linux-kernel - Re: [PATCH] KVM: nVMX: nested TPR shadow/threshold emulation

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Message-ID: <53D90D5A.3060404@redhat.com>
Date:	Wed, 30 Jul 2014 17:20:58 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Wanpeng Li <wanpeng.li@...ux.intel.com>,
	Jan Kiszka <jan.kiszka@...mens.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	Gleb Natapov <gleb@...nel.org>, Bandan Das <bsd@...hat.com>,
	Zhang Yang <yang.z.zhang@...el.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: nVMX: nested TPR shadow/threshold emulation

Il 30/07/2014 14:04, Wanpeng Li ha scritto:
> @@ -7962,14 +7965,14 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
>  		if (!vmx->rdtscp_enabled)
>  			exec_control &= ~SECONDARY_EXEC_RDTSCP;
>  		/* Take the following fields only from vmcs12 */
> -		exec_control &= ~(SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES |
> -				  SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY |
> +		exec_control &= ~(SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY |
>                                    SECONDARY_EXEC_APIC_REGISTER_VIRT);

This change is wrong.  You don't have to take L0's "virtualize APIC
accesses" setting into account, because while running L2 you cannot
modify L1's CR8 (only the virtual nested one).

> +
> +			virtual_apic_page = nested_get_page(vcpu,
> +						vmcs12->virtual_apic_page_addr);
> +			if (vmcs_read64(VIRTUAL_APIC_PAGE_ADDR) !=
> +					page_to_phys(virtual_apic_page))
> +				vmcs_write64(VIRTUAL_APIC_PAGE_ADDR,
> +					page_to_phys(virtual_apic_page));
> +			nested_release_page(virtual_apic_page);
> +

You cannot release this page here.  You need to the exactly the same
thing that is done for apic_access_page.

One thing:

> +	if (nested_cpu_has(vmcs12, CPU_BASED_TPR_SHADOW))
> +		vmcs_write32(TPR_THRESHOLD, vmcs12->tpr_threshold);

I think you can just do this write unconditionally, since most
hypervisors will enable this.  Also, you probably can add the tpr
threshold field to the read-write fields for shadow VMCS.

Paolo
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