x86/xen: fix percpu vcpu_info allocation

Today the percpu struct vcpu_info is allocated via DEFINE_PER_CPU(), meaning that it could cross a page boundary. In this case registering it with the hypervisor will fail, resulting in a panic(). This can easily be fixed by using DEFINE_PER_CPU_ALIGNED() instead, as struct vcpu_info is guaranteed to have a size of 64 bytes, matching the cache line size of x86 64-bit processors (Xen doesn't support 32-bit processors). Fixes: 5ead97c ("xen: Core Xen implementation") Signed-off-by: Juergen Gross <[email protected]> Reviewed-by: Boris Ostrovsky <[email protected]> Link: https://lore.kernel.org/r/[email protected] Signed-off-by: Juergen Gross <[email protected]>
raspberrypi · Nov 28, 2023 · db28323 · db28323
1 parent 7bf9a6b
commit db28323
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Showing 2 changed files with 6 additions and 2 deletions.
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
@@ -33,9 +33,12 @@ EXPORT_SYMBOL_GPL(hypercall_page);
  * and xen_vcpu_setup for details. By default it points to share_info->vcpu_info
  * but during boot it is switched to point to xen_vcpu_info.
  * The pointer is used in xen_evtchn_do_upcall to acknowledge pending events.
+ * Make sure that xen_vcpu_info doesn't cross a page boundary by making it
+ * cache-line aligned (the struct is guaranteed to have a size of 64 bytes,
+ * which matches the cache line size of 64-bit x86 processors).
  */
 DEFINE_PER_CPU(struct vcpu_info *, xen_vcpu);
-DEFINE_PER_CPU(struct vcpu_info, xen_vcpu_info);
+DEFINE_PER_CPU_ALIGNED(struct vcpu_info, xen_vcpu_info);
 
 /* Linux <-> Xen vCPU id mapping */
 DEFINE_PER_CPU(uint32_t, xen_vcpu_id);
@@ -160,6 +163,7 @@ void xen_vcpu_setup(int cpu)
 	int err;
 	struct vcpu_info *vcpup;
 
+	BUILD_BUG_ON(sizeof(*vcpup) > SMP_CACHE_BYTES);
 	BUG_ON(HYPERVISOR_shared_info == &xen_dummy_shared_info);
 
 	/*

diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
@@ -21,7 +21,7 @@ extern void *xen_initial_gdt;
 struct trap_info;
 void xen_copy_trap_info(struct trap_info *traps);
 
-DECLARE_PER_CPU(struct vcpu_info, xen_vcpu_info);
+DECLARE_PER_CPU_ALIGNED(struct vcpu_info, xen_vcpu_info);
 DECLARE_PER_CPU(unsigned long, xen_cr3);
 DECLARE_PER_CPU(unsigned long, xen_current_cr3);