Hi, Bibo,
On Wed, Jun 19, 2024 at 4:09 PM Bibo Mao <maobibo@xxxxxxxxxxx> wrote:
>
> When updating pmd entry such as allocating new pmd page or splitting
> huge page into normal page, it is necessary to firstly update all pte
> entries, and then update pmd entry.
>
> It is weak order with LoongArch system, there will be problem if other
> vcpus sees pmd update firstly however pte is not updated. Here smp_wmb()
> is added to assure this.
Memory barriers should be in pairs in most cases. That means you may
lose smp_rmb() in another place.
Huacai
>
> Signed-off-by: Bibo Mao <maobibo@xxxxxxxxxxx>
> ---
> arch/loongarch/kvm/mmu.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/arch/loongarch/kvm/mmu.c b/arch/loongarch/kvm/mmu.c
> index 1690828bd44b..7f04edfbe428 100644
> --- a/arch/loongarch/kvm/mmu.c
> +++ b/arch/loongarch/kvm/mmu.c
> @@ -163,6 +163,7 @@ static kvm_pte_t *kvm_populate_gpa(struct kvm *kvm,
>
> child = kvm_mmu_memory_cache_alloc(cache);
> _kvm_pte_init(child, ctx.invalid_ptes[ctx.level - 1]);
> + smp_wmb(); /* make pte visible before pmd */
> kvm_set_pte(entry, __pa(child));
> } else if (kvm_pte_huge(*entry)) {
> return entry;
> @@ -746,6 +747,7 @@ static kvm_pte_t *kvm_split_huge(struct kvm_vcpu *vcpu, kvm_pte_t *ptep, gfn_t g
> val += PAGE_SIZE;
> }
>
> + smp_wmb();
> /* The later kvm_flush_tlb_gpa() will flush hugepage tlb */
> kvm_set_pte(ptep, __pa(child));
>
> --
> 2.39.3
>
