linux-kernel - Re: [PATCH 3.16 31/72] KVM: x86: Manually calculate reserved bits when loading PDPTRS

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Date:   Tue, 10 Dec 2019 08:27:31 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Ben Hutchings <ben@...adent.org.uk>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        Nadav Amit <nadav.amit@...il.com>,
        Doug Reiland <doug.reiland@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Peter Xu <peterx@...hat.com>
Subject: Re: [PATCH 3.16 31/72] KVM: x86: Manually calculate reserved bits
 when loading PDPTRS

On Tue, Dec 10, 2019 at 04:16:44PM +0000, Ben Hutchings wrote:
> The 3.16, 4.4, and 4.9 branches have slightly different conditions in
> kvm_set_cr3():
> 
> 	if (is_long_mode(vcpu)) {
> 		if (cr3 & CR3_L_MODE_RESERVED_BITS)
> 			return 1;
> 	} else if (is_pae(vcpu) && is_paging(vcpu) &&
> 		   !load_pdptrs(vcpu, vcpu->arch.walk_mmu, cr3))
> 		return 1;
> 
> So load_pdptrs() already won't be called if is_long_mode() returns
> true, and this fix shouldn't be needed.

Argh, glad you double checked!  I looked at 3.16.y, but apparently I didn't
actually read the code...