+Juergen and Marc On Fri, Nov 05, 2021, Nicholas Piggin wrote: > Increasing the max VCPUs on powerpc makes the kvm_arch member offset > great enough that some assembly breaks due to addressing constants > overflowing field widths. > > Moving the vcpus array to the end of struct kvm prevents this from > happening. It has the side benefit that moving the large array out > from the middle of the structure should help keep other commonly > accessed fields in the same or adjacent cache lines. > > Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx> > --- > > It would next be possible to now make this a dynamically sized array, > and make the KVM_MAX_VCPUS more dynamic Marc has a mostly-baked series to use an xarray[1][2] that AFAICT would be well received. That has my vote, assuming it can get into 5.16. Marc or Juergen, are either of you actively working on that? [1] https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=kvm-arm64/vcpu-xarray [2] https://lkml.kernel.org/r/871r65wwk7.wl-maz@xxxxxxxxxx > however x86 kvm_svm uses its own scheme rather than kvm_arch for some reason. What's the problem in kvm_svm? > Thanks, > Nick > > include/linux/kvm_host.h | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index 0f18df7fe874..78cd9b63a6a5 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -553,7 +553,6 @@ struct kvm { > struct mutex slots_arch_lock; > struct mm_struct *mm; /* userspace tied to this vm */ > struct kvm_memslots __rcu *memslots[KVM_ADDRESS_SPACE_NUM]; > - struct kvm_vcpu *vcpus[KVM_MAX_VCPUS]; > > /* Used to wait for completion of MMU notifiers. */ > spinlock_t mn_invalidate_lock; > @@ -623,6 +622,9 @@ struct kvm { > struct notifier_block pm_notifier; > #endif > char stats_id[KVM_STATS_NAME_SIZE]; > + > + /* This array can be very large, so keep it at the bottom */ > + struct kvm_vcpu *vcpus[KVM_MAX_VCPUS]; > }; > > #define kvm_err(fmt, ...) \ > -- > 2.23.0 >
