| Message ID | 20231124074852.25161-1-jgross@suse.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | db2832309a82b9acc4b8cc33a1831d36507ec13e |
| Headers | show |
| Series | x86/xen: fix percpu vcpu_info allocation | expand |
On 11/24/23 2:48 AM, Juergen Gross wrote: > 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@suse.com> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.con> although I am not sure in usefulness of BUILD_BUG_ON --- 64 bytes is part of ABI and hypervisor already has its own BUILD_BUG_ON for this. -boris > @@ -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);
On 27.11.2023 15:57, Boris Ostrovsky wrote: > > > On 11/24/23 2:48 AM, Juergen Gross wrote: >> 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@suse.com> > > Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.con> > > although I am not sure in usefulness of BUILD_BUG_ON --- 64 bytes is part of ABI and hypervisor already has its own BUILD_BUG_ON for this. I understood the check to guard against SMP_CACHE_BYTES < 64. Jan >> @@ -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); >
On 27.11.23 16:00, Jan Beulich wrote: > On 27.11.2023 15:57, Boris Ostrovsky wrote: >> >> >> On 11/24/23 2:48 AM, Juergen Gross wrote: >>> 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@suse.com> >> >> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.con> >> >> although I am not sure in usefulness of BUILD_BUG_ON --- 64 bytes is part of ABI and hypervisor already has its own BUILD_BUG_ON for this. > > I understood the check to guard against SMP_CACHE_BYTES < 64. Yes, that was the idea. Better safe than sorry. Juergen
On Fri, Nov 24, 2023 at 08:48:52AM +0100, Juergen Gross wrote: > 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@suse.com> FWIW, on FreeBSD we also switched to the same approach quite recently: https://cgit.freebsd.org/src/commit/sys/xen/xen_common.c?id=20fc5bf7df1db698f2651eaa04a3bc71290e1636 Should have checked the Linux side, sorry. Roger.
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);
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@suse.com> --- arch/x86/xen/enlighten.c | 6 +++++- arch/x86/xen/xen-ops.h | 2 +- 2 files changed, 6 insertions(+), 2 deletions(-)