[PATCH AUTOSEL 5.8 62/63] arm64: Move handling of erratum 1418040 into C code

From: Sasha Levin
Date: Mon Aug 24 2020 - 13:16:06 EST


From: Marc Zyngier <maz@xxxxxxxxxx>

[ Upstream commit d49f7d7376d0c0daf8680984a37bd07581ac7d38 ]

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

Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
Tested-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>
Reviewed-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>
Acked-by: Will Deacon <will@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20200731173824.107480-2-maz@xxxxxxxxxx
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
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 35de8ba60e3d5..44445d471442d 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 6089638c7d43f..d8a10cf28f827 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
--
2.25.1