The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a7c42bb6da6b1b54b2e7bd567636d72d87b10a79 Mon Sep 17 00:00:00 2001

From: Vitaly Kuznetsov vkuznets@redhat.com Date: Tue, 16 Oct 2018 18:50:06 +0200 Subject: [PATCH] x86/kvm/lapic: preserve gfn_to_hva_cache len on cache reinit

vcpu->arch.pv_eoi is accessible through both HV_X64_MSR_VP_ASSIST_PAGE and MSR_KVM_PV_EOI_EN so on migration userspace may try to restore them in any order. Values match, however, kvm_lapic_enable_pv_eoi() uses different length: for Hyper-V case it's the whole struct hv_vp_assist_page, for KVM native case it is 8. In case we restore KVM-native MSR last cache will be reinitialized with len=8 so trying to access VP assist page beyond 8 bytes with kvm_read_guest_cached() will fail.

Check if we re-initializing cache for the same address and preserve length in case it was greater.

Signed-off-by: Vitaly Kuznetsov vkuznets@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Paolo Bonzini pbonzini@redhat.com

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 79358fd6a71c..3cd227ff807f 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -2647,14 +2647,22 @@ int kvm_hv_vapic_msr_read(struct kvm_vcpu *vcpu, u32 reg, u64 *data) int kvm_lapic_enable_pv_eoi(struct kvm_vcpu *vcpu, u64 data, unsigned long len) { u64 addr = data & ~KVM_MSR_ENABLED; + struct gfn_to_hva_cache *ghc = &vcpu->arch.pv_eoi.data; + unsigned long new_len; + if (!IS_ALIGNED(addr, 4)) return 1;

vcpu->arch.pv_eoi.msr_val = data; if (!pv_eoi_enabled(vcpu)) return 0; - return kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.pv_eoi.data, - addr, len); + + if (addr == ghc->gpa && len <= ghc->len) + new_len = ghc->len; + else + new_len = len; + + return kvm_gfn_to_hva_cache_init(vcpu->kvm, ghc, addr, new_len); }

void kvm_apic_accept_events(struct kvm_vcpu *vcpu)