label)
 
+#define unsafe_copy_fpr_from_user(task, from, label)			\
+	unsafe_copy_from_user((task)->thread.fp_state.fpr, from,	\
+			    ELF_NFPREG * sizeof(double), label)
+
 static inline unsigned long
 copy_fpr_to_user(void __user *to, struct task_struct *task)
 {
@@ -115,6 +139,8 @@ copy_ckfpr_from_user(struct task_struct *task, void __user *from)
 #else
 #define unsafe_copy_fpr_to_user(to, task, label) do { } while (0)
 
+#define unsafe_copy_fpr_from_user(task, from, label) do { } while (0)
+
 static inline unsigned long
 copy_fpr_to_user(void __user *to, struct task_struct *task)
 {
-- 
2.26.1

[PATCH v7 03/10] powerpc/signal64: Remove non-inline calls from setup_sigcontext()

[Christopher M. Riedl]

The majority of setup_sigcontext() can be refactored to execute in an
"unsafe" context assuming an open uaccess window except for some
non-inline function calls. Move these out into a separate
prepare_setup_sigcontext() function which must be called first and
before opening up a uaccess window. Non-inline function calls should be
avoided during a uaccess window for a few reasons:

	- KUAP should be enabled for as much kernel code as possible.
	  Opening a uaccess window disables KUAP which means any code
	  executed during this time contributes to a potential attack
	  surface.

	- Non-inline functions default to traceable which means they are
	  instrumented for ftrace. This adds more code which could run
	  with KUAP disabled.

	- Powerpc does not currently support the objtool UACCESS checks.
	  All code running with uaccess must be audited manually which
	  means: less code -> less work -> fewer problems (in theory).

A follow-up commit converts setup_sigcontext() to be "unsafe".

Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
---
 arch/powerpc/kernel/signal_64.c | 32 +++++++++++++++++++++-----------
 1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index f9e4a1ac440f..6ca546192cbf 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -79,6 +79,24 @@ static elf_vrreg_t __user *sigcontext_vmx_regs(struct sigcontext __user *sc)
 }
 #endif
 
+static void prepare_setup_sigcontext(struct task_struct *tsk)
+{
+#ifdef CONFIG_ALTIVEC
+	/* save altivec registers */
+	if (tsk->thread.used_vr)
+		flush_altivec_to_thread(tsk);
+	if (cpu_has_feature(CPU_FTR_ALTIVEC))
+		tsk->thread.vrsave = mfspr(SPRN_VRSAVE);
+#endif /* CONFIG_ALTIVEC */
+
+	flush_fp_to_thread(tsk);
+
+#ifdef CONFIG_VSX
+	if (tsk->thread.used_vsr)
+		flush_vsx_to_thread(tsk);
+#endif /* CONFIG_VSX */
+}
+
 /*
  * Set up the sigcontext for the signal frame.
  */
@@ -97,7 +115,6 @@ static long setup_sigcontext(struct sigcontext __user *sc,
 	 */
 #ifdef CONFIG_ALTIVEC
 	elf_vrreg_t __user *v_regs = sigcontext_vmx_regs(sc);
-	unsigned long vrsave;
 #endif
 	struct pt_regs *regs = tsk->thread.regs;
 	unsigned long msr = regs->msr;
@@ -112,7 +129,6 @@ static long setup_sigcontext(struct sigcontext __user *sc,
 
 	/* save altivec registers */
 	if (tsk->thread.used_vr) {
-		flush_altivec_to_thread(tsk);
 		/* Copy 33 vec registers (vr0..31 and vscr) to the stack */
 		err |= __copy_to_user(v_regs, &tsk->thread.vr_state,
 				      33 * sizeof(vector128));
@@ -124,17 +140,10 @@ static long setup_sigcontext(struct sigcontext __user *sc,
 	/* We always copy to/from vrsave, it's 0 if we don't have or don't
 	 * use altivec.
 	 */
-	vrsave = 0;
-	if (cpu_has_feature(CPU_FTR_ALTIVEC)) {
-		vrsave = mfspr(SPRN_VRSAVE);
-		tsk->thread.vrsave = vrsave;
-	}
-
-	err |= __put_user(vrsave, (u32 __user *)&v_regs[33]);
+	err |= __put_user(tsk->thread.vrsave, (u32 __user *)&v_regs[33]);
 #else /* CONFIG_ALTIVEC */
 	err |= __put_user(0, &sc->v_regs);
 #endif /* CONFIG_ALTIVEC */
-	flush_fp_to_thread(tsk);
 	/* copy fpr regs and fpscr */
 	err |= copy_fpr_to_user(&sc->fp_regs, tsk);
 
@@ -150,7 +159,6 @@ static long setup_sigcontext(struct sigcontext __user *sc,
 	 * VMX data.
 	 */
 	if (tsk->thread.used_vsr && ctx_has_vsx_region) {
-		flush_vsx_to_thread(tsk);
 		v_regs += ELF_NVRREG;
 		err |= copy_vsx_to_user(v_regs, tsk);
 		/* set MSR_VSX in the MSR value in the frame to
@@ -655,6 +663,7 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
 		ctx_has_vsx_region = 1;
 
 	if (old_ctx != NULL) {
+		prepare_setup_sigcontext(current);
 		if (!access_ok(old_ctx, ctx_size)
 		    || setup_sigcontext(&old_ctx->uc_mcontext, current, 0, NULL, 0,
 					ctx_has_vsx_region)
@@ -842,6 +851,7 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
 #endif
 	{
 		err |= __put_user(0, &frame->uc.uc_link);
+		prepare_setup_sigcontext(tsk);
 		err |= setup_sigcontext(&frame->uc.uc_mcontext, tsk, ksig->sig,
 					NULL, (unsigned long)ksig->ka.sa.sa_handler,
 					1);
-- 
2.26.1

[PATCH v7 04/10] powerpc: Reference parameter in MSR_TM_ACTIVE() macro

[Christopher M. Riedl]

Unlike the other MSR_TM_* macros, MSR_TM_ACTIVE does not reference or
use its parameter unless CONFIG_PPC_TRANSACTIONAL_MEM is defined. This
causes an 'unused variable' compile warning unless the variable is also
guarded with CONFIG_PPC_TRANSACTIONAL_MEM.

