[PATCH] x86/xen: fix percpu vcpu_info allocation

From: Juergen Gross
Date: Fri Nov 24 2023 - 02:55:12 EST


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: 5ead97c84fa7 ("xen: Core Xen implementation")
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
arch/x86/xen/enlighten.c | 6 +++++-
arch/x86/xen/xen-ops.h | 2 +-
2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 0337392a3121..3c61bb98c10e 100644
--- 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
index 408a2aa66c69..a87ab36889e7 100644
--- 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);

--
2.35.3