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In a subsequent patch, we will relax the kernel mode NEON policy, and permit kernel mode NEON to be used not only from task context, as is permitted today, but also from softirq context. Given that softirqs may trigger over the back of any IRQ unless they are explicitly disabled, we need to address the resulting races in the VFP state handling, by disabling softirq processing in two distinct but related cases: - kernel mode NEON will leave the FPU disabled after it completes, so any kernel code sequence that enables the FPU and subsequently accesses its registers needs to disable softirqs until it completes; - kernel_neon_begin() will preserve the userland VFP state in memory, and if it interrupts the ordinary VFP state preserve sequence, the latter will resume execution with the VFP registers corrupted, and happily continue saving them to memory. Given that disabling softirqs also disables preemption, we can replace the existing preempt_disable/enable occurrences in the VFP state handling asm code with new macros that dis/enable softirqs instead. In the VFP state handling C code, add local_bh_disable/enable() calls in those places where the VFP state is preserved. One thing to keep in mind is that, once we allow NEON use in softirq context, the result of any such interruption is that the FPEXC_EN bit in the FPEXC register will be cleared, and vfp_current_hw_state[cpu] will be NULL. This means that any sequence that [conditionally] clears FPEXC_EN and/or sets vfp_current_hw_state[cpu] to NULL does not need to run with softirqs disabled, as the result will be the same. Furthermore, the handling of THREAD_NOTIFY_SWITCH is guaranteed to run with IRQs disabled, and so it does not need protection from softirq interruptions either. Tested-by: Martin Willi <martin@strongswan.org> Reviewed-by: Linus Walleij <linus.walleij@linaro.org> Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk> |
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| .. | ||
| entry.S | ||
| Makefile | ||
| vfp.h | ||
| vfpdouble.c | ||
| vfphw.S | ||
| vfpinstr.h | ||
| vfpmodule.c | ||
| vfpsingle.c | ||