Reference but do nothing with the argument in the macro to avoid a
potential compile warning.

Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
Reviewed-by: Daniel Axtens <dja@axtens.net>
---
 arch/powerpc/include/asm/reg.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index da103e92c112..1be20bc8dce2 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -124,7 +124,7 @@
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 #define MSR_TM_ACTIVE(x) (((x) & MSR_TS_MASK) != 0) /* Transaction active? */
 #else
-#define MSR_TM_ACTIVE(x) 0
+#define MSR_TM_ACTIVE(x) ((void)(x), 0)
 #endif
 
 #if defined(CONFIG_PPC_BOOK3S_64)
-- 
2.26.1

[PATCH v7 05/10] powerpc/signal64: Remove TM ifdefery in middle of if/else block

[Christopher M. Riedl]

Both rt_sigreturn() and handle_rt_signal_64() contain TM-related ifdefs
which break-up an if/else block. Provide stubs for the ifdef-guarded TM
functions and remove the need for an ifdef in rt_sigreturn().

Rework the remaining TM ifdef in handle_rt_signal64() similar to
commit f1cf4f93de2f ("powerpc/signal32: Remove ifdefery in middle of if/else").

Unlike in the commit for ppc32, the ifdef can't be removed entirely
since uc_transact in sigframe depends on CONFIG_PPC_TRANSACTIONAL_MEM.

Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
---
 arch/powerpc/kernel/process.c   |   3 +-
 arch/powerpc/kernel/signal_64.c | 102 ++++++++++++++++----------------
 2 files changed, 54 insertions(+), 51 deletions(-)

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 924d023dad0a..08c3fbe45921 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1117,9 +1117,10 @@ void restore_tm_state(struct pt_regs *regs)
 	regs->msr |= msr_diff;
 }
 
-#else
+#else /* !CONFIG_PPC_TRANSACTIONAL_MEM */
 #define tm_recheckpoint_new_task(new)
 #define __switch_to_tm(prev, new)
+void tm_reclaim_current(uint8_t cause) {}
 #endif /* CONFIG_PPC_TRANSACTIONAL_MEM */
 
 static inline void save_sprs(struct thread_struct *t)
diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index 6ca546192cbf..bd8d210c9115 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -594,6 +594,12 @@ static long restore_tm_sigcontexts(struct task_struct *tsk,
 
 	return err;
 }
+#else /* !CONFIG_PPC_TRANSACTIONAL_MEM */
+static long restore_tm_sigcontexts(struct task_struct *tsk, struct sigcontext __user *sc,
+				   struct sigcontext __user *tm_sc)
+{
+	return -EINVAL;
+}
 #endif
 
 /*
@@ -710,9 +716,7 @@ SYSCALL_DEFINE0(rt_sigreturn)
 	struct pt_regs *regs = current_pt_regs();
 	struct ucontext __user *uc = (struct ucontext __user *)regs->gpr[1];
 	sigset_t set;
-#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 	unsigned long msr;
-#endif
 
 	/* Always make any pending restarted system calls return -EINTR */
 	current->restart_block.fn = do_no_restart_syscall;
@@ -724,48 +728,50 @@ SYSCALL_DEFINE0(rt_sigreturn)
 		goto badframe;
 	set_current_blocked(&set);
 
-#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
-	/*
-	 * If there is a transactional state then throw it away.
-	 * The purpose of a sigreturn is to destroy all traces of the
-	 * signal frame, this includes any transactional state created
-	 * within in. We only check for suspended as we can never be
-	 * active in the kernel, we are active, there is nothing better to
-	 * do than go ahead and Bad Thing later.
-	 * The cause is not important as there will never be a
-	 * recheckpoint so it's not user visible.
-	 */
-	if (MSR_TM_SUSPENDED(mfmsr()))
-		tm_reclaim_current(0);
+	if (IS_ENABLED(CONFIG_PPC_TRANSACTIONAL_MEM)) {
+		/*
+		 * If there is a transactional state then throw it away.
+		 * The purpose of a sigreturn is to destroy all traces of the
+		 * signal frame, this includes any transactional state created
+		 * within in. We only check for suspended as we can never be
+		 * active in the kernel, we are active, there is nothing better to
+		 * do than go ahead and Bad Thing later.
+		 * The cause is not important as there will never be a
+		 * recheckpoint so it's not user visible.
+		 */
+		if (MSR_TM_SUSPENDED(mfmsr()))
+			tm_reclaim_current(0);
 
