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From: Liran Alon <liran.alon@oracle.com>
To: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: qemu-devel@nongnu.org, pbonzini@redhat.com, mtosatti@redhat.com,
	rth@twiddle.net, ehabkost@redhat.com, kvm@vger.kernel.org,
	jmattson@google.com, maran.wilson@oracle.com,
	Nikita Leshenko <nikita.leshchenko@oracle.com>
Subject: Re: [QEMU PATCH v3 8/9] KVM: i386: Add support for KVM_CAP_EXCEPTION_PAYLOAD
Date: Tue, 18 Jun 2019 18:45:43 +0300
Message-ID: <350BC330-8877-4B93-A8B3-0C001AEDD879@oracle.com> (raw)
In-Reply-To: <20190618090752.GD2850@work-vm>



> On 18 Jun 2019, at 12:07, Dr. David Alan Gilbert <dgilbert@redhat.com> wrote:
> 
> * Liran Alon (liran.alon@oracle.com) wrote:
>> Kernel commit c4f55198c7c2 ("kvm: x86: Introduce KVM_CAP_EXCEPTION_PAYLOAD")
>> introduced a new KVM capability which allows userspace to correctly
>> distinguish between pending and injected exceptions.
>> 
>> This distinguish is important in case of nested virtualization scenarios
>> because a L2 pending exception can still be intercepted by the L1 hypervisor
>> while a L2 injected exception cannot.
>> 
>> Furthermore, when an exception is attempted to be injected by QEMU,
>> QEMU should specify the exception payload (CR2 in case of #PF or
>> DR6 in case of #DB) instead of having the payload already delivered in
>> the respective vCPU register. Because in case exception is injected to
>> L2 guest and is intercepted by L1 hypervisor, then payload needs to be
>> reported to L1 intercept (VMExit handler) while still preserving
>> respective vCPU register unchanged.
>> 
>> This commit adds support for QEMU to properly utilise this new KVM
>> capability (KVM_CAP_EXCEPTION_PAYLOAD).
> 
> Does this kvm capability become a requirement for the nested migration
> then? If so, is it wired into the blockers?
> 
> Dave
> 

That’s a very good point.
Yes this capability is required in order to correctly migrate VMs running nested hypervisors.
I agree that I should add a migration blocker for nested in case it isn’t present.
Nice catch.

-Liran



  reply index

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-17 17:56 [QEMU PATCH v3 0/9]: KVM: i386: Add support for save and restore of nested state Liran Alon
2019-06-17 17:56 ` [QEMU PATCH v3 1/9] KVM: Introduce kvm_arch_destroy_vcpu() Liran Alon
2019-06-18 22:15   ` [Qemu-devel] " Maran Wilson
2019-06-17 17:56 ` [QEMU PATCH v3 2/9] KVM: i386: Use symbolic constant for #DB/#BP exception constants Liran Alon
2019-06-17 17:56 ` [QEMU PATCH v3 3/9] KVM: i386: Re-inject #DB to guest with updated DR6 Liran Alon
2019-06-17 17:56 ` [QEMU PATCH v3 4/9] KVM: i386: Block migration for vCPUs exposed with nested virtualization Liran Alon
2019-06-18  8:44   ` Dr. David Alan Gilbert
2019-06-18 22:16   ` [Qemu-devel] " Maran Wilson
2019-06-17 17:56 ` [QEMU PATCH v3 5/9] linux-headers: i386: Modify struct kvm_nested_state to have explicit fields for data Liran Alon
2019-06-18 22:16   ` [Qemu-devel] " Maran Wilson
2019-06-17 17:56 ` [QEMU PATCH v3 6/9] vmstate: Add support for kernel integer types Liran Alon
2019-06-18  8:55   ` Dr. David Alan Gilbert
2019-06-18 15:36     ` Liran Alon
2019-06-18 15:42       ` Dr. David Alan Gilbert
2019-06-18 16:44         ` Paolo Bonzini
2019-06-17 17:56 ` [QEMU PATCH v3 7/9] KVM: i386: Add support for save and restore nested state Liran Alon
2019-06-18  9:03   ` Dr. David Alan Gilbert
2019-06-18 15:40     ` Liran Alon
2019-06-18 15:48       ` Dr. David Alan Gilbert
2019-06-18 15:50         ` Liran Alon
2019-06-18 16:16         ` Paolo Bonzini
2019-06-18 22:16   ` [Qemu-devel] " Maran Wilson
2019-06-17 17:56 ` [QEMU PATCH v3 8/9] KVM: i386: Add support for KVM_CAP_EXCEPTION_PAYLOAD Liran Alon
2019-06-18  9:07   ` Dr. David Alan Gilbert
2019-06-18 15:45     ` Liran Alon [this message]
2019-06-17 17:56 ` [QEMU PATCH v3 9/9] KVM: i386: Remove VMX migration blocker Liran Alon
2019-06-18 22:17   ` [Qemu-devel] " Maran Wilson

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