Re: [PATCH v2 0/8] KVM: x86: nVMX GUEST_CR3 bug fix, and then some...

From: Martin Lucina
Date: Tue Oct 29 2019 - 11:11:32 EST


(Cc:s trimmed)

Hi,

On Monday, 30.09.2019 at 12:42, Reto Buerki wrote:
> On 9/27/19 11:45 PM, Sean Christopherson wrote:
> > *sigh*
> >
> > v2 was shaping up to be a trivial update, until I started working on
> > Vitaly's suggestion to add a helper to test for register availability.
> >
> > The primary purpose of this series is to fix a CR3 corruption in L2
> > reported by Reto Buerki when running with HLT interception disabled in L1.
> > On a nested VM-Enter that puts L2 into HLT, KVM never actually enters L2
> > and instead mimics HLT interception by canceling the nested run and
> > pretending that VM-Enter to L2 completed and then exited on HLT (which
> > KVM intercepted). Because KVM never actually runs L2, KVM skips the
> > pending MMU update for L2 and so leaves a stale value in vmcs02.GUEST_CR3.
> > If the next wake event for L2 triggers a nested VM-Exit, KVM will refresh
> > vmcs12->guest_cr3 from vmcs02.GUEST_CR3 and consume the stale value.
> >
> > Fix the issue by unconditionally writing vmcs02.GUEST_CR3 during nested
> > VM-Enter instead of deferring the update to vmx_set_cr3(), and skip the
> > update of GUEST_CR3 in vmx_set_cr3() when running L2. I.e. make the
> > nested code fully responsible for vmcs02.GUEST_CR3.
> >
> > Patch 02/08 is a minor optimization to skip the GUEST_CR3 update if
> > vmcs01 is already up-to-date.
> >
> > Patches 03 and beyond are Vitaly's fault ;-).
> >
> > Patches 03 and 04 are tangentially related cleanup to vmx_set_rflags()
> > that was discovered when working through the avail/dirty testing code.
> > Ideally they'd be sent as a separate series, but they conflict with the
> > avail/dirty helper changes and are themselves minor and straightforward.
> >
> > Patches 05 and 06 clean up the register caching code so that there is a
> > single enum for all registers which use avail/dirty tracking. While not
> > a true prerequisite for the avail/dirty helpers, the cleanup allows the
> > new helpers to take an 'enum kvm_reg' instead of a less helpful 'int reg'.
> >
> > Patch 07 is the helpers themselves, as suggested by Vitaly.
> >
> > Patch 08 is a truly optional change to ditch decache_cr3() in favor of
> > handling CR3 via cache_reg() like any other avail/dirty register.
> >
> >
> > Note, I collected the Reviewed-by and Tested-by tags for patches 01 and 02
> > even though I inverted the boolean from 'skip_cr3' to 'update_guest_cr3'.
> > Please drop the tags if that constitutes a non-trivial functional change.
> >
> > v2:
> > - Invert skip_cr3 to update_guest_cr3. [Liran]
> > - Reword the changelog and comment to be more explicit in detailing
> > how/when KVM will process a nested VM-Enter without runnin L2. [Liran]
> > - Added Reviewed-by and Tested-by tags.
> > - Add a comment in vmx_set_cr3() to explicitly state that nested
> > VM-Enter is responsible for loading vmcs02.GUEST_CR3. [Jim]
> > - All of the loveliness in patches 03-08. [Vitaly]
> >
> > Sean Christopherson (8):
> > KVM: nVMX: Always write vmcs02.GUEST_CR3 during nested VM-Enter
> > KVM: VMX: Skip GUEST_CR3 VMREAD+VMWRITE if the VMCS is up-to-date
> > KVM: VMX: Consolidate to_vmx() usage in RFLAGS accessors
> > KVM: VMX: Optimize vmx_set_rflags() for unrestricted guest
> > KVM: x86: Add WARNs to detect out-of-bounds register indices
> > KVM: x86: Fold 'enum kvm_ex_reg' definitions into 'enum kvm_reg'
> > KVM: x86: Add helpers to test/mark reg availability and dirtiness
> > KVM: x86: Fold decache_cr3() into cache_reg()
> >
> > arch/x86/include/asm/kvm_host.h | 5 +-
> > arch/x86/kvm/kvm_cache_regs.h | 67 +++++++++++++++++------
> > arch/x86/kvm/svm.c | 5 --
> > arch/x86/kvm/vmx/nested.c | 14 ++++-
> > arch/x86/kvm/vmx/vmx.c | 94 ++++++++++++++++++---------------
> > arch/x86/kvm/x86.c | 13 ++---
> > arch/x86/kvm/x86.h | 6 +--
> > 7 files changed, 123 insertions(+), 81 deletions(-)
>
> Series:
> Tested-by: Reto Buerki <reet@xxxxxxxxxxx>

Any chance of this series making it into 5.4? Unless I'm looking in the
wrong place, I don't see the changes in either kvm.git or Linus' tree.

Thanks,

Martin