linux-kernel - Re: [PATCH v1 3/4] KVM: MMU: Add 5 level EPT & Shadow page table support.

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Date:   Mon, 14 Aug 2017 09:31:54 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Yu Zhang <yu.c.zhang@...ux.intel.com>, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, rkrcmar@...hat.com,
        tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        xiaoguangrong@...cent.com, joro@...tes.org
Subject: Re: [PATCH v1 3/4] KVM: MMU: Add 5 level EPT & Shadow page table
 support.

On 12/08/2017 15:35, Yu Zhang wrote:
>  struct rsvd_bits_validate {
> -	u64 rsvd_bits_mask[2][4];
> +	u64 rsvd_bits_mask[2][5];
>  	u64 bad_mt_xwr;
>  };


Can you change this 4 to PT64_ROOT_MAX_LEVEL in patch 2?

> -	if (vcpu->arch.mmu.shadow_root_level == PT64_ROOT_4LEVEL &&
> -	    (vcpu->arch.mmu.root_level == PT64_ROOT_4LEVEL ||
> -	     vcpu->arch.mmu.direct_map)) {
> +	if (vcpu->arch.mmu.root_level >= PT64_ROOT_4LEVEL ||
> +	    vcpu->arch.mmu.direct_map) {
>  		hpa_t root = vcpu->arch.mmu.root_hpa;

You should keep the check on shadow_root_level (changing it to >= of
course), otherwise you break the case where EPT is disabled, paging is
disabled (so vcpu->arch.mmu.direct_map is true) and the host kernel is
32-bit.  In that case shadow pages use PAE format, and entering this
branch is incorrect.

> @@ -4444,7 +4457,7 @@ void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, bool execonly,
>  
>  	MMU_WARN_ON(VALID_PAGE(context->root_hpa));
>  
> -	context->shadow_root_level = kvm_x86_ops->get_tdp_level();
> +	context->shadow_root_level = kvm_x86_ops->get_tdp_level(vcpu);
>  
>  	context->nx = true;
>  	context->ept_ad = accessed_dirty;

Below, there is:

        context->root_level = context->shadow_root_level;

this should be forced to PT64_ROOT_4LEVEL until there is support for
nested EPT 5-level page tables.

Thanks,

Paolo