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/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
