On Wed, May 25, 2022, Venkatesh Srinivas wrote: > From: Marc Orr <marcorr@xxxxxxxxxx> > > From: Venkatesh Srinivas <venkateshs@xxxxxxxxxxxx> Heh, something is wonky in your setup, only Marc should get an explicit From: > The upper bytes of any x2APIC register are reserved. Inject a #GP > into the guest if any of these reserved bits are set. > > Signed-off-by: Marc Orr <marcorr@xxxxxxxxxx> > Signed-off-by: Venkatesh Srinivas <venkateshs@xxxxxxxxxxxx> > --- > arch/x86/kvm/lapic.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index 6f8522e8c492..617e4936c5cc 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -2907,6 +2907,8 @@ int kvm_x2apic_msr_write(struct kvm_vcpu *vcpu, u32 msr, u64 data) > > if (!lapic_in_kernel(vcpu) || !apic_x2apic_mode(apic)) > return 1; > + else if (data >> 32) > + return 1; This is incorrect, ICR is a 64-bit value. Marc's changelog for the internal patch was wrong, although the code was correct. The correct upstream change is: diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 39b805666a18..54d0f350acdf 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -2892,6 +2892,9 @@ static int kvm_lapic_msr_write(struct kvm_lapic *apic, u32 reg, u64 data) if (reg == APIC_ICR) return kvm_x2apic_icr_write(apic, data); + if (data >> 32) + return 1; + return kvm_lapic_reg_write(apic, reg, (u32)data); } As penance for not testing, can you write a KUT testcase to hit all the registers? You could use e.g. SIPI to test that a 64-bit ICR value is _not_ rejected. One thought would be to base your testcase on top of similar changes to msr.c to blast all of the MCE MSRs, e.g. add a path/helper to enable x2APIC and iterate over all registers. [*] https://lore.kernel.org/all/20220512233045.4125471-1-seanjc@xxxxxxxxxx