linux-kernel - Re: [PATCH] KVM: x86: Load DR6 with guest value only before entering .vcpu

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Message-ID: <Z6_ai1HdLWiTJ2Pf@google.com>
Date: Fri, 14 Feb 2025 16:06:35 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	John Stultz <jstultz@...gle.com>, Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH] KVM: x86: Load DR6 with guest value only before entering
 .vcpu_run() loop

On Fri, Feb 14, 2025, Paolo Bonzini wrote:
> Queued, thanks.

Drat, I was too slow today.  I applied and pushed this to "kvm-x86 fixes" and
linux-next (as of yesterday), along with a few other things, I just haven't sent
out the "thanks" yet (got sidetracked).

If you want to grab those, here's a semi-impromptu pull request.  Otherwise I'll
just drop this particular commit.

--

The following changes since commit a64dcfb451e254085a7daee5fe51bf22959d52d3:

  Linux 6.14-rc2 (2025-02-09 12:45:03 -0800)

are available in the Git repository at:

  https://github.com/kvm-x86/linux.git tags/kvm-x86-fixes-6.14-rcN

for you to fetch changes up to c2fee09fc167c74a64adb08656cb993ea475197e:

  KVM: x86: Load DR6 with guest value only before entering .vcpu_run() loop (2025-02-12 08:59:38 -0800)

----------------------------------------------------------------
KVM fixes for 6.14 part 1

 - Reject Hyper-V SEND_IPI hypercalls if the local APIC isn't being emulated
   by KVM to fix a NULL pointer dereference.

 - Enter guest mode (L2) from KVM's perspective before initializing the vCPU's
   nested NPT MMU so that the MMU is properly tagged for L2, not L1.

 - Load the guest's DR6 outside of the innermost .vcpu_run() loop, as the
   guest's value may be stale if a VM-Exit is handled in the fastpath.

----------------------------------------------------------------
Sean Christopherson (6):
      KVM: x86: Reject Hyper-V's SEND_IPI hypercalls if local APIC isn't in-kernel
      KVM: selftests: Mark test_hv_cpuid_e2big() static in Hyper-V CPUID test
      KVM: selftests: Manage CPUID array in Hyper-V CPUID test's core helper
      KVM: selftests: Add CPUID tests for Hyper-V features that need in-kernel APIC
      KVM: nSVM: Enter guest mode before initializing nested NPT MMU
      KVM: x86: Load DR6 with guest value only before entering .vcpu_run() loop

 arch/x86/include/asm/kvm-x86-ops.h             |  1 +
 arch/x86/include/asm/kvm_host.h                |  1 +
 arch/x86/kvm/hyperv.c                          |  6 +++++-
 arch/x86/kvm/mmu/mmu.c                         |  2 +-
 arch/x86/kvm/svm/nested.c                      | 10 +++++-----
 arch/x86/kvm/svm/svm.c                         | 13 ++++++-------
 arch/x86/kvm/vmx/main.c                        |  1 +
 arch/x86/kvm/vmx/vmx.c                         | 10 ++++++----
 arch/x86/kvm/vmx/x86_ops.h                     |  1 +
 arch/x86/kvm/x86.c                             |  3 +++
 tools/testing/selftests/kvm/x86/hyperv_cpuid.c | 47 ++++++++++++++++++++++++++++++++---------------
 11 files changed, 62 insertions(+), 33 deletions(-)