From: Vitaly Kuznetsov <vkuznets@redhat.com>
Date: Tue, 16 Oct 2018 18:50:05 +0200
Patch-mainline: v4.20-rc1
Subject: x86/kvm/hyperv: don't clear VP assist pages on init
Git-commit: 12e0c6186ba44bb6194cf5d2eda8f46880126587
References: fate#323887
VP assist pages may hold valuable data which needs to be preserved across
migration. Clean PV EOI portion of the data on init, the guest is
responsible for making sure there's no garbage in the rest.
This will be used for nVMX migration, eVMCS address needs to be preserved.
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Olaf Hering <ohering@suse.de>
---
arch/x86/kvm/hyperv.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -1104,7 +1104,13 @@ static int kvm_hv_set_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data, bool host)
addr = kvm_vcpu_gfn_to_hva(vcpu, gfn);
if (kvm_is_error_hva(addr))
return 1;
- if (__clear_user((void __user *)addr, PAGE_SIZE))
+
+ /*
+ * Clear apic_assist portion of f(struct hv_vp_assist_page
+ * only, there can be valuable data in the rest which needs
+ * to be preserved e.g. on migration.
+ */
+ if (__clear_user((void __user *)addr, sizeof(u32)))
return 1;
hv_vcpu->hv_vapic = data;
kvm_vcpu_mark_page_dirty(vcpu, gfn);