Re: [PATCH v25 01/12] Linux Random Number Generator

On Sat, 16 Nov 2019, Stephan Müller wrote:

+/**
+ * Hot code path - Callback for interrupt handler
+ */
+void add_interrupt_randomness(int irq, int irq_flags)
+{
+	lrng_time_process();
+
+	if (!lrng_pool_highres_timer()) {
+		struct pt_regs *regs = get_irq_regs();
+		static atomic_t reg_idx = ATOMIC_INIT(0);
+		u64 ip;
+
+		lrng_pool_lfsr_u32(jiffies);
+		lrng_pool_lfsr_u32(irq);
+		lrng_pool_lfsr_u32(irq_flags);
+
+		if (regs) {
+			u32 *ptr = (u32 *)regs;
+			int reg_ptr = atomic_add_return_relaxed(1, &reg_idx);
+			size_t n = (sizeof(struct pt_regs) / sizeof(u32));
+
+			ip = instruction_pointer(regs);
+			lrng_pool_lfsr_u32(*(ptr + (reg_ptr % n)));
+		} else
+			ip = _RET_IP_;
+
+		lrng_pool_lfsr_u32(ip >> 32);
+		lrng_pool_lfsr_u32(ip);
+	}

Is there a way to avoid all that processing right in the interrupt hot
path and just store the raw data for later processing?

Thanks,

	tglx