linux-kernel - Re: [PART2 PATCH v4 10/11] svm: Introduce AMD IOMMU avic_ga_log

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Date:	Thu, 14 Jul 2016 16:43:47 +0700
From:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
To:	Radim Krčmář <rkrcmar@...hat.com>
CC:	<joro@...tes.org>, <pbonzini@...hat.com>,
	<alex.williamson@...hat.com>, <kvm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <sherry.hurwitz@....com>
Subject: Re: [PART2 PATCH v4 10/11] svm: Introduce AMD IOMMU
 avic_ga_log_notifier

Hi Radim,

On 7/13/16 21:29, Radim Krčmář wrote:
> 2016-07-13 08:20-0500, Suravee Suthikulpanit:
>> >From: Suravee Suthikulpanit<Suravee.Suthikulpanit@....com>
>> >
>> >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@....com>
>> >---
>> >  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.