Re: [PATCH v3 2/4] KVM: x86: Use vector-hashing to deliver lowest-priority interrupts

From: Yang Zhang
Date: Thu Jan 21 2016 - 00:23:57 EST

On 2016/1/20 9:42, Feng Wu wrote:
Use vector-hashing to deliver lowest-priority interrupts, As an
example, modern Intel CPUs in server platform use this method to
handle lowest-priority interrupts.

Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
---
v3:
- Fix a bug for sparse topologies, in that case, vcpu_id is not equal
to the return value got by kvm_get_vcpu().
- Remove unnecessary check in fast irq delivery patch.
- print a error message only once for each guest when we find hardware
disabled LAPIC during interrupt injection.

arch/x86/include/asm/kvm_host.h | 2 ++
arch/x86/kvm/irq_comm.c | 27 +++++++++++++++++----
arch/x86/kvm/lapic.c | 52 ++++++++++++++++++++++++++++++++++++++---
arch/x86/kvm/lapic.h | 2 ++
arch/x86/kvm/x86.c | 9 +++++++
arch/x86/kvm/x86.h | 1 +
6 files changed, 85 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 44adbb8..5054810 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -754,6 +754,8 @@ struct kvm_arch {

bool irqchip_split;
u8 nr_reserved_ioapic_pins;
+
+ int disabled_lapic_found;
};

struct kvm_vm_stat {
diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
index 8fc89ef..062e907 100644
--- a/arch/x86/kvm/irq_comm.c
+++ b/arch/x86/kvm/irq_comm.c
@@ -34,6 +34,7 @@
#include "lapic.h"

#include "hyperv.h"
+#include "x86.h"

static int kvm_set_pic_irq(struct kvm_kernel_irq_routing_entry *e,
struct kvm *kvm, int irq_source_id, int level,
@@ -55,8 +56,10 @@ static int kvm_set_ioapic_irq(struct kvm_kernel_irq_routing_entry *e,
int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
struct kvm_lapic_irq *irq, unsigned long *dest_map)
{
- int i, r = -1;
+ int i, r = -1, idx = 0;
struct kvm_vcpu *vcpu, *lowest = NULL;
+ unsigned long dest_vcpu_bitmap[BITS_TO_LONGS(KVM_MAX_VCPUS)];
+ unsigned int dest_vcpus = 0;

if (irq->dest_mode == 0 && irq->dest_id == 0xff &&
kvm_lowest_prio_delivery(irq)) {
@@ -67,6 +70,8 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
if (kvm_irq_delivery_to_apic_fast(kvm, src, irq, &r, dest_map))
return r;

+ memset(dest_vcpu_bitmap, 0, sizeof(dest_vcpu_bitmap));
+
kvm_for_each_vcpu(i, vcpu, kvm) {
if (!kvm_apic_present(vcpu))
continue;
@@ -80,13 +85,25 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
r = 0;
r += kvm_apic_set_irq(vcpu, irq, dest_map);
} else if (kvm_lapic_enabled(vcpu)) {
- if (!lowest)
- lowest = vcpu;
- else if (kvm_apic_compare_prio(vcpu, lowest) < 0)
- lowest = vcpu;
+ if (!kvm_vector_hashing_enabled()) {
+ if (!lowest)
+ lowest = vcpu;
+ else if (kvm_apic_compare_prio(vcpu, lowest) < 0)
+ lowest = vcpu;
+ } else {
+ __set_bit(i, dest_vcpu_bitmap);
+ dest_vcpus++;
+ }
}
}

+ if (dest_vcpus != 0) {
+ idx = kvm_vector_2_index(irq->vector, dest_vcpus,
+ dest_vcpu_bitmap, KVM_MAX_VCPUS);
+
+ lowest = kvm_get_vcpu(kvm, idx - 1);
+ }
+
if (lowest)
r = kvm_apic_set_irq(lowest, irq, dest_map);

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 36591fa..e1a449da 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -675,6 +675,22 @@ bool kvm_apic_match_dest(struct kvm_vcpu *vcpu, struct kvm_lapic *source,
}
}

