On Thu, Jan 25, 2018 at 01:25:18AM -0800, Liran Alon wrote:

----- Alexander.Levin@microsoft.com wrote:

...

From: Liran Alon liran.alon@oracle.com

[ Upstream commit ac9b305caa0df6f5b75d294e4b86c1027648991e ]

When running L2, #UD should be intercepted by L1 or just forwarded directly to L2. It should not reach L0 x86 emulator. Therefore, set intercept for #UD only based on L1 exception-bitmap.

Also add WARN_ON_ONCE() on L0 #UD intercept handlers to make sure it is never reached while running L2.

This improves commit ae1f57670703 ("KVM: nVMX: Do not emulate #UD while in guest mode") by removing an unnecessary exit from L2 to L0 on #UD when L1 doesn't intercept it.

In addition, SVM L0 #UD intercept handler doesn't handle correctly the case it is raised from L2. In this case, it should forward the #UD to guest instead of x86 emulator. As done in VMX #UD intercept handler. This commit fixes this issue as-well.

Signed-off-by: Liran Alon liran.alon@oracle.com Reviewed-by: Nikita Leshenko nikita.leshchenko@oracle.com Reviewed-by: Konrad Rzeszutek Wilk konrad.wilk@oracle.com Signed-off-by: Konrad Rzeszutek Wilk konrad.wilk@oracle.com Reviewed-by: Paolo Bonzini pbonzini@redhat.com Reviewed-by: Wanpeng Li wanpeng.li@hotmail.com Signed-off-by: Radim Krčmář rkrcmar@redhat.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com

---

arch/x86/kvm/svm.c | 9 ++++++++- arch/x86/kvm/vmx.c | 9 ++++----- 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c index 6a8284f72328..c8be4e6d365b 100644 --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -362,6 +362,7 @@ static void recalc_intercepts(struct vcpu_svm *svm) { struct vmcb_control_area *c, *h; struct nested_state *g;

• u32 h_intercept_exceptions;

mark_dirty(svm->vmcb, VMCB_INTERCEPTS); @@ -372,9 +373,14 @@ static void recalc_intercepts(struct vcpu_svm *svm) h = &svm->nested.hsave->control; g = &svm->nested;

• /* No need to intercept #UD if L1 doesn't intercept it */
• h_intercept_exceptions =

• h->intercept_exceptions & ~(1U << UD_VECTOR);
  

• c->intercept_cr = h->intercept_cr | g->intercept_cr; c->intercept_dr = h->intercept_dr | g->intercept_dr;

• c->intercept_exceptions = h->intercept_exceptions |

g->intercept_exceptions;

• c->intercept_exceptions =

• h_intercept_exceptions | g->intercept_exceptions;
  

  c->intercept = h->intercept | g->intercept;

} @@ -2189,6 +2195,7 @@ static int ud_interception(struct vcpu_svm *svm) { int er;

• WARN_ON_ONCE(is_guest_mode(&svm->vcpu)); er = emulate_instruction(&svm->vcpu, EMULTYPE_TRAP_UD); if (er == EMULATE_USER_EXIT) return 0;

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index ef16cf0f7cfd..36628ed362d8 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -1891,7 +1891,7 @@ static void update_exception_bitmap(struct kvm_vcpu *vcpu) { u32 eb;

• eb = (1u << PF_VECTOR) | (1u << UD_VECTOR) | (1u << MC_VECTOR) |

• eb = (1u << PF_VECTOR) | (1u << MC_VECTOR) | (1u << DB_VECTOR) | (1u << AC_VECTOR); if ((vcpu->guest_debug & (KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_SW_BP)) ==

@@ -1909,6 +1909,8 @@ static void update_exception_bitmap(struct kvm_vcpu *vcpu) */ if (is_guest_mode(vcpu)) eb |= get_vmcs12(vcpu)->exception_bitmap;

• else

• eb |= 1u << UD_VECTOR;
  

vmcs_write32(EXCEPTION_BITMAP, eb); } @@ -5919,10 +5921,7 @@ static int handle_exception(struct kvm_vcpu *vcpu) return 1; /* already handled by vmx_vcpu_run() */ if (is_invalid_opcode(intr_info)) {

• if (is_guest_mode(vcpu)) {
  

• 	kvm_queue_exception(vcpu, UD_VECTOR);
  

• 	return 1;
  

• }
  

• WARN_ON_ONCE(is_guest_mode(vcpu));
  

  er = emulate_instruction(vcpu, EMULTYPE_TRAP_UD); if (er == EMULATE_USER_EXIT) return 0;

-- 2.11.0

Just wanted stable maintainers to note that Jim, Paolo & myself decided eventually to revert this commit along with commit ae1f57670703 on upstream KVM. However, it is true that this commit makes commit ae1f57670703 more complete. Therefore we have 2 options here:

1. Apply this backport and sometime in the future also apply the reverts of both these commits with Paolo's commit which reverts them.

Being "bug compatible" is good, I like that option :)

When is the revert patch going to hit Linus's tree? During the 4.16-rc1 merge window?

thanks,

greg k-h