From: Shivam Kumar <shivam.kumar1@nutanix.com>
To: Sean Christopherson <seanjc@google.com>
Cc: pbonzini@redhat.com, maz@kernel.org, james.morse@arm.com,
borntraeger@linux.ibm.com, david@redhat.com, kvm@vger.kernel.org,
Shaju Abraham <shaju.abraham@nutanix.com>,
Manish Mishra <manish.mishra@nutanix.com>,
Anurag Madnawat <anurag.madnawat@nutanix.com>
Subject: Re: [PATCH v6 2/5] KVM: x86: Dirty quota-based throttling of vcpus
Date: Mon, 10 Oct 2022 00:35:12 +0530 [thread overview]
Message-ID: <c6700c5d-d942-065b-411c-7f4723836054@nutanix.com> (raw)
In-Reply-To: <Y0B+bPDrMdJQVX6p@google.com>
On 08/10/22 1:00 am, Sean Christopherson wrote:
> On Thu, Sep 15, 2022, Shivam Kumar wrote:
>> index c9b49a09e6b5..140a5511ed45 100644
>> --- a/arch/x86/kvm/vmx/vmx.c
>> +++ b/arch/x86/kvm/vmx/vmx.c
>> @@ -5749,6 +5749,9 @@ static int handle_invalid_guest_state(struct kvm_vcpu *vcpu)
>> */
>> if (__xfer_to_guest_mode_work_pending())
>> return 1;
>> +
>> + if (!kvm_vcpu_check_dirty_quota(vcpu))
>
> A dedicated helper is no longer necessary, this can _test_ the event, a la
> KVM_REQ_EVENT above:
>
> if (kvm_test_request(KVM_REQ_DIRTY_QUOTA_EXIT, vcpu))
> return 1;
>
>> + return 0;
>> }
>>
>> return 1;
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 43a6a7efc6ec..8447e70b26f5 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -10379,6 +10379,15 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>> r = 0;
>> goto out;
>> }
>> + if (kvm_check_request(KVM_REQ_DIRTY_QUOTA_EXIT, vcpu)) {
>> + struct kvm_run *run = vcpu->run;
>> +
>
>> + run->exit_reason = KVM_EXIT_DIRTY_QUOTA_EXHAUSTED;
>> + run->dirty_quota_exit.count = vcpu->stat.generic.pages_dirtied;
>> + run->dirty_quota_exit.quota = vcpu->dirty_quota;
>
> As mentioned in patch 1, the code code snippet I suggested is bad. With a request,
> there's no need to snapshot the quota prior to making the request. If userspace
> changes the quota, then using the new quota is perfectly ok since KVM is still
> providing sane data. If userspace lowers the quota, an exit will still ocurr as
> expected. If userspace disables or increases the quota to the point where no exit
> is necessary, then userspace can't expect and exit and won't even be aware that KVM
> temporarily detected an exhausted quota.
>
> And all of this belongs in a common KVM helper. Name isn't pefect, but it aligns
> with kvm_check_request().
>
> #ifdef CONFIG_HAVE_KVM_DIRTY_QUOTA
> static inline bool kvm_check_dirty_quota_request(struct kvm_vcpu *vcpu)
> {
> struct kvm_run *run = vcpu->run;
>
> run->exit_reason = KVM_EXIT_DIRTY_QUOTA_EXHAUSTED;
> run->dirty_quota_exit.count = vcpu->stat.generic.pages_dirtied;
> run->dirty_quota_exit.quota = READ_ONCE(run->dirty_quota);
>
> /*
> * Re-check the quota and exit if and only if the vCPU still exceeds its
> * quota. If userspace increases (or disables entirely) the quota, then
> * no exit is required as KVM is still honoring its ABI, e.g. userspace
> * won't even be aware that KVM temporarily detected an exhausted quota.
> */
> return run->dirty_quota_exit.count >= run->dirty_quota_exit.quota;
> }
> #endif
>
> And then arch usage is simply something like:
>
> if (kvm_check_dirty_quota_request(vcpu)) {
> r = 0;
> goto out;
> }
If we are not even checking for request KVM_REQ_DIRTY_QUOTA_EXIT, what's
the use of kvm_make_request in patch 1?
next prev parent reply other threads:[~2022-10-09 19:05 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-15 10:10 [PATCH v6 0/5] KVM: Dirty quota-based throttling Shivam Kumar
2022-09-15 10:10 ` [PATCH v6 1/5] KVM: Implement dirty quota-based throttling of vcpus Shivam Kumar
2022-09-15 13:21 ` Christian Borntraeger
2022-09-15 14:34 ` Christian Borntraeger
2022-10-07 18:18 ` Sean Christopherson
2022-10-09 18:36 ` Shivam Kumar
2022-10-10 6:12 ` Christian Borntraeger
2022-10-07 19:08 ` Sean Christopherson
2022-10-07 19:20 ` Sean Christopherson
2022-10-09 18:49 ` Shivam Kumar
2022-10-10 16:09 ` Sean Christopherson
2022-10-09 19:30 ` Shivam Kumar
2022-10-10 5:41 ` Shivam Kumar
2022-10-17 5:28 ` Shivam Kumar
2022-10-19 16:01 ` Sean Christopherson
2022-09-15 10:10 ` [PATCH v6 2/5] KVM: x86: Dirty " Shivam Kumar
2022-10-07 19:30 ` Sean Christopherson
2022-10-09 19:05 ` Shivam Kumar [this message]
2022-10-18 17:43 ` Shivam Kumar
2022-10-19 15:42 ` Sean Christopherson
2022-10-09 19:17 ` Shivam Kumar
2022-09-15 10:10 ` [PATCH v6 3/5] KVM: arm64: " Shivam Kumar
2022-09-15 10:10 ` [PATCH v6 4/5] KVM: s390x: " Shivam Kumar
2022-09-15 13:24 ` Christian Borntraeger
2022-09-15 10:10 ` [PATCH v6 5/5] KVM: selftests: Add selftests for dirty quota throttling Shivam Kumar
2022-10-07 18:29 ` Sean Christopherson
2022-10-09 19:26 ` Shivam Kumar
2022-10-10 15:47 ` Sean Christopherson
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