+int kvm_vector_2_index(u32 vector, u32 dest_vcpus,
+ const unsigned long *bitmap, u32 bitmap_size)
+{
+ u32 mod;
+ int i, idx = 0;
+
+ mod = vector % dest_vcpus;
+
+ for (i = 0; i <= mod; i++) {
+ idx = find_next_bit(bitmap, bitmap_size, idx) + 1;
+ BUG_ON(idx > bitmap_size);
+ }
+
+ return idx;
+}
+
bool kvm_irq_delivery_to_apic_fast(struct kvm *kvm, struct kvm_lapic *src,
struct kvm_lapic_irq *irq, int *r, unsigned long *dest_map)
{
@@ -727,21 +743,51 @@ bool kvm_irq_delivery_to_apic_fast(struct kvm *kvm, struct kvm_lapic *src,

dst = map->logical_map[cid];

- if (kvm_lowest_prio_delivery(irq)) {
+ if (!kvm_lowest_prio_delivery(irq))
+ goto set_irq;
+
+ if (!kvm_vector_hashing_enabled()) {
int l = -1;
for_each_set_bit(i, &bitmap, 16) {
if (!dst[i])
continue;
if (l < 0)
l = i;
- else if (kvm_apic_compare_prio(dst[i]->vcpu, dst[l]->vcpu) < 0)
+ else if (kvm_apic_compare_prio(dst[i]->vcpu,
+ dst[l]->vcpu) < 0)
l = i;
}
-
bitmap = (l >= 0) ? 1 << l : 0;
+ } else {
+ int idx = 0;
+ unsigned int dest_vcpus = 0;
+
+ dest_vcpus = hweight16(bitmap);
+ if (dest_vcpus == 0)
+ goto out;
+
+ idx = kvm_vector_2_index(irq->vector,
+ dest_vcpus, &bitmap, 16);
+
+ /*
+ * We may find a hardware disabled LAPIC here, if that
+ * is the case, print out a error message once for each
+ * guest and return.
+ */
+ if (!dst[idx-1] &&
+ (kvm->arch.disabled_lapic_found == 0)) {
+ kvm->arch.disabled_lapic_found = 1;
+ printk(KERN_ERR
+ "Disabled LAPIC found during irq injection\n");
+ goto out;

What does "goto out" mean? Inject successfully or fail? According the value of ret which is set to ture here, it means inject successfully but i = -1.

+ }
+
+ bitmap = 0;
+ __set_bit(idx-1, &bitmap);

We can reuse the code like:
bitmap = (idx > 0) ? 1 << (idx - 1) : 0;

}
}

+set_irq:
for_each_set_bit(i, &bitmap, 16) {
if (!dst[i])
continue;
diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index 41bdb35..d864601 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -175,4 +175,6 @@ void wait_lapic_expire(struct kvm_vcpu *vcpu);

bool kvm_intr_is_single_vcpu_fast(struct kvm *kvm, struct kvm_lapic_irq *irq,
struct kvm_vcpu **dest_vcpu);
+int kvm_vector_2_index(u32 vector, u32 dest_vcpus,
+ const unsigned long *bitmap, u32 bitmap_size);
#endif
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4244c2b..47daf77 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -123,6 +123,9 @@ module_param(tsc_tolerance_ppm, uint, S_IRUGO | S_IWUSR);
unsigned int __read_mostly lapic_timer_advance_ns = 0;
module_param(lapic_timer_advance_ns, uint, S_IRUGO | S_IWUSR);

+bool __read_mostly enable_vector_hashing = 1;
+module_param(enable_vector_hashing, bool, S_IRUGO);
+
static bool __read_mostly backwards_tsc_observed = false;

#define KVM_NR_SHARED_MSRS 16
@@ -8370,6 +8373,12 @@ int kvm_arch_update_irqfd_routing(struct kvm *kvm, unsigned int host_irq,
return kvm_x86_ops->update_pi_irte(kvm, host_irq, guest_irq, set);
}

+bool kvm_vector_hashing_enabled(void)
+{
+ return enable_vector_hashing;
+}
+EXPORT_SYMBOL_GPL(kvm_vector_hashing_enabled);
+
EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_exit);
EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_fast_mmio);
EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_inj_virq);
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index f2afa5f..04bd0f9 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -179,6 +179,7 @@ int kvm_mtrr_set_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data);
int kvm_mtrr_get_msr(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata);
bool kvm_mtrr_check_gfn_range_consistency(struct kvm_vcpu *vcpu, gfn_t gfn,
int page_num);
+bool kvm_vector_hashing_enabled(void);

#define KVM_SUPPORTED_XCR0 (XFEATURE_MASK_FP | XFEATURE_MASK_SSE \
| XFEATURE_MASK_YMM | XFEATURE_MASK_BNDREGS \



--
best regards
yang