linux-kernel - Re: [PATCH 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor

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Date:   Thu, 3 Aug 2017 13:39:30 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Bandan Das <bsd@...hat.com>, kvm@...r.kernel.org
Cc:     pbonzini@...hat.com, rkrcmar@...hat.com, jmattson@...gle.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] KVM: nVMX: Emulate EPTP switching for the L1
 hypervisor


>  
> +static bool valid_ept_address(struct kvm_vcpu *vcpu, u64 address)
> +{
> +	struct vcpu_vmx *vmx = to_vmx(vcpu);
> +	u64 mask = address & 0x7;
> +	int maxphyaddr = cpuid_maxphyaddr(vcpu);
> +
> +	/* Check for memory type validity */
> +	switch (mask) {
> +	case 0:
> +		if (!(vmx->nested.nested_vmx_ept_caps & VMX_EPTP_UC_BIT))
> +			return false;
> +		break;
> +	case 6:
> +		if (!(vmx->nested.nested_vmx_ept_caps & VMX_EPTP_WB_BIT))
> +			return false;
> +		break;
> +	default:
> +		return false;
> +	}
> +
> +	/* Bits 5:3 must be 3 */
> +	if (((address >> VMX_EPT_GAW_EPTP_SHIFT) & 0x7) != VMX_EPT_DEFAULT_GAW)
> +		return false;
> +
> +	/* Reserved bits should not be set */
> +	if (address >> maxphyaddr || ((address >> 7) & 0x1f))
> +		return false;
> +
> +	/* AD, if set, should be supported */
> +	if ((address & VMX_EPT_AD_ENABLE_BIT)) {
> +		if (!enable_ept_ad_bits)
> +			return false;

In theory (I guess) we would have to check here if
(vmx->nested.nested_vmx_ept_caps & VMX_EPT_AD_BIT)

But I am no expert on this.

> +	}
> +
> +	return true;
> +}
> +
> +static int nested_vmx_eptp_switching(struct kvm_vcpu *vcpu,
> +				     struct vmcs12 *vmcs12)
> +{
> +	u32 index = vcpu->arch.regs[VCPU_REGS_RCX];
> +	u64 *l1_eptp_list, address;
> +	struct page *page;
> +	bool accessed_dirty;
> +	struct kvm_mmu *mmu = vcpu->arch.walk_mmu;
> +
> +	if (!nested_cpu_has_eptp_switching(vmcs12) ||
> +	    !nested_cpu_has_ept(vmcs12))
> +		return 1;
> +
> +	if (index >= VMFUNC_EPTP_ENTRIES)
> +		return 1;
> +
> +	page = nested_get_page(vcpu, vmcs12->eptp_list_address);
> +	if (!page)
> +		return 1;
> +
> +	l1_eptp_list = kmap(page);
> +	address = l1_eptp_list[index];
> +	accessed_dirty = !!(address & VMX_EPT_AD_ENABLE_BIT);

Minor nit: Can't you directly do

kunmap(page);
nested_release_page_clean(page);

at this point?

We can fix this up later.

We could even later factor this out into sth. like "nested_vmx_read_guest".

-- 

Thanks,

David