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* [PATCH v3 0/4] arm64/sme: SME related fixes
@ 2022-08-17 18:23 Mark Brown
  2022-08-17 18:23 ` [PATCH v3 1/4] arm64/signal: Raise limit on stack frames Mark Brown
                   ` (4 more replies)
  0 siblings, 5 replies; 6+ messages in thread
From: Mark Brown @ 2022-08-17 18:23 UTC (permalink / raw)
  To: Catalin Marinas, Will Deacon; +Cc: linux-arm-kernel, Mark Brown

This series collates together a number of SME related fixes that have
come up in testing.

v3:
 - Use SZ_256K to define the signal frame size limit.
v2:
 - Rebase onto v6.0-rc1.
 - Fix allnoconfig build.

Mark Brown (4):
  arm64/signal: Raise limit on stack frames
  arm64/signal: Flush FPSIMD register state when disabling streaming
    mode
  arm64/sme: Don't flush SVE register state when allocating SME storage
  arm64/sme: Don't flush SVE register state when handling SME traps

 arch/arm64/include/asm/fpsimd.h |  4 ++--
 arch/arm64/kernel/fpsimd.c      | 21 ++++++---------------
 arch/arm64/kernel/ptrace.c      |  6 +++---
 arch/arm64/kernel/signal.c      | 14 ++++++++++++--
 4 files changed, 23 insertions(+), 22 deletions(-)


base-commit: 568035b01cfb107af8d2e4bd2fb9aea22cf5b868
-- 
2.30.2


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^ permalink raw reply	[flat|nested] 6+ messages in thread
* [PATCH v3 1/4] arm64/signal: Raise limit on stack frames
  2022-08-17 18:23 [PATCH v3 0/4] arm64/sme: SME related fixes Mark Brown
@ 2022-08-17 18:23 ` Mark Brown
  2022-08-17 18:23 ` [PATCH v3 2/4] arm64/signal: Flush FPSIMD register state when disabling streaming mode Mark Brown
                   ` (3 subsequent siblings)
  4 siblings, 0 replies; 6+ messages in thread
From: Mark Brown @ 2022-08-17 18:23 UTC (permalink / raw)
  To: Catalin Marinas, Will Deacon; +Cc: linux-arm-kernel, Mark Brown

The signal code has a limit of 64K on the size of a stack frame that it
will generate, if this limit is exceeded then a process will be killed if
it receives a signal. Unfortunately with the advent of SME this limit is
too small - the maximum possible size of the ZA register alone is 64K. This
is not an issue for practical systems at present but is easily seen using
virtual platforms.

Raise the limit to 256K, this is substantially more than could be used by
any current architecture extension.

Signed-off-by: Mark Brown <broonie@kernel.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
---
 arch/arm64/kernel/signal.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index 3e6d0352d7d3..0685b8784927 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -91,7 +91,7 @@ static size_t sigframe_size(struct rt_sigframe_user_layout const *user)
  * not taken into account.  This limit is not a guarantee and is
  * NOT ABI.
  */
-#define SIGFRAME_MAXSZ SZ_64K
+#define SIGFRAME_MAXSZ SZ_256K
 
 static int __sigframe_alloc(struct rt_sigframe_user_layout *user,
 			    unsigned long *offset, size_t size, bool extend)
-- 
2.30.2


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^ permalink raw reply related	[flat|nested] 6+ messages in thread
* [PATCH v3 2/4] arm64/signal: Flush FPSIMD register state when disabling streaming mode
  2022-08-17 18:23 [PATCH v3 0/4] arm64/sme: SME related fixes Mark Brown
  2022-08-17 18:23 ` [PATCH v3 1/4] arm64/signal: Raise limit on stack frames Mark Brown
@ 2022-08-17 18:23 ` Mark Brown
  2022-08-17 18:23 ` [PATCH v3 3/4] arm64/sme: Don't flush SVE register state when allocating SME storage Mark Brown
                   ` (2 subsequent siblings)
  4 siblings, 0 replies; 6+ messages in thread
From: Mark Brown @ 2022-08-17 18:23 UTC (permalink / raw)
  To: Catalin Marinas, Will Deacon; +Cc: linux-arm-kernel, Mark Brown

When handling a signal delivered to a context with streaming mode enabled
we will disable streaming mode for the signal handler, when doing so we
should also flush the saved FPSIMD register state like exiting streaming
mode in the hardware would do so that if that state is reloaded we get the
same behaviour. Without this we will reload whatever the last FPSIMD state
that was saved for the task was.