-	/*
-	 * Disable MSR[TS] bit also, so, if there is an exception in the
-	 * code below (as a page fault in copy_ckvsx_to_user()), it does
-	 * not recheckpoint this task if there was a context switch inside
-	 * the exception.
-	 *
-	 * A major page fault can indirectly call schedule(). A reschedule
-	 * process in the middle of an exception can have a side effect
-	 * (Changing the CPU MSR[TS] state), since schedule() is called
-	 * with the CPU MSR[TS] disable and returns with MSR[TS]=Suspended
-	 * (switch_to() calls tm_recheckpoint() for the 'new' process). In
-	 * this case, the process continues to be the same in the CPU, but
-	 * the CPU state just changed.
-	 *
-	 * This can cause a TM Bad Thing, since the MSR in the stack will
-	 * have the MSR[TS]=0, and this is what will be used to RFID.
-	 *
-	 * Clearing MSR[TS] state here will avoid a recheckpoint if there
-	 * is any process reschedule in kernel space. The MSR[TS] state
-	 * does not need to be saved also, since it will be replaced with
-	 * the MSR[TS] that came from user context later, at
-	 * restore_tm_sigcontexts.
-	 */
-	regs->msr &= ~MSR_TS_MASK;
+		/*
+		 * Disable MSR[TS] bit also, so, if there is an exception in the
+		 * code below (as a page fault in copy_ckvsx_to_user()), it does
+		 * not recheckpoint this task if there was a context switch inside
+		 * the exception.
+		 *
+		 * A major page fault can indirectly call schedule(). A reschedule
+		 * process in the middle of an exception can have a side effect
+		 * (Changing the CPU MSR[TS] state), since schedule() is called
+		 * with the CPU MSR[TS] disable and returns with MSR[TS]=Suspended
+		 * (switch_to() calls tm_recheckpoint() for the 'new' process). In
+		 * this case, the process continues to be the same in the CPU, but
+		 * the CPU state just changed.
+		 *
+		 * This can cause a TM Bad Thing, since the MSR in the stack will
+		 * have the MSR[TS]=0, and this is what will be used to RFID.
+		 *
+		 * Clearing MSR[TS] state here will avoid a recheckpoint if there
+		 * is any process reschedule in kernel space. The MSR[TS] state
+		 * does not need to be saved also, since it will be replaced with
+		 * the MSR[TS] that came from user context later, at
+		 * restore_tm_sigcontexts.
+		 */
+		regs->msr &= ~MSR_TS_MASK;
 
-	if (__get_user(msr, &uc->uc_mcontext.gp_regs[PT_MSR]))
-		goto badframe;
-	if (MSR_TM_ACTIVE(msr)) {
+		if (__get_user(msr, &uc->uc_mcontext.gp_regs[PT_MSR]))
+			goto badframe;
+	}
+
+	if (IS_ENABLED(CONFIG_PPC_TRANSACTIONAL_MEM) && MSR_TM_ACTIVE(msr)) {
 		/* We recheckpoint on return. */
 		struct ucontext __user *uc_transact;
 
@@ -778,9 +784,7 @@ SYSCALL_DEFINE0(rt_sigreturn)
 		if (restore_tm_sigcontexts(current, &uc->uc_mcontext,
 					   &uc_transact->uc_mcontext))
 			goto badframe;
-	} else
-#endif
-	{
+	} else {
 		/*
 		 * Fall through, for non-TM restore
 		 *
@@ -818,10 +822,8 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
 	unsigned long newsp = 0;
 	long err = 0;
 	struct pt_regs *regs = tsk->thread.regs;
-#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 	/* Save the thread's msr before get_tm_stackpointer() changes it */
 	unsigned long msr = regs->msr;
-#endif
 
 	frame = get_sigframe(ksig, tsk, sizeof(*frame), 0);
 	if (!access_ok(frame, sizeof(*frame)))
@@ -836,8 +838,9 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
 	/* Create the ucontext.  */
 	err |= __put_user(0, &frame->uc.uc_flags);
 	err |= __save_altstack(&frame->uc.uc_stack, regs->gpr[1]);
-#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+
 	if (MSR_TM_ACTIVE(msr)) {
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 		/* The ucontext_t passed to userland points to the second
 		 * ucontext_t (for transactional state) with its uc_link ptr.
 		 */
@@ -847,9 +850,8 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
 					    tsk, ksig->sig, NULL,
 					    (unsigned long)ksig->ka.sa.sa_handler,
 					    msr);
-	} else
 #endif
-	{
+	} else {
 		err |= __put_user(0, &frame->uc.uc_link);
 		prepare_setup_sigcontext(tsk);
 		err |= setup_sigcontext(&frame->uc.uc_mcontext, tsk, ksig->sig,
-- 
2.26.1

[PATCH v7 06/10] powerpc/signal64: Replace setup_sigcontext() w/ unsafe_setup_sigcontext()

[Christopher M. Riedl]

Previously setup_sigcontext() performed a costly KUAP switch on every
uaccess operation. These repeated uaccess switches cause a significant
drop in signal handling performance.

Rewrite setup_sigcontext() to assume that a userspace write access window
is open by replacing all uaccess functions with their 'unsafe' versions.
Modify the callers to first open, call unsafe_setup_sigcontext() and
then close the uaccess window.

Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
---
v7:	* Don't use unsafe_op_wrap() since Christophe indicates this
	  macro may go away in the future.
---
 arch/powerpc/kernel/signal_64.c | 72 ++++++++++++++++++++-------------
 1 file changed, 45 insertions(+), 27 deletions(-)

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index bd8d210c9115..78ae4bb4e590 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -101,9 +101,14 @@ static void prepare_setup_sigcontext(struct task_struct *tsk)
  * Set up the sigcontext for the signal frame.
  */
 
-static long setup_sigcontext(struct sigcontext __user *sc,
-		struct task_struct *tsk, int signr, sigset_t *set,
-		unsigned long handler, int ctx_has_vsx_region)
+#define unsafe_setup_sigcontext(sc, tsk, signr, set, handler, ctx_has_vsx_region, label)\
+do {											\
+	if (__unsafe_setup_sigcontext(sc, tsk, signr, set, handler, ctx_has_vsx_region))\
+		goto label;								\
+} while (0)
+static long notrace __unsafe_setup_sigcontext(struct sigcontext __user *sc,
+					struct task_struct *tsk, int signr, sigset_t *set,
+					unsigned long handler, int ctx_has_vsx_region)
 {
 	/* When CONFIG_ALTIVEC is set, we _always_ setup v_regs even if the
 	 * process never used altivec yet (MSR_VEC is zero in pt_regs of
@@ -118,20 +123,19 @@ static long setup_sigcontext(struct sigcontext __user *sc,
 #endif
 	struct pt_regs *regs = tsk->thread.regs;
 	unsigned long msr = regs->msr;
-	long err = 0;
 	/* Force usr to alway see softe as 1 (interrupts enabled) */
 	unsigned long softe = 0x1;
 
 	BUG_ON(tsk != current);
 
 #ifdef CONFIG_ALTIVEC
-	err |= __put_user(v_regs, &sc->v_regs);
+	unsafe_put_user(v_regs, &sc->v_regs, efault_out);
 
 	/* save altivec registers */
 	if (tsk->thread.used_vr) {
 		/* Copy 33 vec registers (vr0..31 and vscr) to the stack */
-		err |= __copy_to_user(v_regs, &tsk->thread.vr_state,
-				      33 * sizeof(vector128));
+		unsafe_copy_to_user(v_regs, &tsk->thread.vr_state,
+				    33 * sizeof(vector128), efault_out);
 		/* set MSR_VEC in the MSR value in the frame to indicate that sc->v_reg)
 		 * contains valid data.
 		 */
@@ -140,12 +144,12 @@ static long setup_sigcontext(struct sigcontext __user *sc,
 	/* We always copy to/from vrsave, it's 0 if we don't have or don't
 	 * use altivec.
 	 */
-	err |= __put_user(tsk->thread.vrsave, (u32 __user *)&v_regs[33]);
+	unsafe_put_user(tsk->thread.vrsave, (u32 __user *)&v_regs[33], efault_out);
 #else /* CONFIG_ALTIVEC */
-	err |= __put_user(0, &sc->v_regs);
+	unsafe_put_user(0, &sc->v_regs, efault_out);
 #endif /* CONFIG_ALTIVEC */
 	/* copy fpr regs and fpscr */
-	err |= copy_fpr_to_user(&sc->fp_regs, tsk);
+	unsafe_copy_fpr_to_user(&sc->fp_regs, tsk, efault_out);
 
 	/*
 	 * Clear the MSR VSX bit to indicate there is no valid state attached
@@ -160,24 +164,27 @@ static long setup_sigcontext(struct sigcontext __user *sc,
 	 */
 	if (tsk->thread.used_vsr && ctx_has_vsx_region) {
 		v_regs += ELF_NVRREG;
-		err |= copy_vsx_to_user(v_regs, tsk);
+		unsafe_copy_vsx_to_user(v_regs, tsk, efault_out);
 		/* set MSR_VSX in the MSR value in the frame to
 		 * indicate that sc->vs_reg) contains valid data.
 		 */
 		msr |= MSR_VSX;
 	}
 #endif /* CONFIG_VSX */
-	err |= __put_user(&sc->gp_regs, &sc->regs);
+	unsafe_put_user(&sc->gp_regs, &sc->regs, efault_out);
 	WARN_ON(!FULL_REGS(regs));
-	err |= __copy_to_user(&sc->gp_regs, regs, GP_REGS_SIZE);
-	err |= __put_user(msr, &sc->gp_regs[PT_MSR]);
-	err |= __put_user(softe, &sc->gp_regs[PT_SOFTE]);
-	err |= __put_user(signr, &sc->signal);
-	err |= __put_user(handler, &sc->handler);
+	unsafe_copy_to_user(&sc->gp_regs, regs, GP_REGS_SIZE, efault_out);
+	unsafe_put_user(msr, &sc->gp_regs[PT_MSR], efault_out);
+	unsafe_put_user(softe, &sc->gp_regs[PT_SOFTE], efault_out);
+	unsafe_put_user(signr, &sc->signal, efault_out);
+	unsafe_put_user(handler, &sc->handler, efault_out);
 	if (set != NULL)
-		err |=  __put_user(set->sig[0], &sc->oldmask);
+		unsafe_put_user(set->sig[0], &sc->oldmask, efault_out);
 
-	return err;
+	return 0;
+
+efault_out:
+	return -EFAULT;
 }
 
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
@@ -670,12 +677,15 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
 
 	if (old_ctx != NULL) {
 		prepare_setup_sigcontext(current);
-		if (!access_ok(old_ctx, ctx_size)
-		    || setup_sigcontext(&old_ctx->uc_mcontext, current, 0, NULL, 0,
-					ctx_has_vsx_region)
-		    || __copy_to_user(&old_ctx->uc_sigmask,
-				      &current->blocked, sizeof(sigset_t)))
+		if (!user_write_access_begin(old_ctx, ctx_size))
 			return -EFAULT;
+
+		unsafe_setup_sigcontext(&old_ctx->uc_mcontext, current, 0, NULL,
+					0, ctx_has_vsx_region, efault_out);
+		unsafe_copy_to_user(&old_ctx->uc_sigmask, &current->blocked,
+				    sizeof(sigset_t), efault_out);
+
+		user_write_access_end();
 	}
 	if (new_ctx == NULL)
 		return 0;
@@ -704,6 +714,10 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
 	/* This returns like rt_sigreturn */
 	set_thread_flag(TIF_RESTOREALL);
 	return 0;
+
+efault_out:
+	user_write_access_end();
+	return -EFAULT;
 }
 
