Re: [PATCH v2 2/2] KVM: x86: Add lowest-priority support for vt-d posted-interrupts
From: Yang Zhang
Date: Sun Dec 20 2015 - 21:02:09 EST
On 2015/12/21 9:55, Wu, Feng wrote:
-----Original Message-----
From: linux-kernel-owner@xxxxxxxxxxxxxxx [mailto:linux-kernel-
owner@xxxxxxxxxxxxxxx] On Behalf Of Yang Zhang
Sent: Monday, December 21, 2015 9:50 AM
To: Wu, Feng <feng.wu@xxxxxxxxx>; pbonzini@xxxxxxxxxx;
rkrcmar@xxxxxxxxxx
Cc: kvm@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
Subject: Re: [PATCH v2 2/2] KVM: x86: Add lowest-priority support for vt-d
posted-interrupts
On 2015/12/16 9:37, Feng Wu wrote:
Use vector-hashing to deliver lowest-priority interrupts for
VT-d posted-interrupts.
Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
---
arch/x86/kvm/lapic.c | 67
++++++++++++++++++++++++++++++++++++++++++++++++++++
arch/x86/kvm/lapic.h | 2 ++
arch/x86/kvm/vmx.c | 12 ++++++++--
3 files changed, 79 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index e29001f..d4f2c8f 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -854,6 +854,73 @@ out:
}
/*
+ * This routine handles lowest-priority interrupts using vector-hashing
+ * mechanism. As an example, modern Intel CPUs use this method to handle
+ * lowest-priority interrupts.
+ *
+ * Here is the details about the vector-hashing mechanism:
+ * 1. For lowest-priority interrupts, store all the possible destination
+ * vCPUs in an array.
+ * 2. Use "guest vector % max number of destination vCPUs" to find the right
+ * destination vCPU in the array for the lowest-priority interrupt.
+ */
+struct kvm_vcpu *kvm_intr_vector_hashing_dest(struct kvm *kvm,
+ struct kvm_lapic_irq *irq)
+{
+ struct kvm_apic_map *map;
+ struct kvm_vcpu *vcpu = NULL;
+
+ if (irq->shorthand)
+ return NULL;
+
+ rcu_read_lock();
+ map = rcu_dereference(kvm->arch.apic_map);
+
+ if (!map)
+ goto out;
+
+ if ((irq->dest_mode != APIC_DEST_PHYSICAL) &&
+ kvm_lowest_prio_delivery(irq)) {
+ u16 cid;
+ int i, idx = 0;
+ unsigned long bitmap = 1;
+ unsigned int dest_vcpus = 0;
+ struct kvm_lapic **dst = NULL;
+
+
+ if (!kvm_apic_logical_map_valid(map))
+ goto out;
+
+ apic_logical_id(map, irq->dest_id, &cid, (u16 *)&bitmap);
+
+ if (cid >= ARRAY_SIZE(map->logical_map))
+ goto out;
+
+ dst = map->logical_map[cid];
+
+ for_each_set_bit(i, &bitmap, 16) {
+ if (!dst[i] && !kvm_lapic_enabled(dst[i]->vcpu)) {
+ clear_bit(i, &bitmap);
+ continue;
+ }
+ }
+
+ dest_vcpus = hweight16(bitmap);
+
+ if (dest_vcpus != 0) {
+ idx = kvm_vector_2_index(irq->vector, dest_vcpus,
+ &bitmap, 16);
+ vcpu = dst[idx-1]->vcpu;
+ }
+ }
+
+out:
+ rcu_read_unlock();
+ return vcpu;
+}
+EXPORT_SYMBOL_GPL(kvm_intr_vector_hashing_dest);
+
+/*
* Add a pending IRQ into lapic.
* Return 1 if successfully added and 0 if discarded.
*/
diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index 6890ef0..52bffce 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -172,4 +172,6 @@ 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);
+struct kvm_vcpu *kvm_intr_vector_hashing_dest(struct kvm *kvm,
+ struct kvm_lapic_irq *irq);
#endif
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 5eb56ed..3f89189 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -10702,8 +10702,16 @@ static int vmx_update_pi_irte(struct kvm *kvm,
unsigned int host_irq,
*/
kvm_set_msi_irq(e, &irq);
- if (!kvm_intr_is_single_vcpu(kvm, &irq, &vcpu))
- continue;
+
+ if (!kvm_intr_is_single_vcpu(kvm, &irq, &vcpu)) {
+ if (!kvm_vector_hashing_enabled() ||
+ irq.delivery_mode !=
APIC_DM_LOWEST)
+ continue;
+
+ vcpu = kvm_intr_vector_hashing_dest(kvm, &irq);
+ if (!vcpu)
+ continue;
+ }
I am a little confused with the 'continue'. If the destination is not
single vcpu, shouldn't we rollback to use non-PI mode?
Here is the logic:
- If it is single destination, we will use PI no matter it is fixed or lowest-priority.
- If it is not single destination:
a) It is fixed, we will use non-PI
b) It is lowest-priority and vector-hashing is enabled, we will use PI
c) otherwise, use non-PI
If it is single destination previously, then change to no-single mode.
Can current code cover this case?
Thanks,
Feng
vcpu_info.pi_desc_addr = __pa(vcpu_to_pi_desc(vcpu));
vcpu_info.vector = irq.vector;
--
best regards
yang
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--
best regards
yang
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