Fixes: 40a8e87bb3285 ("arm64/sme: Disable ZA and streaming mode when handling signals")
Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
---
 arch/arm64/kernel/signal.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index 0685b8784927..0d28a783a69a 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -926,6 +926,16 @@ static void setup_return(struct pt_regs *regs, struct k_sigaction *ka,
 
 	/* Signal handlers are invoked with ZA and streaming mode disabled */
 	if (system_supports_sme()) {
+		/*
+		 * If we were in streaming mode the saved register
+		 * state was SVE but we will exit SM and use the
+		 * FPSIMD register state - flush the saved FPSIMD
+		 * register state in case it gets loaded.
+		 */
+		if (current->thread.svcr & SVCR_SM_MASK)
+			memset(&current->thread.uw.fpsimd_state, 0,
+			       sizeof(current->thread.uw.fpsimd_state));
+
 		current->thread.svcr &= ~(SVCR_ZA_MASK |
 					  SVCR_SM_MASK);
 		sme_smstop();
-- 
2.30.2


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^ permalink raw reply related	[flat|nested] 6+ messages in thread
* [PATCH v3 3/4] arm64/sme: Don't flush SVE register state when allocating SME storage
  2022-08-17 18:23 [PATCH v3 0/4] arm64/sme: SME related fixes Mark Brown
  2022-08-17 18:23 ` [PATCH v3 1/4] arm64/signal: Raise limit on stack frames Mark Brown
  2022-08-17 18:23 ` [PATCH v3 2/4] arm64/signal: Flush FPSIMD register state when disabling streaming mode Mark Brown
@ 2022-08-17 18:23 ` Mark Brown
  2022-08-17 18:23 ` [PATCH v3 4/4] arm64/sme: Don't flush SVE register state when handling SME traps Mark Brown
  2022-08-23 11:34 ` [PATCH v3 0/4] arm64/sme: SME related fixes Will Deacon
  4 siblings, 0 replies; 6+ messages in thread
From: Mark Brown @ 2022-08-17 18:23 UTC (permalink / raw)
  To: Catalin Marinas, Will Deacon; +Cc: linux-arm-kernel, Mark Brown

Currently when taking a SME access trap we allocate storage for the SVE
register state in order to be able to handle storage of streaming mode SVE.
Due to the original usage in a purely SVE context the SVE register state
allocation this also flushes the register state for SVE if storage was
already allocated but in the SME context this is not desirable. For a SME
access trap to be taken the task must not be in streaming mode so either
there already is SVE register state present for regular SVE mode which would
be corrupted or the task does not have TIF_SVE and the flush is redundant.

Fix this by adding a flag to sve_alloc() indicating if we are in a SVE
context and need to flush the state. Freshly allocated storage is always
zeroed either way.

Fixes: 8bd7f91c03d88 ("arm64/sme: Implement traps and syscall handling for SME")
Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
---
 arch/arm64/include/asm/fpsimd.h |  4 ++--
 arch/arm64/kernel/fpsimd.c      | 10 ++++++----
 arch/arm64/kernel/ptrace.c      |  6 +++---
 arch/arm64/kernel/signal.c      |  2 +-
 4 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/include/asm/fpsimd.h b/arch/arm64/include/asm/fpsimd.h
index 9bb1873f5295..6f86b7ab6c28 100644
--- a/arch/arm64/include/asm/fpsimd.h
+++ b/arch/arm64/include/asm/fpsimd.h
@@ -153,7 +153,7 @@ struct vl_info {
 
 #ifdef CONFIG_ARM64_SVE
 
-extern void sve_alloc(struct task_struct *task);
+extern void sve_alloc(struct task_struct *task, bool flush);
 extern void fpsimd_release_task(struct task_struct *task);
 extern void fpsimd_sync_to_sve(struct task_struct *task);
 extern void fpsimd_force_sync_to_sve(struct task_struct *task);
@@ -256,7 +256,7 @@ size_t sve_state_size(struct task_struct const *task);
 