 
@@ -854,9 +868,13 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
 	} else {
 		err |= __put_user(0, &frame->uc.uc_link);
 		prepare_setup_sigcontext(tsk);
-		err |= setup_sigcontext(&frame->uc.uc_mcontext, tsk, ksig->sig,
-					NULL, (unsigned long)ksig->ka.sa.sa_handler,
-					1);
+		if (!user_write_access_begin(&frame->uc.uc_mcontext,
+					     sizeof(frame->uc.uc_mcontext)))
+			return -EFAULT;
+		err |= __unsafe_setup_sigcontext(&frame->uc.uc_mcontext, tsk,
+						ksig->sig, NULL,
+						(unsigned long)ksig->ka.sa.sa_handler, 1);
+		user_write_access_end();
 	}
 	err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
 	if (err)
-- 
2.26.1

[PATCH v7 07/10] powerpc/signal64: Replace restore_sigcontext() w/ unsafe_restore_sigcontext()

[Christopher M. Riedl]

Previously restore_sigcontext() performed a costly KUAP switch on every
uaccess operation. These repeated uaccess switches cause a significant
drop in signal handling performance.

Rewrite restore_sigcontext() to assume that a userspace read access
window is open by replacing all uaccess functions with their 'unsafe'
versions. Modify the callers to first open, call
unsafe_restore_sigcontext(), and then close the uaccess window.

Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
---
v7:	* Don't use unsafe_op_wrap() since Christophe indicates this
	  macro may go away in the future.
---
 arch/powerpc/kernel/signal_64.c | 68 ++++++++++++++++++++-------------
 1 file changed, 41 insertions(+), 27 deletions(-)

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index 78ae4bb4e590..23a44ec3ac01 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -327,14 +327,16 @@ static long setup_tm_sigcontexts(struct sigcontext __user *sc,
 /*
  * Restore the sigcontext from the signal frame.
  */
-
-static long restore_sigcontext(struct task_struct *tsk, sigset_t *set, int sig,
-			      struct sigcontext __user *sc)
+#define unsafe_restore_sigcontext(tsk, set, sig, sc, label) do {	\
+	if (__unsafe_restore_sigcontext(tsk, set, sig, sc))		\
+		goto label;						\
+} while (0)
+static long notrace __unsafe_restore_sigcontext(struct task_struct *tsk, sigset_t *set,
+						int sig, struct sigcontext __user *sc)
 {
 #ifdef CONFIG_ALTIVEC
 	elf_vrreg_t __user *v_regs;
 #endif
-	unsigned long err = 0;
 	unsigned long save_r13 = 0;
 	unsigned long msr;
 	struct pt_regs *regs = tsk->thread.regs;
@@ -349,27 +351,27 @@ static long restore_sigcontext(struct task_struct *tsk, sigset_t *set, int sig,
 		save_r13 = regs->gpr[13];
 
 	/* copy the GPRs */
-	err |= __copy_from_user(regs->gpr, sc->gp_regs, sizeof(regs->gpr));
-	err |= __get_user(regs->nip, &sc->gp_regs[PT_NIP]);
+	unsafe_copy_from_user(regs->gpr, sc->gp_regs, sizeof(regs->gpr), efault_out);
+	unsafe_get_user(regs->nip, &sc->gp_regs[PT_NIP], efault_out);
 	/* get MSR separately, transfer the LE bit if doing signal return */
-	err |= __get_user(msr, &sc->gp_regs[PT_MSR]);
+	unsafe_get_user(msr, &sc->gp_regs[PT_MSR], efault_out);
 	if (sig)
 		regs->msr = (regs->msr & ~MSR_LE) | (msr & MSR_LE);
-	err |= __get_user(regs->orig_gpr3, &sc->gp_regs[PT_ORIG_R3]);
-	err |= __get_user(regs->ctr, &sc->gp_regs[PT_CTR]);
-	err |= __get_user(regs->link, &sc->gp_regs[PT_LNK]);
-	err |= __get_user(regs->xer, &sc->gp_regs[PT_XER]);
-	err |= __get_user(regs->ccr, &sc->gp_regs[PT_CCR]);
+	unsafe_get_user(regs->orig_gpr3, &sc->gp_regs[PT_ORIG_R3], efault_out);
+	unsafe_get_user(regs->ctr, &sc->gp_regs[PT_CTR], efault_out);
+	unsafe_get_user(regs->link, &sc->gp_regs[PT_LNK], efault_out);
+	unsafe_get_user(regs->xer, &sc->gp_regs[PT_XER], efault_out);
+	unsafe_get_user(regs->ccr, &sc->gp_regs[PT_CCR], efault_out);
 	/* Don't allow userspace to set SOFTE */
 	set_trap_norestart(regs);
-	err |= __get_user(regs->dar, &sc->gp_regs[PT_DAR]);
-	err |= __get_user(regs->dsisr, &sc->gp_regs[PT_DSISR]);
-	err |= __get_user(regs->result, &sc->gp_regs[PT_RESULT]);
+	unsafe_get_user(regs->dar, &sc->gp_regs[PT_DAR], efault_out);
+	unsafe_get_user(regs->dsisr, &sc->gp_regs[PT_DSISR], efault_out);
+	unsafe_get_user(regs->result, &sc->gp_regs[PT_RESULT], efault_out);
 
 	if (!sig)
 		regs->gpr[13] = save_r13;
 	if (set != NULL)
-		err |=  __get_user(set->sig[0], &sc->oldmask);
+		unsafe_get_user(set->sig[0], &sc->oldmask, efault_out);
 
