Re: [PATCH v2 1/2] arm64: Move handling of erratum 1418040 into C code
From: Will Deacon <will@kernel.org>
Date: 2020-07-31 10:43:17
On Fri, Jul 31, 2020 at 09:33:57AM +0100, Marc Zyngier wrote:
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 <redacted> Signed-off-by: Marc Zyngier <maz@kernel.org> --- arch/arm64/kernel/entry.S | 21 --------------------- arch/arm64/kernel/process.c | 35 +++++++++++++++++++++++++++++++++++ 2 files changed, 35 insertions(+), 21 deletions(-)
[...]
quoted hunk ↗ jump to hunk
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index 6089638c7d43..8bbf066224ab 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c@@ -515,6 +515,40 @@ 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 __always_inline
Do we need the __always_inline? None of the other calls from __switch_to() have it.
+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 (prev32 & !next32)I know they're bools but this is perverse! Why can't it just be: if (next32) val &= ~ARCH_TIMER_USR_VCT_ACCESS_EN; else val |= ARCH_TIMER_USR_VCT_ACCESS_EN; ? Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel