Merge tag 'for-linus-4.17-rc5-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip

Pull xen fix from Juergen Gross:
 "One fix for the kernel running as a fully virtualized guest using PV
  drivers on old Xen hypervisor versions"

* tag 'for-linus-4.17-rc5-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip:
  x86/xen: Reset VCPU0 info pointer after shared_info remap

1 files changed, 13 insertions, 0 deletions

diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
index 826898701045..19c1ff542387 100644
--- a/arch/x86/xen/enlighten_hvm.c
+++ b/arch/x86/xen/enlighten_hvm.c
@@ -65,6 +65,19 @@ static void __init xen_hvm_init_mem_mapping(void)
 {
         early_memunmap(HYPERVISOR_shared_info, PAGE_SIZE);
         HYPERVISOR_shared_info = __va(PFN_PHYS(shared_info_pfn));
+
+        /*
+         * The virtual address of the shared_info page has changed, so
+         * the vcpu_info pointer for VCPU 0 is now stale.
+         *
+         * The prepare_boot_cpu callback will re-initialize it via
+         * xen_vcpu_setup, but we can't rely on that to be called for
+         * old Xen versions (xen_have_vector_callback == 0).
+         *
+         * It is, in any case, bad to have a stale vcpu_info pointer
+         * so reset it now.
+         */
+        xen_vcpu_info_reset(0);
 }
 
 static void __init init_hvm_pv_info(void)