 #else /* ! CONFIG_ARM64_SVE */
 
-static inline void sve_alloc(struct task_struct *task) { }
+static inline void sve_alloc(struct task_struct *task, bool flush) { }
 static inline void fpsimd_release_task(struct task_struct *task) { }
 static inline void sve_sync_to_fpsimd(struct task_struct *task) { }
 static inline void sve_sync_from_fpsimd_zeropad(struct task_struct *task) { }
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index dd63ffc3a2fa..b9ae9827e6e8 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -715,10 +715,12 @@ size_t sve_state_size(struct task_struct const *task)
  * do_sve_acc() case, there is no ABI requirement to hide stale data
  * written previously be task.
  */
-void sve_alloc(struct task_struct *task)
+void sve_alloc(struct task_struct *task, bool flush)
 {
 	if (task->thread.sve_state) {
-		memset(task->thread.sve_state, 0, sve_state_size(task));
+		if (flush)
+			memset(task->thread.sve_state, 0,
+			       sve_state_size(task));
 		return;
 	}
 
@@ -1388,7 +1390,7 @@ void do_sve_acc(unsigned long esr, struct pt_regs *regs)
 		return;
 	}
 
-	sve_alloc(current);
+	sve_alloc(current, true);
 	if (!current->thread.sve_state) {
 		force_sig(SIGKILL);
 		return;
@@ -1439,7 +1441,7 @@ void do_sme_acc(unsigned long esr, struct pt_regs *regs)
 		return;
 	}
 
-	sve_alloc(current);
+	sve_alloc(current, false);
 	sme_alloc(current);
 	if (!current->thread.sve_state || !current->thread.za_state) {
 		force_sig(SIGKILL);
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 21da83187a60..eb7c08dfb834 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -882,7 +882,7 @@ static int sve_set_common(struct task_struct *target,
 		 * state and ensure there's storage.
 		 */
 		if (target->thread.svcr != old_svcr)
-			sve_alloc(target);
+			sve_alloc(target, true);
 	}
 
 	/* Registers: FPSIMD-only case */
@@ -912,7 +912,7 @@ static int sve_set_common(struct task_struct *target,
 		goto out;
 	}
 
-	sve_alloc(target);
+	sve_alloc(target, true);
 	if (!target->thread.sve_state) {
 		ret = -ENOMEM;
 		clear_tsk_thread_flag(target, TIF_SVE);
@@ -1082,7 +1082,7 @@ static int za_set(struct task_struct *target,
 
 	/* Ensure there is some SVE storage for streaming mode */
 	if (!target->thread.sve_state) {
-		sve_alloc(target);
+		sve_alloc(target, false);
 		if (!target->thread.sve_state) {
 			clear_thread_flag(TIF_SME);
 			ret = -ENOMEM;
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index 0d28a783a69a..9ad911f1647c 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -310,7 +310,7 @@ static int restore_sve_fpsimd_context(struct user_ctxs *user)
 	fpsimd_flush_task_state(current);
 	/* From now, fpsimd_thread_switch() won't touch thread.sve_state */
 
-	sve_alloc(current);
+	sve_alloc(current, true);
 	if (!current->thread.sve_state) {
 		clear_thread_flag(TIF_SVE);
 		return -ENOMEM;
-- 
2.30.2


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^ permalink raw reply related	[flat|nested] 6+ messages in thread
* [PATCH v3 4/4] arm64/sme: Don't flush SVE register state when handling SME traps
  2022-08-17 18:23 [PATCH v3 0/4] arm64/sme: SME related fixes Mark Brown
                   ` (2 preceding siblings ...)
  2022-08-17 18:23 ` [PATCH v3 3/4] arm64/sme: Don't flush SVE register state when allocating SME storage Mark Brown
@ 2022-08-17 18:23 ` Mark Brown
  2022-08-23 11:34 ` [PATCH v3 0/4] arm64/sme: SME related fixes Will Deacon
  4 siblings, 0 replies; 6+ messages in thread
From: Mark Brown @ 2022-08-17 18:23 UTC (permalink / raw)
  To: Catalin Marinas, Will Deacon; +Cc: linux-arm-kernel, Mark Brown

Currently as part of handling a SME access trap we flush the SVE register
state. This is not needed and would corrupt register state if the task has
access to the SVE registers already. For non-streaming mode accesses the
required flushing will be done in the SVE access trap. For streaming
mode SVE register accesses the architecture guarantees that the register
state will be flushed when streaming mode is entered or exited so there is
no need for us to do so. Simply remove the register initialisation.

