[RFC PATCH v3 30/32] x86/fred: allow FRED systems to use interrupt vectors 0x10-0x1f

Xin Li
2023-02-24T07:30:06Z

FRED inherits the Intel VT-x enhancement of classified events with
a two-level event dispatch logic. The first-level dispatch is on
the event type, and the second-level is on the event vector. This
also means that vectors in different event types are orthogonal,
thus, vectors 0x10-0x1f become available as hardware interrupts.

Enable interrupt vectors 0x10-0x1f on FRED systems (interrupt 0x80 is
already enabled.) Most of these changes are about removing the
assumption that the lowest-priority vector is hard-wired to 0x20.

Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: Xin Li <xin3.li@intel.com>
---
arch/x86/include/asm/idtentry.h | 4 ++--
arch/x86/include/asm/irq.h | 5 +++++
arch/x86/include/asm/irq_vectors.h | 15 +++++++++++----
arch/x86/kernel/apic/apic.c | 11 ++++++++---
arch/x86/kernel/apic/vector.c | 8 +++++++-
arch/x86/kernel/fred.c | 4 ++--
arch/x86/kernel/idt.c | 6 +++---
arch/x86/kernel/irq.c | 2 +-
arch/x86/kernel/traps.c | 2 ++
9 files changed, 41 insertions(+), 16 deletions(-)

diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index 7f70ca6f0020..bdfd15ac1311 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -546,8 +546,8 @@ __visible noinstr void func(struct pt_regs *regs, \
*/
.align IDT_ALIGN
SYM_CODE_START(irq_entries_start)
- vector=FIRST_EXTERNAL_VECTOR
- .rept NR_EXTERNAL_VECTORS
+ vector=FIRST_EXTERNAL_VECTOR_IDT
+ .rept FIRST_SYSTEM_VECTOR - FIRST_EXTERNAL_VECTOR_IDT
UNWIND_HINT_IRET_REGS
0 :
ENDBR
diff --git a/arch/x86/include/asm/irq.h b/arch/x86/include/asm/irq.h
index 768aa234cbb4..e4be6f8409ad 100644
--- a/arch/x86/include/asm/irq.h
+++ b/arch/x86/include/asm/irq.h
@@ -11,6 +11,11 @@
#include <asm/apicdef.h>
#include <asm/irq_vectors.h>

+/*
+ * The first available IRQ vector
+ */
+extern unsigned int __ro_after_init first_external_vector;
+
/*
* The irq entry code is in the noinstr section and the start/end of
* __irqentry_text is emitted via labels. Make the build fail if
diff --git a/arch/x86/include/asm/irq_vectors.h b/arch/x86/include/asm/irq_vectors.h
index 43dcb9284208..cb3670a7c18f 100644
--- a/arch/x86/include/asm/irq_vectors.h
+++ b/arch/x86/include/asm/irq_vectors.h
@@ -31,15 +31,23 @@

/*
* IDT vectors usable for external interrupt sources start at 0x20.
- * (0x80 is the syscall vector, 0x30-0x3f are for ISA)
+ * (0x80 is the syscall vector, 0x30-0x3f are for ISA).
+ *
+ * With FRED we can also use 0x10-0x1f even though those overlap
+ * exception vectors as FRED distinguishes exceptions and interrupts.
+ * Therefore, FIRST_EXTERNAL_VECTOR is no longer a constant.
*/
-#define FIRST_EXTERNAL_VECTOR 0x20
+#define FIRST_EXTERNAL_VECTOR_IDT 0x20
+#define FIRST_EXTERNAL_VECTOR_FRED 0x10
+#define FIRST_EXTERNAL_VECTOR first_external_vector

/*
* Reserve the lowest usable vector (and hence lowest priority) 0x20 for
* triggering cleanup after irq migration. 0x21-0x2f will still be used
* for device interrupts.
*/
+#define IRQ_MOVE_CLEANUP_VECTOR_IDT FIRST_EXTERNAL_VECTOR_IDT
+#define IRQ_MOVE_CLEANUP_VECTOR_FRED FIRST_EXTERNAL_VECTOR_FRED
#define IRQ_MOVE_CLEANUP_VECTOR FIRST_EXTERNAL_VECTOR

#define IA32_SYSCALL_VECTOR 0x80
@@ -48,7 +56,7 @@
* Vectors 0x30-0x3f are used for ISA interrupts.
* round up to the next 16-vector boundary
*/
-#define ISA_IRQ_VECTOR(irq) (((FIRST_EXTERNAL_VECTOR + 16) & ~15) + irq)
+#define ISA_IRQ_VECTOR(irq) (((FIRST_EXTERNAL_VECTOR_IDT + 16) & ~15) + irq)

/*
* Special IRQ vectors used by the SMP architecture, 0xf0-0xff
@@ -114,7 +122,6 @@
#define FIRST_SYSTEM_VECTOR NR_VECTORS
#endif

-#define NR_EXTERNAL_VECTORS (FIRST_SYSTEM_VECTOR - FIRST_EXTERNAL_VECTOR)
#define NR_SYSTEM_VECTORS (NR_VECTORS - FIRST_SYSTEM_VECTOR)

