Re: [PART2 PATCH v4 10/11] svm: Introduce AMD IOMMU avic_ga_log_notifier

[Suravee Suthikulpanit]

Hi Radim,

On 7/13/16 21:29, Radim KrÄmÃÅ wrote:
> 2016-07-13 08:20-0500, Suravee Suthikulpanit:
> > >From: Suravee Suthikulpanit<Suravee.Suthikulpanit@xxxxxxx>
> > >
> > >This patch introduces avic_ga_log_notifier, which will be called
> > >by IOMMU driver whenever it handles the Guest vAPIC (GA) log entry.
> > >
> > >Signed-off-by: Suravee Suthikulpanit<suravee.suthikulpanit@xxxxxxx>
> > >---
> > >  arch/x86/include/asm/kvm_host.h |  2 ++
> > >  arch/x86/kvm/svm.c              | 68 +++++++++++++++++++++++++++++++++++++++--
> > >  2 files changed, 68 insertions(+), 2 deletions(-)
> > >
> > >diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > >index 69e62862..a9466ad 100644
> > >--- a/arch/x86/include/asm/kvm_host.h
> > >+++ b/arch/x86/include/asm/kvm_host.h
> > >@@ -776,9 +776,11 @@ struct kvm_arch {
> > >  	bool disabled_lapic_found;
> > >
> > >  	/* Struct members for AVIC */
> > >+	u32 avic_vm_id;
> > >  	u32 ldr_mode;
> > >  	struct page *avic_logical_id_table_page;
> > >  	struct page *avic_physical_id_table_page;
> > >+	struct hlist_node hnode;
> > >  };
> > >
> > >  struct kvm_vm_stat {
> > >diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> > >index 16ef31b..1d9f2f6 100644
> > >--- a/arch/x86/kvm/svm.c
> > >+++ b/arch/x86/kvm/svm.c
> > >@@ -34,6 +34,8 @@
> > >  #include <linux/sched.h>
> > >  #include <linux/trace_events.h>
> > >  #include <linux/slab.h>
> > >+#include <linux/amd-iommu.h>
> > >+#include <linux/hashtable.h>
> > >
> > >  #include <asm/apic.h>
> > >  #include <asm/perf_event.h>
> > >@@ -928,6 +930,53 @@ static void svm_disable_lbrv(struct vcpu_svm *svm)
> > >  	set_msr_interception(msrpm, MSR_IA32_LASTINTTOIP, 0, 0);
> > >  }
> > >
> > >+/* Note:
> > >+ * This hash table is used to map VM_ID to a struct kvm_arch,
> > >+ * when handling AMD IOMMU GALOG notification to schedule in
> > >+ * a particular vCPU.
> > >+ */
> > >+#define SVM_VM_DATA_HASH_BITS	8
> > >+DECLARE_HASHTABLE(svm_vm_data_hash, SVM_VM_DATA_HASH_BITS);
> > >+static spinlock_t svm_vm_data_hash_lock;
> > >+
> > >+/* Note:
> > >+ * This function is called from IOMMU driver to notify
> > >+ * SVM to schedule in a particular vCPU of a particular VM.
> > >+ */
> > >+static int avic_ga_log_notifier(int vm_id, int vcpu_id)
> > >+{
> > >+	unsigned long flags;
> > >+	struct kvm_arch *ka = NULL;
> > >+	struct kvm_vcpu *vcpu = NULL;
> > >+	struct vcpu_svm *svm = NULL;
> > >+
> > >+	pr_debug("SVM: %s: vm_id=%#x, vcpu_id=%#x\n", __func__, vm_id, vcpu_id);
> > >+
> > >+	spin_lock_irqsave(&svm_vm_data_hash_lock, flags);
> > >+	hash_for_each_possible(svm_vm_data_hash, ka, hnode, vm_id) {
> > >+		struct kvm *kvm = container_of(ka, struct kvm, arch);
> > >+
> > >+		vcpu = kvm_get_vcpu_by_id(kvm, vcpu_id);
> The first result is not neccessarily the correct one.
>
> With more than active 256 VMs, there is a guaranteed collision that
> cannot be disambiguated, so VCPUs in both VMs need to be woken up.
>
> Having a 24 bit vm_id and checking that
>    kvm->*.avic_id & 0xfffff == vm_id
> would help a bit to avoid useless wakeups, but the collision cannot be
> avoided.

True. What if SVM guarantee that the VM_ID won't conflict b/w any two 
active VMs?

Thanks
Suravee.