[PATCH 5.4 147/214] arm64: Move handling of erratum 1418040 into C code

Greg Kroah-Hartman
2020-09-01T15:32:55Z

From: Marc Zyngier <maz@kernel.org>

[ 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@kernel.org>
Tested-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20200731173824.107480-2-maz@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/arm64/kernel/process.c | 34 ++++++++++++++++++++++++++++++++++
1 file changed, 34 insertions(+)

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index fab013c5ee8c9..10190c4b16dc4 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -498,6 +498,39 @@ 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.
*/
@@ -514,6 +547,7 @@ __notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev,
uao_thread_switch(next);
ptrauth_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