 	/*
 	 * Force reload of FP/VEC.
@@ -379,29 +381,27 @@ static long restore_sigcontext(struct task_struct *tsk, sigset_t *set, int sig,
 	regs->msr &= ~(MSR_FP | MSR_FE0 | MSR_FE1 | MSR_VEC | MSR_VSX);
 
 #ifdef CONFIG_ALTIVEC
-	err |= __get_user(v_regs, &sc->v_regs);
-	if (err)
-		return err;
+	unsafe_get_user(v_regs, &sc->v_regs, efault_out);
 	if (v_regs && !access_ok(v_regs, 34 * sizeof(vector128)))
 		return -EFAULT;
 	/* Copy 33 vec registers (vr0..31 and vscr) from the stack */
 	if (v_regs != NULL && (msr & MSR_VEC) != 0) {
-		err |= __copy_from_user(&tsk->thread.vr_state, v_regs,
-					33 * sizeof(vector128));
+		unsafe_copy_from_user(&tsk->thread.vr_state, v_regs,
+				      33 * sizeof(vector128), efault_out);
 		tsk->thread.used_vr = true;
 	} else if (tsk->thread.used_vr) {
 		memset(&tsk->thread.vr_state, 0, 33 * sizeof(vector128));
 	}
 	/* Always get VRSAVE back */
 	if (v_regs != NULL)
-		err |= __get_user(tsk->thread.vrsave, (u32 __user *)&v_regs[33]);
+		unsafe_get_user(tsk->thread.vrsave, (u32 __user *)&v_regs[33], efault_out);
 	else
 		tsk->thread.vrsave = 0;
 	if (cpu_has_feature(CPU_FTR_ALTIVEC))
 		mtspr(SPRN_VRSAVE, tsk->thread.vrsave);
 #endif /* CONFIG_ALTIVEC */
 	/* restore floating point */
-	err |= copy_fpr_from_user(tsk, &sc->fp_regs);
+	unsafe_copy_fpr_from_user(tsk, &sc->fp_regs, efault_out);
 #ifdef CONFIG_VSX
 	/*
 	 * Get additional VSX data. Update v_regs to point after the
@@ -410,14 +410,17 @@ static long restore_sigcontext(struct task_struct *tsk, sigset_t *set, int sig,
 	 */
 	v_regs += ELF_NVRREG;
 	if ((msr & MSR_VSX) != 0) {
-		err |= copy_vsx_from_user(tsk, v_regs);
+		unsafe_copy_vsx_from_user(tsk, v_regs, efault_out);
 		tsk->thread.used_vsr = true;
 	} else {
 		for (i = 0; i < 32 ; i++)
 			tsk->thread.fp_state.fpr[i][TS_VSRLOWOFFSET] = 0;
 	}
 #endif
-	return err;
+	return 0;
+
+efault_out:
+	return -EFAULT;
 }
 
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
@@ -708,8 +711,14 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
 	if (__copy_from_user(&set, &new_ctx->uc_sigmask, sizeof(set)))
 		do_exit(SIGSEGV);
 	set_current_blocked(&set);
-	if (restore_sigcontext(current, NULL, 0, &new_ctx->uc_mcontext))
+
+	if (!user_read_access_begin(new_ctx, ctx_size))
+		return -EFAULT;
+	if (__unsafe_restore_sigcontext(current, NULL, 0, &new_ctx->uc_mcontext)) {
+		user_read_access_end();
 		do_exit(SIGSEGV);
+	}
+	user_read_access_end();
 
 	/* This returns like rt_sigreturn */
 	set_thread_flag(TIF_RESTOREALL);
@@ -812,8 +821,13 @@ SYSCALL_DEFINE0(rt_sigreturn)
 		 * causing a TM bad thing.
 		 */
 		current->thread.regs->msr &= ~MSR_TS_MASK;
-		if (restore_sigcontext(current, NULL, 1, &uc->uc_mcontext))
+		if (!user_read_access_begin(&uc->uc_mcontext, sizeof(uc->uc_mcontext)))
+			return -EFAULT;
+		if (__unsafe_restore_sigcontext(current, NULL, 1, &uc->uc_mcontext)) {
+			user_read_access_end();
 			goto badframe;
+		}
+		user_read_access_end();
 	}
 
 	if (restore_altstack(&uc->uc_stack))
-- 
2.26.1

[PATCH v7 08/10] powerpc/signal64: Rewrite handle_rt_signal64() to minimise uaccess switches

[Christopher M. Riedl]

From: Daniel Axtens <dja@axtens.net>

Add uaccess blocks and use the 'unsafe' versions of functions doing user
access where possible to reduce the number of times uaccess has to be
opened/closed.

