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

From: Sean Christopherson
Date: Mon Dec 09 2019 - 10:49:17 EST

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@xxxxxxxxx>
> 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.