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

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Date:   Mon, 9 Dec 2019 07:49:13 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Ben Hutchings <ben@...adent.org.uk>
Cc:     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 Sun, Dec 08, 2019 at 01:53:15PM +0000, Ben Hutchings wrote:
> 3.16.79-rc1 review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Sean Christopherson <sean.j.christopherson@...el.com>
> 
> commit 16cfacc8085782dab8e365979356ce1ca87fd6cc upstream.

You'll also want to pull in two PAE related fixes (in this order):

  d35b34a9a70e ("kvm: mmu: Don't read PDPTEs when paging is not enabled")
  bf03d4f93347 ("KVM: x86: introduce is_pae_paging")

The "introduce is_pae_paging" has an undocumented bug fix.  IIRC it
manifests as an unexpected #GP on MOV CR3 in 64-bit mode.  Here's the blurb
I added to the backports for 4.x.

  Moving to the common helper also fixes a subtle bug in kvm_set_cr3()
  where it fails to check is_long_mode() and results in KVM incorrectly
  attempting to load PDPTRs for a 64-bit guest.