Re: [PATCH] KVM: mmu: Fix SPTE encoding of MMIO generation upper half

[Greg KH <greg@kroah.com>]

On Thu, Dec 17, 2020 at 02:46:13PM +0100, Maciej S. Szmigiero wrote:
> From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
> 
> Commit cae7ed3c2cb0 ("KVM: x86: Refactor the MMIO SPTE generation handling")
> cleaned up the computation of MMIO generation SPTE masks, however it
> introduced a bug how the upper part was encoded:
> SPTE bits 52-61 were supposed to contain bits 10-19 of the current
> generation number, however a missing shift encoded bits 1-10 there instead
> (mostly duplicating the lower part of the encoded generation number that
> then consisted of bits 1-9).
> 
> In the meantime, the upper part was shrunk by one bit and moved by
> subsequent commits to become an upper half of the encoded generation number
> (bits 9-17 of bits 0-17 encoded in a SPTE).
> 
> In addition to the above, commit 56871d444bc4 ("KVM: x86: fix overlap between SPTE_MMIO_MASK and generation")
> has changed the SPTE bit range assigned to encode the generation number and
> the total number of bits encoded but did not update them in the comment
> attached to their defines, nor in the KVM MMU doc.
> Let's do it here, too, since it is too trivial thing to warrant a separate
> commit.
> 
> This is a backport of the upstream commit for 5.4.x stable series, which
> has KVM docs still in a raw text format and the x86 KVM MMU isn't yet split
> into separate files under "mmu" directory.
> Other than that, it's a straightforward port.
> 
> Fixes: cae7ed3c2cb0 ("KVM: x86: Refactor the MMIO SPTE generation handling")
> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> [Reorganize macros so that everything is computed from the bit ranges. - Paolo]
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> (cherry picked from commit 34c0f6f2695a2db81e09a3ab7bdb2853f45d4d3d)
> Cc: stable@vger.kernel.org # 5.4.x
> ---
>  Documentation/virt/kvm/mmu.txt |  2 +-
>  arch/x86/kvm/mmu.c             | 29 ++++++++++++++++++++---------
>  2 files changed, 21 insertions(+), 10 deletions(-)

Thanks for both backports!

greg k-h