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* [PATCH v3 0/2] arm64: Allow erratum 1418040 for late CPUs
@ 2020-07-31 17:38 Marc Zyngier
  2020-07-31 17:38 ` [PATCH v3 1/2] arm64: Move handling of erratum 1418040 into C code Marc Zyngier
  2020-07-31 17:38 ` [PATCH v3 2/2] arm64: Allow booting of late CPUs affected by erratum 1418040 Marc Zyngier
  0 siblings, 2 replies; 4+ messages in thread
From: Marc Zyngier @ 2020-07-31 17:38 UTC (permalink / raw)
  To: linux-arm-kernel
  Cc: Sai Prakash Ranjan, kernel-team, Suzuki K Poulose,
	Catalin Marinas, Stephen Boyd, dianders, Will Deacon

Erratum 1418040 currently prevents a late CPU from booting if none
of the early CPUs are affected by it. This is because the handling
is implemented as alternatives, and we have already got rid of them
by the time userspace onlines a new CPU.

A solution to this is to move everything into C code, and rely on
static keys instead. Once this is done, the feature can be allowed
for late CPUs.

Note that CPUs affected by 1418040 also tend to miss AArch32-EL1,
meaning they cannot be used as late CPUs when KVM is enabled and
that their sibblings have AArch32-EL1.

* From v1:
  - Dropped check for kernel threads
  - Added comment describing the switching logic
  - Made the errata handling function __always_inline

* From v2:
  - Dropped __always_inline again
  - Simplified logic

Marc Zyngier (2):
  arm64: Move handling of erratum 1418040 into C code
  arm64: Allow booting of late CPUs affected by erratum 1418040

 arch/arm64/kernel/cpu_errata.c |  2 ++
 arch/arm64/kernel/entry.S      | 21 --------------------
 arch/arm64/kernel/process.c    | 35 ++++++++++++++++++++++++++++++++++
 3 files changed, 37 insertions(+), 21 deletions(-)

-- 
2.27.0

*** BLURB HERE ***

Marc Zyngier (2):
  arm64: Move handling of erratum 1418040 into C code
  arm64: Allow booting of late CPUs affected by erratum 1418040

 arch/arm64/kernel/cpu_errata.c |  2 ++
 arch/arm64/kernel/entry.S      | 21 ---------------------
 arch/arm64/kernel/process.c    | 34 ++++++++++++++++++++++++++++++++++
 3 files changed, 36 insertions(+), 21 deletions(-)

-- 
2.27.0


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^ permalink raw reply	[flat|nested] 4+ messages in thread

* [PATCH v3 1/2] arm64: Move handling of erratum 1418040 into C code
  2020-07-31 17:38 [PATCH v3 0/2] arm64: Allow erratum 1418040 for late CPUs Marc Zyngier
@ 2020-07-31 17:38 ` Marc Zyngier
  2020-07-31 18:00   ` Stephen Boyd
  2020-07-31 17:38 ` [PATCH v3 2/2] arm64: Allow booting of late CPUs affected by erratum 1418040 Marc Zyngier
  1 sibling, 1 reply; 4+ messages in thread
From: Marc Zyngier @ 2020-07-31 17:38 UTC (permalink / raw)
  To: linux-arm-kernel
  Cc: Sai Prakash Ranjan, kernel-team, Suzuki K Poulose,
	Catalin Marinas, Stephen Boyd, dianders, Will Deacon

Instead of dealing with erratum 1418040 on each entry and exit,
let's move the handling to __switch_to() instead, which has
several advantages:

- It can be applied when it matters (switching between 32 and 64
  bit tasks).
- It is written in C (yay!)
- It can rely on static keys rather than alternatives

Tested-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/kernel/entry.S   | 21 ---------------------
 arch/arm64/kernel/process.c | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 21 deletions(-)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 35de8ba60e3d..44445d471442 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -169,19 +169,6 @@ alternative_cb_end
 	stp	x28, x29, [sp, #16 * 14]
 
 	.if	\el == 0
-	.if	\regsize == 32
-	/*
-	 * If we're returning from a 32-bit task on a system affected by
-	 * 1418040 then re-enable userspace access to the virtual counter.
-	 */
-#ifdef CONFIG_ARM64_ERRATUM_1418040
-alternative_if ARM64_WORKAROUND_1418040
-	mrs	x0, cntkctl_el1
-	orr	x0, x0, #2	// ARCH_TIMER_USR_VCT_ACCESS_EN
-	msr	cntkctl_el1, x0
-alternative_else_nop_endif
-#endif
-	.endif
 	clear_gp_regs
 	mrs	x21, sp_el0
 	ldr_this_cpu	tsk, __entry_task, x20
@@ -337,14 +324,6 @@ alternative_else_nop_endif
 	tst	x22, #PSR_MODE32_BIT		// native task?
 	b.eq	3f
 
-#ifdef CONFIG_ARM64_ERRATUM_1418040
-alternative_if ARM64_WORKAROUND_1418040
-	mrs	x0, cntkctl_el1
-	bic	x0, x0, #2			// ARCH_TIMER_USR_VCT_ACCESS_EN
-	msr	cntkctl_el1, x0
-alternative_else_nop_endif
-#endif
-
 #ifdef CONFIG_ARM64_ERRATUM_845719
 alternative_if ARM64_WORKAROUND_845719
 #ifdef CONFIG_PID_IN_CONTEXTIDR
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 6089638c7d43..d8a10cf28f82 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -515,6 +515,39 @@ static void entry_task_switch(struct task_struct *next)
 	__this_cpu_write(__entry_task, next);
 }
 
