lkml.org 
[lkml]   [2022]   [May]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH v2 08/12] KVM: SVM: Update AVIC settings when changing APIC mode
From
Maxim, Sean

On 4/18/22 7:55 PM, Maxim Levitsky wrote:
> On Tue, 2022-04-12 at 06:58 -0500, Suravee Suthikulpanit wrote:
>> When APIC mode is updated (e.g. disabled, xAPIC, or x2APIC),
>> KVM needs to call kvm_vcpu_update_apicv() to update AVIC settings
>> accordingly.
>>
>> Signed-off-by: Suravee Suthikulpanit<suravee.suthikulpanit@amd.com>
>> ---
>> arch/x86/kvm/svm/avic.c | 15 +++++++++++++++
>> arch/x86/kvm/svm/svm.c | 1 +
>> 2 files changed, 16 insertions(+)
>>
>> diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
>> index 22ee1098e2a5..01392b8364f4 100644
>> --- a/arch/x86/kvm/svm/avic.c
>> +++ b/arch/x86/kvm/svm/avic.c
>> @@ -616,6 +616,21 @@ void avic_apicv_post_state_restore(struct kvm_vcpu *vcpu)
>> avic_handle_ldr_update(vcpu);
>> }
>>
>> +void avic_set_virtual_apic_mode(struct kvm_vcpu *vcpu)
>> +{
>> + struct vcpu_svm *svm = to_svm(vcpu);
>> +
>> + if (!lapic_in_kernel(vcpu) || (avic_mode == AVIC_MODE_NONE))
>> + return;
>> +
>> + if (kvm_get_apic_mode(vcpu) == LAPIC_MODE_INVALID) {
>> + WARN_ONCE(true, "Invalid local APIC state (vcpu_id=%d)", vcpu->vcpu_id);
>> + return;
>> + }
>> +
>> + kvm_vcpu_update_apicv(&svm->vcpu);
> I think it makes sense to call avic_refresh_apicv_exec_ctrl directly here.
>
> I am not sure that kvm_vcpu_update_apicv will even call it
> because it has an optimization of doing nothing when inhibition status
> didn't change.
>
>
> Another semi-related note:
>
> the current way the x2avic msrs are configured creates slight performance
> problem for nesting:
>
> The problem is that when entering a nested guest, AVIC on the current vCPU
> is inhibited, but this is done only so that this vCPU*peers* don't
> try to use AVIC to send IPIs to it, so there is no need to update vmcb01
> msr interception bitmap, and vmcb02 should have all these msrs intercepted always.
> Same with returning to host.
>
> It also should be checked that during nested entry, at least vmcb01 msr bitmap
> is updated - TL;DR - please check that x2avic works when there is a nested guest running.

In the kvm/queue branch, I found a regression on nested SVM guest, where L2 guest cannot
launch. The bad commit is:

commit a4cfff3f0f8c07f1f7873a82bdeb3995807dac8c (bisect)
Merge: 42dcbe7d8bac 8d5678a76689
Author: Paolo Bonzini <pbonzini@redhat.com>
Date: Fri Apr 8 12:43:40 2022 -0400

Merge branch 'kvm-older-features' into HEAD

Merge branch for features that did not make it into 5.18:

* New ioctls to get/set TSC frequency for a whole VM

* Allow userspace to opt out of hypercall patching

Nested virtualization improvements for AMD:

* Support for "nested nested" optimizations (nested vVMLOAD/VMSAVE,
nested vGIF)

* Allow AVIC to co-exist with a nested guest running

* Fixes for LBR virtualizations when a nested guest is running,
and nested LBR virtualization support

* PAUSE filtering for nested hypervisors

Guest support:

* Decoupling of vcpu_is_preempted from PV spinlocks

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

I am still working on the bisect into the merge commits.

Regards,
Suravee

\
 
 \ /
  Last update: 2022-05-02 16:08    [W:0.122 / U:1.820 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site