* [PATCH] KVM: x86/mmu: Grab nx_lpage_splits as an unsigned long before division
@ 2021-06-15 16:29 Sean Christopherson
2021-06-16 19:01 ` Maxim Levitsky
2021-06-17 17:10 ` Paolo Bonzini
0 siblings, 2 replies; 3+ messages in thread
From: Sean Christopherson @ 2021-06-15 16:29 UTC (permalink / raw)
To: Paolo Bonzini
Cc: Sean Christopherson, Vitaly Kuznetsov, Wanpeng Li, Jim Mattson,
Joerg Roedel, kvm, linux-kernel
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;
--
2.32.0.272.g935e593368-goog
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] KVM: x86/mmu: Grab nx_lpage_splits as an unsigned long before division
2021-06-15 16:29 [PATCH] KVM: x86/mmu: Grab nx_lpage_splits as an unsigned long before division Sean Christopherson
@ 2021-06-16 19:01 ` Maxim Levitsky
2021-06-17 17:10 ` Paolo Bonzini
1 sibling, 0 replies; 3+ messages in thread
From: Maxim Levitsky @ 2021-06-16 19:01 UTC (permalink / raw)
To: Sean Christopherson, Paolo Bonzini
Cc: Vitaly Kuznetsov, Wanpeng Li, Jim Mattson, Joerg Roedel, kvm,
linux-kernel
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
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] KVM: x86/mmu: Grab nx_lpage_splits as an unsigned long before division
2021-06-15 16:29 [PATCH] KVM: x86/mmu: Grab nx_lpage_splits as an unsigned long before division Sean Christopherson
2021-06-16 19:01 ` Maxim Levitsky
@ 2021-06-17 17:10 ` Paolo Bonzini
1 sibling, 0 replies; 3+ messages in thread
From: Paolo Bonzini @ 2021-06-17 17:10 UTC (permalink / raw)
To: Sean Christopherson
Cc: Vitaly Kuznetsov, Wanpeng Li, Jim Mattson, Joerg Roedel, kvm,
linux-kernel
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
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2021-06-17 17:10 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2021-06-15 16:29 [PATCH] KVM: x86/mmu: Grab nx_lpage_splits as an unsigned long before division Sean Christopherson
2021-06-16 19:01 ` Maxim Levitsky
2021-06-17 17:10 ` Paolo Bonzini
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