/*
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 20d9a604da7c..eef67f64aa81 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1621,12 +1621,17 @@ static void setup_local_APIC(void)
/*
* Set Task Priority to 'accept all except vectors 0-31'. An APIC
* vector in the 16-31 range could be delivered if TPR == 0, but we
- * would think it's an exception and terrible things will happen. We
- * never change this later on.
+ * would think it's an exception and terrible things will happen,
+ * unless we are using FRED in which case interrupts and
+ * exceptions are distinguished by type code.
+ *
+ * We never change this later on.
*/
+ BUG_ON(!first_external_vector);
+
value = apic_read(APIC_TASKPRI);
value &= ~APIC_TPRI_MASK;
- value |= 0x10;
+ value |= (first_external_vector - 0x10) & APIC_TPRI_MASK;
apic_write(APIC_TASKPRI, value);

/* Clear eventually stale ISR/IRR bits */
diff --git a/arch/x86/kernel/apic/vector.c b/arch/x86/kernel/apic/vector.c
index c1efebd27e6c..f4325445fd78 100644
--- a/arch/x86/kernel/apic/vector.c
+++ b/arch/x86/kernel/apic/vector.c
@@ -46,6 +46,7 @@ static struct irq_matrix *vector_matrix;
#ifdef CONFIG_SMP
static DEFINE_PER_CPU(struct hlist_head, cleanup_list);
#endif
+unsigned int first_external_vector = FIRST_EXTERNAL_VECTOR_IDT;

void lock_vector_lock(void)
{
@@ -796,7 +797,12 @@ int __init arch_early_irq_init(void)
* Allocate the vector matrix allocator data structure and limit the
* search area.
*/
- vector_matrix = irq_alloc_matrix(NR_VECTORS, FIRST_EXTERNAL_VECTOR,
+ if (cpu_feature_enabled(X86_FEATURE_FRED))
+ first_external_vector = FIRST_EXTERNAL_VECTOR_FRED;
+ else
+ first_external_vector = FIRST_EXTERNAL_VECTOR_IDT;
+
+ vector_matrix = irq_alloc_matrix(NR_VECTORS, first_external_vector,
FIRST_SYSTEM_VECTOR);
BUG_ON(!vector_matrix);

diff --git a/arch/x86/kernel/fred.c b/arch/x86/kernel/fred.c
index 827b58fd98d4..04f057219c6e 100644
--- a/arch/x86/kernel/fred.c
+++ b/arch/x86/kernel/fred.c
@@ -51,7 +51,7 @@ void __init fred_setup_apic(void)
{
int i;

- for (i = 0; i < FIRST_EXTERNAL_VECTOR; i++)
+ for (i = 0; i < FIRST_EXTERNAL_VECTOR_FRED; i++)
set_bit(i, system_vectors);

/*
@@ -60,7 +60,7 @@ void __init fred_setup_apic(void)
* /proc/interrupts.
*/
#ifdef CONFIG_SMP
- set_bit(IRQ_MOVE_CLEANUP_VECTOR, system_vectors);
+ set_bit(IRQ_MOVE_CLEANUP_VECTOR_FRED, system_vectors);
#endif

for (i = 0; i < NR_SYSTEM_VECTORS; i++) {
diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c
index a58c6bc1cd68..d3fd86f85de9 100644
--- a/arch/x86/kernel/idt.c
+++ b/arch/x86/kernel/idt.c
@@ -131,7 +131,7 @@ static const __initconst struct idt_data apic_idts[] = {
INTG(RESCHEDULE_VECTOR, asm_sysvec_reschedule_ipi),
INTG(CALL_FUNCTION_VECTOR, asm_sysvec_call_function),
INTG(CALL_FUNCTION_SINGLE_VECTOR, asm_sysvec_call_function_single),
- INTG(IRQ_MOVE_CLEANUP_VECTOR, asm_sysvec_irq_move_cleanup),
+ INTG(IRQ_MOVE_CLEANUP_VECTOR_IDT, asm_sysvec_irq_move_cleanup),
INTG(REBOOT_VECTOR, asm_sysvec_reboot),
#endif

@@ -274,13 +274,13 @@ static void __init idt_map_in_cea(void)
*/
void __init idt_setup_apic_and_irq_gates(void)
{
- int i = FIRST_EXTERNAL_VECTOR;
+ int i = FIRST_EXTERNAL_VECTOR_IDT;
void *entry;

idt_setup_from_table(idt_table, apic_idts, ARRAY_SIZE(apic_idts), true);

for_each_clear_bit_from(i, system_vectors, FIRST_SYSTEM_VECTOR) {
- entry = irq_entries_start + IDT_ALIGN * (i - FIRST_EXTERNAL_VECTOR);
+ entry = irq_entries_start + IDT_ALIGN * (i - FIRST_EXTERNAL_VECTOR_IDT);
set_intr_gate(i, entry);
}

diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
index 7e125fff45ab..b7511e02959c 100644
--- a/arch/x86/kernel/irq.c
+++ b/arch/x86/kernel/irq.c
@@ -359,7 +359,7 @@ void fixup_irqs(void)
* vector_lock because the cpu is already marked !online, so
* nothing else will touch it.
*/
- for (vector = FIRST_EXTERNAL_VECTOR; vector < NR_VECTORS; vector++) {
+ for (vector = first_external_vector; vector < NR_VECTORS; vector++) {
if (IS_ERR_OR_NULL(__this_cpu_read(vector_irq[vector])))
continue;

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index c7253b4901f0..c46eba091728 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -1544,6 +1544,8 @@ DEFINE_IDTENTRY_IRQ(spurious_interrupt)
pr_info("Spurious interrupt (vector 0x%x) on CPU#%d, should never happen.\n",
vector, smp_processor_id());
}
+
+unsigned int first_external_vector = FIRST_EXTERNAL_VECTOR_IDT;
#endif

/*
--
2.34.1