linux-kernel - [PATCH v2 4/8] x86/ioapic: Handle Extended Destination ID field in RTE

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Date:   Fri,  9 Oct 2020 11:46:12 +0100
From:   David Woodhouse <dwmw2@...radead.org>
To:     x86@...nel.org
Cc:     kvm <kvm@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>,
        Paolo Bonzini <pbonzini@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-hyperv@...r.kernel.org
Subject: [PATCH v2 4/8] x86/ioapic: Handle Extended Destination ID field in RTE

From: David Woodhouse <dwmw@...zon.co.uk>

Bits 63-48 of the I/OAPIC Redirection Table Entry map directly to
bits 19-4 of the address used in the resulting MSI cycle.

Historically, the x86 MSI format only used the top 8 of those 16 bits as
the destination APIC ID, and the "Extended Destination ID" in the lower
8 bits was unused.

With interrupt remapping, the lowest bit of the Extended Destination ID
(bit 48 of RTE, bit 4 of MSI address) is now used to indicate a
remappable format MSI.

A hypervisor can use the other 7 bits of the Extended Destination ID to
permit guests to address up to 15 bits of APIC IDs, thus allowing 32768
vCPUs before having to expose a vIOMMU and interrupt remapping to the
guest.

This enlightenment could theoretically be transparent to the I/OAPIC
code if it were always generating its RTE from an MSI message created by
the parent irqchip. That cleanup will happen separately but doesn't cover
all cases — for the ExtINT hackery and restoring boot mode, RTEs are
still generated locally. So we have to teach the I/OAPIC about the
ext_dest bits anyway.

No behavioural change in this patch, since nothing yet permits APIC IDs
above 255 to be used with the non-IR I/OAPIC domain.

Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
---
 arch/x86/include/asm/io_apic.h |  3 ++-
 arch/x86/kernel/apic/io_apic.c | 19 +++++++++++++------
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/io_apic.h b/arch/x86/include/asm/io_apic.h
index a1a26f6d3aa4..5bb3cf4ff2fd 100644
--- a/arch/x86/include/asm/io_apic.h
+++ b/arch/x86/include/asm/io_apic.h
@@ -78,7 +78,8 @@ struct IO_APIC_route_entry {
 		mask		:  1,	/* 0: enabled, 1: disabled */
 		__reserved_2	: 15;
 
-	__u32	__reserved_3	: 24,
+	__u32	__reserved_3	: 17,
+		virt_ext_dest	:  7,
 		dest		:  8;
 } __attribute__ ((packed));
 
diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index a33380059db6..54f6a029b1d1 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -1239,10 +1239,10 @@ static void io_apic_print_entries(unsigned int apic, unsigned int nr_entries)
 			       buf, (ir_entry->index2 << 15) | ir_entry->index,
 			       ir_entry->zero);
 		else
-			printk(KERN_DEBUG "%s, %s, D(%02X), M(%1d)\n",
+			printk(KERN_DEBUG "%s, %s, D(%02X%02X), M(%1d)\n",
 			       buf,
 			       entry.dest_mode == IOAPIC_DEST_MODE_LOGICAL ?
-			       "logical " : "physical",
+			       "logical " : "physical", entry.virt_ext_dest,
 			       entry.dest, entry.delivery_mode);
 	}
 }
@@ -1410,6 +1410,7 @@ void native_restore_boot_irq_mode(void)
 	 */
 	if (ioapic_i8259.pin != -1) {
 		struct IO_APIC_route_entry entry;
+		u32 apic_id = read_apic_id();
 
 		memset(&entry, 0, sizeof(entry));
 		entry.mask		= IOAPIC_UNMASKED;
@@ -1417,7 +1418,8 @@ void native_restore_boot_irq_mode(void)
 		entry.polarity		= IOAPIC_POL_HIGH;
 		entry.dest_mode		= IOAPIC_DEST_MODE_PHYSICAL;
 		entry.delivery_mode	= dest_ExtINT;
-		entry.dest		= read_apic_id();
+		entry.dest		= apic_id & 0xff;
+		entry.virt_ext_dest	= apic_id >> 8;
 
 		/*
 		 * Add it to the IO-APIC irq-routing table:
@@ -1861,7 +1863,8 @@ static void ioapic_configure_entry(struct irq_data *irqd)
 	 * ioapic chip to verify that.
 	 */
 	if (irqd->chip == &ioapic_chip) {
-		mpd->entry.dest = cfg->dest_apicid;
+		mpd->entry.dest = cfg->dest_apicid & 0xff;
+		mpd->entry.virt_ext_dest = cfg->dest_apicid >> 8;
 		mpd->entry.vector = cfg->vector;
 	}
 	for_each_irq_pin(entry, mpd->irq_2_pin)
@@ -2027,6 +2030,7 @@ static inline void __init unlock_ExtINT_logic(void)
 	int apic, pin, i;
 	struct IO_APIC_route_entry entry0, entry1;
 	unsigned char save_control, save_freq_select;
+	u32 apic_id;
 
 	pin  = find_isa_irq_pin(8, mp_INT);
 	if (pin == -1) {
@@ -2042,11 +2046,13 @@ static inline void __init unlock_ExtINT_logic(void)
 	entry0 = ioapic_read_entry(apic, pin);
 	clear_IO_APIC_pin(apic, pin);
 
+	apic_id = hard_smp_processor_id();
 	memset(&entry1, 0, sizeof(entry1));
 
 	entry1.dest_mode = IOAPIC_DEST_MODE_PHYSICAL;
 	entry1.mask = IOAPIC_UNMASKED;
-	entry1.dest = hard_smp_processor_id();
+	entry1.dest = apic_id & 0xff;
+	entry1.virt_ext_dest = apic_id >> 8;
 	entry1.delivery_mode = dest_ExtINT;
 	entry1.polarity = entry0.polarity;
 	entry1.trigger = IOAPIC_EDGE;
@@ -2949,7 +2955,8 @@ static void mp_setup_entry(struct irq_cfg *cfg, struct mp_chip_data *data,
 	memset(entry, 0, sizeof(*entry));
 	entry->delivery_mode = apic->irq_delivery_mode;
 	entry->dest_mode     = apic->irq_dest_mode;
-	entry->dest	     = cfg->dest_apicid;
+	entry->dest	     = cfg->dest_apicid & 0xff;
+	entry->virt_ext_dest = cfg->dest_apicid >> 8;
 	entry->vector	     = cfg->vector;
 	entry->trigger	     = data->trigger;
 	entry->polarity	     = data->polarity;
-- 
2.26.2