+/*
+ * ARM erratum 1418040 handling, affecting the 32bit view of CNTVCT.
+ * Assuming the virtual counter is enabled at the beginning of times:
+ *
+ * - disable access when switching from a 64bit task to a 32bit task
+ * - enable access when switching from a 32bit task to a 64bit task
+ */
+static void erratum_1418040_thread_switch(struct task_struct *prev,
+					  struct task_struct *next)
+{
+	bool prev32, next32;
+	u64 val;
+
+	if (!(IS_ENABLED(CONFIG_ARM64_ERRATUM_1418040) &&
+	      cpus_have_const_cap(ARM64_WORKAROUND_1418040)))
+		return;
+
+	prev32 = is_compat_thread(task_thread_info(prev));
+	next32 = is_compat_thread(task_thread_info(next));
+
+	if (prev32 == next32)
+		return;
+
+	val = read_sysreg(cntkctl_el1);
+
+	if (!next32)
+		val |= ARCH_TIMER_USR_VCT_ACCESS_EN;
+	else
+		val &= ~ARCH_TIMER_USR_VCT_ACCESS_EN;
+
+	write_sysreg(val, cntkctl_el1);
+}
+
 /*
  * Thread switching.
  */
@@ -530,6 +563,7 @@ __notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev,
 	entry_task_switch(next);
 	uao_thread_switch(next);
 	ssbs_thread_switch(next);
+	erratum_1418040_thread_switch(prev, next);
 
 	/*
 	 * Complete any pending TLB or cache maintenance on this CPU in case
-- 
2.27.0


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^ permalink raw reply	[flat|nested] 4+ messages in thread

* [PATCH v3 2/2] arm64: Allow booting of late CPUs affected by erratum 1418040
  2020-07-31 17:38 [PATCH v3 0/2] arm64: Allow erratum 1418040 for late CPUs Marc Zyngier
  2020-07-31 17:38 ` [PATCH v3 1/2] arm64: Move handling of erratum 1418040 into C code Marc Zyngier
@ 2020-07-31 17:38 ` Marc Zyngier
  1 sibling, 0 replies; 4+ messages in thread
From: Marc Zyngier @ 2020-07-31 17:38 UTC (permalink / raw)
  To: linux-arm-kernel
  Cc: Sai Prakash Ranjan, kernel-team, Suzuki K Poulose,
	Catalin Marinas, Stephen Boyd, dianders, Will Deacon

As we can now switch from a system that isn't affected by 1418040
to a system that globally is affected, let's allow affected CPUs
to come in at a later time.

Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Acked-by: Will Deacon <will@kernel.org>
Tested-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/kernel/cpu_errata.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 79728bfb5351..2c0b82db825b 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -910,6 +910,8 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
 		.desc = "ARM erratum 1418040",
 		.capability = ARM64_WORKAROUND_1418040,
 		ERRATA_MIDR_RANGE_LIST(erratum_1418040_list),
+		.type = (ARM64_CPUCAP_SCOPE_LOCAL_CPU |
+			 ARM64_CPUCAP_PERMITTED_FOR_LATE_CPU),
 	},
 #endif
 #ifdef CONFIG_ARM64_WORKAROUND_SPECULATIVE_AT
-- 
2.27.0


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http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH v3 1/2] arm64: Move handling of erratum 1418040 into C code
  2020-07-31 17:38 ` [PATCH v3 1/2] arm64: Move handling of erratum 1418040 into C code Marc Zyngier
@ 2020-07-31 18:00   ` Stephen Boyd
  0 siblings, 0 replies; 4+ messages in thread
From: Stephen Boyd @ 2020-07-31 18:00 UTC (permalink / raw)
  To: Marc Zyngier, linux-arm-kernel
  Cc: Sai Prakash Ranjan, Will Deacon, Suzuki K Poulose,
	Catalin Marinas, dianders, kernel-team

Quoting Marc Zyngier (2020-07-31 10:38:23)
> Instead of dealing with erratum 1418040 on each entry and exit,
> let's move the handling to __switch_to() instead, which has
> several advantages:
> 
> - It can be applied when it matters (switching between 32 and 64
>   bit tasks).
> - It is written in C (yay!)
> - It can rely on static keys rather than alternatives
> 
> Tested-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
> Acked-by: Will Deacon <will@kernel.org>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---

Reviewed-by: Stephen Boyd <swboyd@chromium.org>

_______________________________________________
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linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

^ permalink raw reply	[flat|nested] 4+ messages in thread

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Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-07-31 17:38 [PATCH v3 0/2] arm64: Allow erratum 1418040 for late CPUs Marc Zyngier
2020-07-31 17:38 ` [PATCH v3 1/2] arm64: Move handling of erratum 1418040 into C code Marc Zyngier
2020-07-31 18:00   ` Stephen Boyd
2020-07-31 17:38 ` [PATCH v3 2/2] arm64: Allow booting of late CPUs affected by erratum 1418040 Marc Zyngier

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