On 25/07/2025 4:06 pm, Edwin Török wrote: > Linux already has a similar BUILD_BUG_ON. > Currently this struct is ~224 bytes on x86-64. > > No functional change. > > Signed-off-by: Edwin Török <edwin.to...@cloud.com> > --- > xen/arch/x86/cpu/vpmu.c | 1 + > xen/include/public/pmu.h | 3 +++ > 2 files changed, 4 insertions(+) > > diff --git a/xen/arch/x86/cpu/vpmu.c b/xen/arch/x86/cpu/vpmu.c > index c28192ea26..7be79c2d00 100644 > --- a/xen/arch/x86/cpu/vpmu.c > +++ b/xen/arch/x86/cpu/vpmu.c > @@ -401,6 +401,7 @@ static int vpmu_arch_initialise(struct vcpu *v) > uint8_t vendor = current_cpu_data.x86_vendor; > int ret; > > + BUILD_BUG_ON(sizeof(struct xen_pmu_data) > PAGE_SIZE); > BUILD_BUG_ON(sizeof(struct xen_pmu_intel_ctxt) > XENPMU_CTXT_PAD_SZ); > BUILD_BUG_ON(sizeof(struct xen_pmu_amd_ctxt) > XENPMU_CTXT_PAD_SZ); > BUILD_BUG_ON(sizeof(struct xen_pmu_regs) > XENPMU_REGS_PAD_SZ);
This is fine (even if it ought to be elsewhere, but don't worry about that). > diff --git a/xen/include/public/pmu.h b/xen/include/public/pmu.h > index af8b7babdd..15decc024d 100644 > --- a/xen/include/public/pmu.h > +++ b/xen/include/public/pmu.h > @@ -93,6 +93,9 @@ DEFINE_XEN_GUEST_HANDLE(xen_pmu_params_t); > * Architecture-independent fields of xen_pmu_data are WO for the hypervisor > * and RO for the guest but some fields in xen_pmu_arch can be writable > * by both the hypervisor and the guest (see arch-$arch/pmu.h). > + * > + * PAGE_SIZE bytes of memory are allocated. > + * This struct cannot be larger than PAGE_SIZE. This isn't. Xen's PAGE_SIZE is not necessarily the same as PAGE_SIZE in the guest consuming this header. This highlights one of the problems that Xen's ABI entrenches. Being x86-only, it's 4k in practice, but there's no easy solution. I'd just skip this comment. Anything else is going to get tied up in unrelated bigger problems. ~Andrew