There is no 'unsafe' version of copy_siginfo_to_user, so move it
slightly to allow for a "longer" uaccess block.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Co-developed-by: Christopher M. Riedl <cmr@codefail.de>
Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
---
 arch/powerpc/kernel/signal_64.c | 56 ++++++++++++++++++++-------------
 1 file changed, 35 insertions(+), 21 deletions(-)

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index 23a44ec3ac01..788854734b9a 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -854,45 +854,52 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
 	unsigned long msr = regs->msr;
 
 	frame = get_sigframe(ksig, tsk, sizeof(*frame), 0);
-	if (!access_ok(frame, sizeof(*frame)))
-		goto badframe;
 
-	err |= __put_user(&frame->info, &frame->pinfo);
-	err |= __put_user(&frame->uc, &frame->puc);
-	err |= copy_siginfo_to_user(&frame->info, &ksig->info);
-	if (err)
+	/* This only applies when calling unsafe_setup_sigcontext() and must be
+	 * called before opening the uaccess window.
+	 */
+	if (!MSR_TM_ACTIVE(msr))
+		prepare_setup_sigcontext(tsk);
+
+	if (!user_write_access_begin(frame, sizeof(*frame)))
 		goto badframe;
 
+	unsafe_put_user(&frame->info, &frame->pinfo, badframe_block);
+	unsafe_put_user(&frame->uc, &frame->puc, badframe_block);
+
 	/* Create the ucontext.  */
-	err |= __put_user(0, &frame->uc.uc_flags);
-	err |= __save_altstack(&frame->uc.uc_stack, regs->gpr[1]);
+	unsafe_put_user(0, &frame->uc.uc_flags, badframe_block);
+	unsafe_save_altstack(&frame->uc.uc_stack, regs->gpr[1], badframe_block);
 
 	if (MSR_TM_ACTIVE(msr)) {
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 		/* The ucontext_t passed to userland points to the second
 		 * ucontext_t (for transactional state) with its uc_link ptr.
 		 */
-		err |= __put_user(&frame->uc_transact, &frame->uc.uc_link);
+		unsafe_put_user(&frame->uc_transact, &frame->uc.uc_link, badframe_block);
+
+		user_write_access_end();
+
 		err |= setup_tm_sigcontexts(&frame->uc.uc_mcontext,
 					    &frame->uc_transact.uc_mcontext,
 					    tsk, ksig->sig, NULL,
 					    (unsigned long)ksig->ka.sa.sa_handler,
 					    msr);
+
+		if (!user_write_access_begin(&frame->uc.uc_sigmask,
+					     sizeof(frame->uc.uc_sigmask)))
+			goto badframe;
+
 #endif
 	} else {
-		err |= __put_user(0, &frame->uc.uc_link);
-		prepare_setup_sigcontext(tsk);
-		if (!user_write_access_begin(&frame->uc.uc_mcontext,
-					     sizeof(frame->uc.uc_mcontext)))
-			return -EFAULT;
-		err |= __unsafe_setup_sigcontext(&frame->uc.uc_mcontext, tsk,
-						ksig->sig, NULL,
-						(unsigned long)ksig->ka.sa.sa_handler, 1);
-		user_write_access_end();
+		unsafe_put_user(0, &frame->uc.uc_link, badframe_block);
+		unsafe_setup_sigcontext(&frame->uc.uc_mcontext, tsk, ksig->sig,
+					NULL, (unsigned long)ksig->ka.sa.sa_handler,
+					1, badframe_block);
 	}
-	err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
-	if (err)
-		goto badframe;
+
+	unsafe_copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set), badframe_block);
+	user_write_access_end();
 
 	/* Make sure signal handler doesn't get spurious FP exceptions */
 	tsk->thread.fp_state.fpscr = 0;
@@ -907,6 +914,11 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
 		regs->nip = (unsigned long) &frame->tramp[0];
 	}
 
+
+	/* Save the siginfo outside of the unsafe block. */
+	if (copy_siginfo_to_user(&frame->info, &ksig->info))
+		goto badframe;
+
 	/* Allocate a dummy caller frame for the signal handler. */
 	newsp = ((unsigned long)frame) - __SIGNAL_FRAMESIZE;
 	err |= put_user(regs->gpr[1], (unsigned long __user *)newsp);
@@ -946,6 +958,8 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
 
 	return 0;
 
+badframe_block:
+	user_write_access_end();
 badframe:
 	signal_fault(current, regs, "handle_rt_signal64", frame);
 
-- 
2.26.1

[PATCH v7 09/10] powerpc/signal64: Rewrite rt_sigreturn() to minimise uaccess switches

[Christopher M. Riedl]

From: Daniel Axtens <dja@axtens.net>

Add uaccess blocks and use the 'unsafe' versions of functions doing user
access where possible to reduce the number of times uaccess has to be
opened/closed.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Co-developed-by: Christopher M. Riedl <cmr@codefail.de>
Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
---
 arch/powerpc/kernel/signal_64.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index 788854734b9a..00c907022707 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -822,11 +822,11 @@ SYSCALL_DEFINE0(rt_sigreturn)
 		 */
 		current->thread.regs->msr &= ~MSR_TS_MASK;
 		if (!user_read_access_begin(&uc->uc_mcontext, sizeof(uc->uc_mcontext)))
-			return -EFAULT;
-		if (__unsafe_restore_sigcontext(current, NULL, 1, &uc->uc_mcontext)) {
-			user_read_access_end();
 			goto badframe;
-		}
+
+		unsafe_restore_sigcontext(current, NULL, 1, &uc->uc_mcontext,
+					  badframe_block);
+
 		user_read_access_end();
 	}
 
@@ -836,6 +836,8 @@ SYSCALL_DEFINE0(rt_sigreturn)
 	set_thread_flag(TIF_RESTOREALL);
 	return 0;
 
+badframe_block:
+	user_read_access_end();
 badframe:
 	signal_fault(current, regs, "rt_sigreturn", uc);
 
-- 
2.26.1

[PATCH v7 10/10] powerpc/signal: Use __get_user() to copy sigset_t

[Christopher M. Riedl]

Usually sigset_t is exactly 8B which is a "trivial" size and does not
warrant using __copy_from_user(). Use __get_user() directly in
anticipation of future work to remove the trivial size optimizations
from __copy_from_user().

