arch/x86_64: do not modify CR8 in interrupt path (37929b34) · Commits · Wenxi XU / zephyr

Currently, the interrupt service code manually raises the CPU task priority to the priority level of the vector being serviced to defer any lower-priority interrupts. This is unnecessary; the local APIC is aware that an interrupt is in-service and accounts for its priority when deciding whether to issue an overriding interrupt to the CPU. Signed-off-by:

Charles E. Youse <charles@gnuless.org>

arch/x86_64/core/xuk.c

+2 −13

Original line number	Diff line number	Diff line
		@@ -176,15 +176,7 @@ long _isr_c_top(unsigned long vecret, unsigned long rsp,

		z_isr_entry();

		/* Set current priority in CR8 to the currently-serviced IRQ
		* and re-enable interrupts
		*/
		unsigned long long cr8, cr8new = vector >> 4;

		__asm__ volatile("movq %%cr8, %0;"
		"movq %1, %%cr8;"
		"sti"
		: "=r"(cr8) : "r"(cr8new));
		__asm__ volatile("sti"); /* re-enable interrupts */

		if (h->fn) {
		h->fn(h->arg, err);
		@@ -192,10 +184,7 @@ long _isr_c_top(unsigned long vecret, unsigned long rsp,
		z_unhandled_vector(vector, err, frame);
		}

		/* Mask interrupts to finish processing (they'll get restored
		* in the upcoming IRET) and restore CR8
		*/
		__asm__ volatile("cli; movq %0, %%cr8" : : "r"(cr8));
		__asm__ volatile("cli"); /* mask [at least] until upcoming IRET */

		/* Signal EOI if it's an APIC-managed interrupt */
		if (vector > 0x1f) {

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