linux-kernel - Re: [PATCH 4.19 009/191] KVM: nVMX: Use correct root level for nested EPT shadow page tables

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Date:   Fri, 21 Feb 2020 11:29:49 +0100
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 009/191] KVM: nVMX: Use correct root level for
 nested EPT shadow page tables

Hi!

> Hardcode the EPT page-walk level for L2 to be 4 levels, as KVM's MMU
> currently also hardcodes the page walk level for nested EPT to be 4
> levels.  The L2 guest is all but guaranteed to soft hang on its first
> instruction when L1 is using EPT, as KVM will construct 4-level page
> tables and then tell hardware to use 5-level page tables.

I don't get it. 7/191 reverts the patch, then 9/191 reverts the
revert. Can we simply drop both 7 and 9, for exactly the same result?

(Patch 8 is a unused file, so it does not change the picture).

Best regards,
								Pavel

> +++ b/arch/x86/kvm/vmx.c
> @@ -5302,6 +5302,9 @@ static void vmx_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
>  
>  static int get_ept_level(struct kvm_vcpu *vcpu)
>  {
> +	/* Nested EPT currently only supports 4-level walks. */
> +	if (is_guest_mode(vcpu) && nested_cpu_has_ept(get_vmcs12(vcpu)))
> +		return 4;
>  	if (cpu_has_vmx_ept_5levels() && (cpuid_maxphyaddr(vcpu) > 48))
>  		return 5;
>  	return 4;
> -- 
> 2.20.1
> 
> 

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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