Re: [PATCH 1/2] arm64: Move handling of erratum 1418040 into C code
From: Stephen Boyd <hidden>
Date: 2020-07-28 20:05:51
Quoting Marc Zyngier (2020-07-28 02:21:11)
quoted hunk ↗ jump to hunk
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. - */
Can this comment go above the function in C?
quoted hunk ↗ jump to hunk
-#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_CONTEXTIDRdiff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index 6089638c7d43..87c33f7c536b 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c@@ -515,6 +515,34 @@ static void entry_task_switch(struct task_struct *next) __this_cpu_write(__entry_task, next); } +static void erratum_1418040_thread_switch(struct task_struct *prev,
Should it be marked __always_inline so that the cpus_have_const_cap() check can avoid the branch to this function when there's nothing to do?
+ 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 = (!(prev->flags & PF_KTHREAD) &&
+ is_compat_thread(task_thread_info(prev)));
+ next32 = (!(next->flags & PF_KTHREAD) &&
+ is_compat_thread(task_thread_info(next)));
+
+ if (prev32 == next32)
+ return;
+
+ val = read_sysreg(cntkctl_el1);
+
+ if (prev32 & !next32)
+ val |= ARCH_TIMER_USR_VCT_ACCESS_EN;
+ else
+ val &= ~ARCH_TIMER_USR_VCT_ACCESS_EN;
+
+ write_sysreg(val, cntkctl_el1);
+}
+
/*
* Thread switching.
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