linux-kernel - Re: [PATCH v2] KVM: SVM: Disable AVIC before setting V

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Date:   Thu, 7 May 2020 10:27:00 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     joro@...tes.org, jon.grimm@....com, mlevitsk@...hat.com
Subject: Re: [PATCH v2] KVM: SVM: Disable AVIC before setting V_IRQ

On 07/05/20 04:35, Suravee Suthikulpanit wrote:
> The commit 64b5bd270426 ("KVM: nSVM: ignore L1 interrupt window
> while running L2 with V_INTR_MASKING=1") introduced a WARN_ON,
> which checks if AVIC is enabled when trying to set V_IRQ
> in the VMCB for enabling irq window.
> 
> The following warning is triggered because the requesting vcpu
> (to deactivate AVIC) does not get to process APICv update request
> for itself until the next #vmexit.
> 
> WARNING: CPU: 0 PID: 118232 at arch/x86/kvm/svm/svm.c:1372 enable_irq_window+0x6a/0xa0 [kvm_amd]
>  RIP: 0010:enable_irq_window+0x6a/0xa0 [kvm_amd]
>  Call Trace:
>   kvm_arch_vcpu_ioctl_run+0x6e3/0x1b50 [kvm]
>   ? kvm_vm_ioctl_irq_line+0x27/0x40 [kvm]
>   ? _copy_to_user+0x26/0x30
>   ? kvm_vm_ioctl+0xb3e/0xd90 [kvm]
>   ? set_next_entity+0x78/0xc0
>   kvm_vcpu_ioctl+0x236/0x610 [kvm]
>   ksys_ioctl+0x8a/0xc0
>   __x64_sys_ioctl+0x1a/0x20
>   do_syscall_64+0x58/0x210
>   entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Fixes by sending APICV update request to all other vcpus, and
> immediately update APIC for itself.
> 
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
> Link: https://lkml.org/lkml/2020/5/2/167
> Fixes: 64b5bd270426 ("KVM: nSVM: ignore L1 interrupt window while running L2 with V_INTR_MASKING=1")
> ---
>  arch/x86/kvm/x86.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index df473f9..69a01ea 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8085,6 +8085,7 @@ void kvm_vcpu_update_apicv(struct kvm_vcpu *vcpu)
>   */
>  void kvm_request_apicv_update(struct kvm *kvm, bool activate, ulong bit)
>  {
> +	struct kvm_vcpu *except;
>  	unsigned long old, new, expected;
>  
>  	if (!kvm_x86_ops.check_apicv_inhibit_reasons ||
> @@ -8110,7 +8111,17 @@ void kvm_request_apicv_update(struct kvm *kvm, bool activate, ulong bit)
>  	trace_kvm_apicv_update_request(activate, bit);
>  	if (kvm_x86_ops.pre_update_apicv_exec_ctrl)
>  		kvm_x86_ops.pre_update_apicv_exec_ctrl(kvm, activate);
> -	kvm_make_all_cpus_request(kvm, KVM_REQ_APICV_UPDATE);
> +
> +	/*
> +	 * Sending request to update APICV for all other vcpus,
> +	 * while update the calling vcpu immediately instead of
> +	 * waiting for another #VMEXIT to handle the request.
> +	 */
> +	except = kvm_get_running_vcpu();
> +	kvm_make_all_cpus_request_except(kvm, KVM_REQ_APICV_UPDATE,
> +					 except);
> +	if (except)
> +		kvm_vcpu_update_apicv(except);
>  }
>  EXPORT_SYMBOL_GPL(kvm_request_apicv_update);
>  
> 

Queued, thanks.

Paolo