x86: MSI start irq numbering from nr_irqs_gsi

Impact: sanitize MSI irq number ordering from top-down to bottom-up

Increase new MSI IRQs starting from nr_irqs_gsi (which is somewhere below
256), instead of decreasing from NR_IRQS. (The latter method can result
in confusingly high IRQ numbers - if NR_CPUS is set to a high value and
NR_IRQS scales up to a high value.)

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

3 files changed, 19 insertions, 9 deletions

diff --git a/arch/x86/include/asm/io_apic.h b/arch/x86/include/asm/io_apic.h
index 6afd9933a7dd..b35e94c2d6df 100644
--- a/arch/x86/include/asm/io_apic.h
+++ b/arch/x86/include/asm/io_apic.h
@@ -188,7 +188,7 @@ extern void restore_IO_APIC_setup(void);
 extern void reinit_intr_remapped_IO_APIC(int);
 #endif
 
-extern int probe_nr_irqs(void);
+extern void probe_nr_irqs_gsi(void);
 
 #else  /* !CONFIG_X86_IO_APIC */
 #define io_apic_assign_pci_irqs 0
diff --git a/arch/x86/kernel/io_apic.c b/arch/x86/kernel/io_apic.c
index 9870461ae933..0dcde74abd1d 100644
--- a/arch/x86/kernel/io_apic.c
+++ b/arch/x86/kernel/io_apic.c
@@ -2973,7 +2973,7 @@ unsigned int create_irq_nr(unsigned int irq_want)
 
         irq = 0;
         spin_lock_irqsave(&vector_lock, flags);
-        for (new = irq_want; new > 0; new--) {
+        for (new = irq_want; new < NR_IRQS; new++) {
                 if (platform_legacy_irq(new))
                         continue;
 
@@ -3001,11 +3001,14 @@ unsigned int create_irq_nr(unsigned int irq_want)
         return irq;
 }
 
+static int nr_irqs_gsi = NR_IRQS_LEGACY;
 int create_irq(void)
 {
+        unsigned int irq_want;
         int irq;
 
-        irq = create_irq_nr(nr_irqs - 1);
+        irq_want = nr_irqs_gsi;
+        irq = create_irq_nr(irq_want);
 
         if (irq == 0)
                 irq = -1;
@@ -3281,7 +3284,7 @@ int arch_setup_msi_irq(struct pci_dev *dev, struct msi_desc *msidesc)
         int ret;
         unsigned int irq_want;
 
-        irq_want = nr_irqs - 1;
+        irq_want = nr_irqs_gsi;
         irq = create_irq_nr(irq_want);
         if (irq == 0)
                 return -1;
@@ -3321,11 +3324,11 @@ int arch_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
         int index = 0;
 #endif
 
-        irq_want = nr_irqs - 1;
+        irq_want = nr_irqs_gsi;
         sub_handle = 0;
         list_for_each_entry(msidesc, &dev->msi_list, list) {
                 irq = create_irq_nr(irq_want);
-                irq_want--;
+                irq_want++;
                 if (irq == 0)
                         return -1;
 #ifdef CONFIG_INTR_REMAP
@@ -3674,9 +3677,16 @@ int __init io_apic_get_redir_entries (int ioapic)
         return reg_01.bits.entries;
 }
 
-int __init probe_nr_irqs(void)
+void __init probe_nr_irqs_gsi(void)
 {
-        return NR_IRQS;
+        int idx;
+        int nr = 0;
+
+        for (idx = 0; idx < nr_ioapics; idx++)
+                nr += io_apic_get_redir_entries(idx) + 1;
+
+        if (nr > nr_irqs_gsi)
+                nr_irqs_gsi = nr;
 }
 
 /* --------------------------------------------------------------------------
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 9d5674f7b6cc..a3834f123206 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1082,7 +1082,7 @@ void __init setup_arch(char **cmdline_p)
         ioapic_init_mappings();
 
         /* need to wait for io_apic is mapped */
-        nr_irqs = probe_nr_irqs();
+        probe_nr_irqs_gsi();
 
         kvm_guest_init();