Fixes: 8bd7f91c03d88 ("arm64/sme: Implement traps and syscall handling for SME")
Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
---
 arch/arm64/kernel/fpsimd.c | 11 -----------
 1 file changed, 11 deletions(-)

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index b9ae9827e6e8..23834d96d1e7 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -1462,17 +1462,6 @@ void do_sme_acc(unsigned long esr, struct pt_regs *regs)
 		fpsimd_bind_task_to_cpu();
 	}
 
-	/*
-	 * If SVE was not already active initialise the SVE registers,
-	 * any non-shared state between the streaming and regular SVE
-	 * registers is architecturally guaranteed to be zeroed when
-	 * we enter streaming mode.  We do not need to initialize ZA
-	 * since ZA must be disabled at this point and enabling ZA is
-	 * architecturally defined to zero ZA.
-	 */
-	if (system_supports_sve() && !test_thread_flag(TIF_SVE))
-		sve_init_regs();
-
 	put_cpu_fpsimd_context();
 }
 
-- 
2.30.2


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^ permalink raw reply related	[flat|nested] 6+ messages in thread
* Re: [PATCH v3 0/4] arm64/sme: SME related fixes
  2022-08-17 18:23 [PATCH v3 0/4] arm64/sme: SME related fixes Mark Brown
                   ` (3 preceding siblings ...)
  2022-08-17 18:23 ` [PATCH v3 4/4] arm64/sme: Don't flush SVE register state when handling SME traps Mark Brown
@ 2022-08-23 11:34 ` Will Deacon
  4 siblings, 0 replies; 6+ messages in thread
From: Will Deacon @ 2022-08-23 11:34 UTC (permalink / raw)
  To: Catalin Marinas, Mark Brown; +Cc: kernel-team, Will Deacon, linux-arm-kernel

On Wed, 17 Aug 2022 19:23:20 +0100, Mark Brown wrote:
> This series collates together a number of SME related fixes that have
> come up in testing.
> 
> v3:
>  - Use SZ_256K to define the signal frame size limit.
> v2:
>  - Rebase onto v6.0-rc1.
>  - Fix allnoconfig build.
> 
> [...]

Applied to arm64 (for-next/fixes), thanks!

[1/4] arm64/signal: Raise limit on stack frames
      https://git.kernel.org/arm64/c/7ddcaf78e93c
[2/4] arm64/signal: Flush FPSIMD register state when disabling streaming mode
      https://git.kernel.org/arm64/c/ea64baacbc36
[3/4] arm64/sme: Don't flush SVE register state when allocating SME storage
      https://git.kernel.org/arm64/c/826a4fdd2ada
[4/4] arm64/sme: Don't flush SVE register state when handling SME traps
      https://git.kernel.org/arm64/c/714f3cbd70a4

Cheers,
-- 
Will

https://fixes.arm64.dev
https://next.arm64.dev
https://will.arm64.dev

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^ permalink raw reply	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2022-08-23 11:36 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-08-17 18:23 [PATCH v3 0/4] arm64/sme: SME related fixes Mark Brown
2022-08-17 18:23 ` [PATCH v3 1/4] arm64/signal: Raise limit on stack frames Mark Brown
2022-08-17 18:23 ` [PATCH v3 2/4] arm64/signal: Flush FPSIMD register state when disabling streaming mode Mark Brown
2022-08-17 18:23 ` [PATCH v3 3/4] arm64/sme: Don't flush SVE register state when allocating SME storage Mark Brown
2022-08-17 18:23 ` [PATCH v3 4/4] arm64/sme: Don't flush SVE register state when handling SME traps Mark Brown
2022-08-23 11:34 ` [PATCH v3 0/4] arm64/sme: SME related fixes Will Deacon

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