| Message ID | 20210615162905.2132937-1-seanjc@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: x86/mmu: Grab nx_lpage_splits as an unsigned long before division | expand |
On Tue, 2021-06-15 at 09:29 -0700, Sean Christopherson wrote: > Snapshot kvm->stats.nx_lpage_splits into a local unsigned long to avoid > 64-bit division on 32-bit kernels. Casting to an unsigned long is safe > because the maximum number of shadow pages, n_max_mmu_pages, is also an > unsigned long, i.e. KVM will start recycling shadow pages before the > number of splits can exceed a 32-bit value. > > ERROR: modpost: "__udivdi3" [arch/x86/kvm/kvm.ko] undefined! > > Fixes: 7ee093d4f3f5 ("KVM: switch per-VM stats to u64") > Signed-off-by: Sean Christopherson <seanjc@google.com> > --- > arch/x86/kvm/mmu/mmu.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 720ceb0a1f5c..7d3e57678d34 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -6043,6 +6043,7 @@ static int set_nx_huge_pages_recovery_ratio(const char *val, const struct kernel > > static void kvm_recover_nx_lpages(struct kvm *kvm) > { > + unsigned long nx_lpage_splits = kvm->stat.nx_lpage_splits; > int rcu_idx; > struct kvm_mmu_page *sp; > unsigned int ratio; > @@ -6054,7 +6055,7 @@ static void kvm_recover_nx_lpages(struct kvm *kvm) > write_lock(&kvm->mmu_lock); > > ratio = READ_ONCE(nx_huge_pages_recovery_ratio); > - to_zap = ratio ? DIV_ROUND_UP(kvm->stat.nx_lpage_splits, ratio) : 0; > + to_zap = ratio ? DIV_ROUND_UP(nx_lpage_splits, ratio) : 0; > for ( ; to_zap; --to_zap) { > if (list_empty(&kvm->arch.lpage_disallowed_mmu_pages)) > break; Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com> Best regards, Maxim Levitsky
On 15/06/21 18:29, Sean Christopherson wrote: > Snapshot kvm->stats.nx_lpage_splits into a local unsigned long to avoid > 64-bit division on 32-bit kernels. Casting to an unsigned long is safe > because the maximum number of shadow pages, n_max_mmu_pages, is also an > unsigned long, i.e. KVM will start recycling shadow pages before the > number of splits can exceed a 32-bit value. > > ERROR: modpost: "__udivdi3" [arch/x86/kvm/kvm.ko] undefined! > > Fixes: 7ee093d4f3f5 ("KVM: switch per-VM stats to u64") > Signed-off-by: Sean Christopherson <seanjc@google.com> > --- > arch/x86/kvm/mmu/mmu.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 720ceb0a1f5c..7d3e57678d34 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -6043,6 +6043,7 @@ static int set_nx_huge_pages_recovery_ratio(const char *val, const struct kernel > > static void kvm_recover_nx_lpages(struct kvm *kvm) > { > + unsigned long nx_lpage_splits = kvm->stat.nx_lpage_splits; > int rcu_idx; > struct kvm_mmu_page *sp; > unsigned int ratio; > @@ -6054,7 +6055,7 @@ static void kvm_recover_nx_lpages(struct kvm *kvm) > write_lock(&kvm->mmu_lock); > > ratio = READ_ONCE(nx_huge_pages_recovery_ratio); > - to_zap = ratio ? DIV_ROUND_UP(kvm->stat.nx_lpage_splits, ratio) : 0; > + to_zap = ratio ? DIV_ROUND_UP(nx_lpage_splits, ratio) : 0; > for ( ; to_zap; --to_zap) { > if (list_empty(&kvm->arch.lpage_disallowed_mmu_pages)) > break; > Queued, thanks. Paolo
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 720ceb0a1f5c..7d3e57678d34 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -6043,6 +6043,7 @@ static int set_nx_huge_pages_recovery_ratio(const char *val, const struct kernel static void kvm_recover_nx_lpages(struct kvm *kvm) { + unsigned long nx_lpage_splits = kvm->stat.nx_lpage_splits; int rcu_idx; struct kvm_mmu_page *sp; unsigned int ratio; @@ -6054,7 +6055,7 @@ static void kvm_recover_nx_lpages(struct kvm *kvm) write_lock(&kvm->mmu_lock); ratio = READ_ONCE(nx_huge_pages_recovery_ratio); - to_zap = ratio ? DIV_ROUND_UP(kvm->stat.nx_lpage_splits, ratio) : 0; + to_zap = ratio ? DIV_ROUND_UP(nx_lpage_splits, ratio) : 0; for ( ; to_zap; --to_zap) { if (list_empty(&kvm->arch.lpage_disallowed_mmu_pages)) break;
Snapshot kvm->stats.nx_lpage_splits into a local unsigned long to avoid 64-bit division on 32-bit kernels. Casting to an unsigned long is safe because the maximum number of shadow pages, n_max_mmu_pages, is also an unsigned long, i.e. KVM will start recycling shadow pages before the number of splits can exceed a 32-bit value. ERROR: modpost: "__udivdi3" [arch/x86/kvm/kvm.ko] undefined! Fixes: 7ee093d4f3f5 ("KVM: switch per-VM stats to u64") Signed-off-by: Sean Christopherson <seanjc@google.com> --- arch/x86/kvm/mmu/mmu.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)