The ppc32 implementation of get_sigset_t() previously called
copy_from_user() which, unlike __copy_from_user(), calls access_ok().
Replacing this w/ __get_user() (no access_ok()) is fine here since both
callsites in signal_32.c are preceded by an earlier access_ok().

Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
---
 arch/powerpc/kernel/signal.h    | 7 +++++++
 arch/powerpc/kernel/signal_32.c | 2 +-
 arch/powerpc/kernel/signal_64.c | 4 ++--
 3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/signal.h b/arch/powerpc/kernel/signal.h
index d8dd76b1dc94..1393876f3814 100644
--- a/arch/powerpc/kernel/signal.h
+++ b/arch/powerpc/kernel/signal.h
@@ -19,6 +19,13 @@ extern int handle_signal32(struct ksignal *ksig, sigset_t *oldset,
 extern int handle_rt_signal32(struct ksignal *ksig, sigset_t *oldset,
 			      struct task_struct *tsk);
 
+static inline int __get_user_sigset(sigset_t *dst, const sigset_t __user *src)
+{
+	BUILD_BUG_ON(sizeof(sigset_t) != sizeof(u64));
+
+	return __get_user(dst->sig[0], (u64 __user *)&src->sig[0]);
+}
+
 #ifdef CONFIG_VSX
 extern unsigned long copy_vsx_to_user(void __user *to,
 				      struct task_struct *task);
diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
index 75ee918a120a..c505b444a613 100644
--- a/arch/powerpc/kernel/signal_32.c
+++ b/arch/powerpc/kernel/signal_32.c
@@ -144,7 +144,7 @@ static inline int restore_general_regs(struct pt_regs *regs,
 
 static inline int get_sigset_t(sigset_t *set, const sigset_t __user *uset)
 {
-	return copy_from_user(set, uset, sizeof(*uset));
+	return __get_user_sigset(set, uset);
 }
 
 #define to_user_ptr(p)		((unsigned long)(p))
diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index 00c907022707..debe88055f38 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -708,7 +708,7 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx,
 	 * We kill the task with a SIGSEGV in this situation.
 	 */
 
-	if (__copy_from_user(&set, &new_ctx->uc_sigmask, sizeof(set)))
+	if (__get_user_sigset(&set, &new_ctx->uc_sigmask))
 		do_exit(SIGSEGV);
 	set_current_blocked(&set);
 
@@ -747,7 +747,7 @@ SYSCALL_DEFINE0(rt_sigreturn)
 	if (!access_ok(uc, sizeof(*uc)))
 		goto badframe;
 
-	if (__copy_from_user(&set, &uc->uc_sigmask, sizeof(set)))
+	if (__get_user_sigset(&set, &uc->uc_sigmask))
 		goto badframe;
 	set_current_blocked(&set);
 
-- 
2.26.1

Re: [PATCH v7 00/10] Improve signal performance on PPC64 with KUAP

[Michael Ellerman]

On Fri, 26 Feb 2021 19:12:49 -0600, Christopher M. Riedl wrote:
> As reported by Anton, there is a large penalty to signal handling
> performance on radix systems using KUAP. The signal handling code
> performs many user access operations, each of which needs to switch the
> KUAP permissions bit to open and then close user access. This involves a
> costly 'mtspr' operation [0].
> 
> There is existing work done on x86 and by Christophe Leroy for PPC32 to
> instead open up user access in "blocks" using user_*_access_{begin,end}.
> We can do the same in PPC64 to bring performance back up on KUAP-enabled
> radix and now also hash MMU systems [1].
> 
> [...]

Applied to powerpc/next.

[01/10] powerpc/uaccess: Add unsafe_copy_from_user()
        https://git.kernel.org/powerpc/c/9466c1799fa2acb68e505a264dcdf53779101ac6
[02/10] powerpc/signal: Add unsafe_copy_{vsx, fpr}_from_user()
        https://git.kernel.org/powerpc/c/609355dfc88e2921bfcbd879300d482a9a33378e
[03/10] powerpc/signal64: Remove non-inline calls from setup_sigcontext()
        https://git.kernel.org/powerpc/c/c6c9645e37483444ec5182373455b2f22e4b1535
[04/10] powerpc: Reference parameter in MSR_TM_ACTIVE() macro
        https://git.kernel.org/powerpc/c/1a130b67c682be9842f188f593c2080786de4204
[05/10] powerpc/signal64: Remove TM ifdefery in middle of if/else block
        https://git.kernel.org/powerpc/c/2d19630e20fe5fbd5813f73fd5b1c81ddec61369
[06/10] powerpc/signal64: Replace setup_sigcontext() w/ unsafe_setup_sigcontext()
        https://git.kernel.org/powerpc/c/7bb081c8f043ab166f8c6f26fca744821217dad7
[07/10] powerpc/signal64: Replace restore_sigcontext() w/ unsafe_restore_sigcontext()
        https://git.kernel.org/powerpc/c/193323e1009437c0885240e75ca71f7963e4a006
[08/10] powerpc/signal64: Rewrite handle_rt_signal64() to minimise uaccess switches
        https://git.kernel.org/powerpc/c/96d7a4e06fab9fbc4f67c563af65b073902f3e61
[09/10] powerpc/signal64: Rewrite rt_sigreturn() to minimise uaccess switches
        https://git.kernel.org/powerpc/c/0f92433b8f9f76608528101e7a81cd3bfd00e236
[10/10] powerpc/signal: Use __get_user() to copy sigset_t
        https://git.kernel.org/powerpc/c/d3ccc9781560af051554017c702631560bdc0811

cheers