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Fix irq route entries exceeding KVM_MAX_IRQ_ROUTES

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Last month, we experienced several guests crash(6cores-8cores), qemu logs
display the following messages:

qemu-system-x86_64: /build/qemu-2.1.2/kvm-all.c:976:
kvm_irqchip_commit_routes: Assertion `ret == 0' failed.

After analysis and verification, we can confirm it's irq-balance
daemon(in guest) leads to the assertion failure. Start a 8 core guest with
two disks, execute the following scripts will reproduce the BUG quickly:

irq_affinity.sh
========================================================================

vda_irq_num=25
vdb_irq_num=27
while [ 1 ]
do
    for irq in {1,2,4,8,10,20,40,80}
        do
            echo $irq > /proc/irq/$vda_irq_num/smp_affinity
            echo $irq > /proc/irq/$vdb_irq_num/smp_affinity
            dd if=/dev/vda of=/dev/zero bs=4K count=100 iflag=direct
            dd if=/dev/vdb of=/dev/zero bs=4K count=100 iflag=direct
        done
done
========================================================================

QEMU setup static irq route entries in kvm_pc_setup_irq_routing(), PIC and
IOAPIC share the first 15 GSI numbers, take up 23 GSI numbers, but take up
38 irq route entries. When change irq smp_affinity in guest, a dynamic route
entry may be setup, the current logic is: if allocate GSI number succeeds,
a new route entry can be added. The available dynamic GSI numbers is
1021(KVM_MAX_IRQ_ROUTES-23), but available irq route entries is only
986(KVM_MAX_IRQ_ROUTES-38), GSI numbers greater than route entries.
irq-balance's behavior will eventually leads to total irq route entries
exceed KVM_MAX_IRQ_ROUTES, ioctl(KVM_SET_GSI_ROUTING) fail and
kvm_irqchip_commit_routes() trigger assertion failure.

This patch fix the BUG.

Signed-off-by: Wenshuang Ma <kevinnma@tencent.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
马文霜 2015-07-01 15:41:41 +02:00 committed by Paolo Bonzini
parent 41da4bd642
commit bdf026317d
1 changed files with 10 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
kvm-all.c
View File

@ -1099,9 +1099,17 @@ static int kvm_irqchip_get_virq(KVMState *s)
uint32_t *word = s->used_gsi_bitmap; uint32_t *word = s->used_gsi_bitmap;
int max_words = ALIGN(s->gsi_count, 32) / 32; int max_words = ALIGN(s->gsi_count, 32) / 32;
int i, zeroes; int i, zeroes;
bool retry = true;
again: /*
* PIC and IOAPIC share the first 16 GSI numbers, thus the available
* GSI numbers are more than the number of IRQ route. Allocating a GSI
* number can succeed even though a new route entry cannot be added.
* When this happens, flush dynamic MSI entries to free IRQ route entries.
*/
if (!s->direct_msi && s->irq_routes->nr == s->gsi_count) {
kvm_flush_dynamic_msi_routes(s);
}
/* Return the lowest unused GSI in the bitmap */ /* Return the lowest unused GSI in the bitmap */
for (i = 0; i < max_words; i++) { for (i = 0; i < max_words; i++) {
zeroes = ctz32(~word[i]); zeroes = ctz32(~word[i]);
@ -1111,11 +1119,6 @@ again:
return zeroes + i * 32; return zeroes + i * 32;
} }
if (!s->direct_msi && retry) {
retry = false;
kvm_flush_dynamic_msi_routes(s);
goto again;
}
return -ENOSPC; return -ENOSPC;
} }