Re: [PATCH v2 6/8] KVM: Fix multiple races in gfn=>pfn cache refresh

[Lai Jiangshan]

On Wed, Apr 27, 2022 at 7:16 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:

> @@ -159,10 +249,23 @@ int kvm_gfn_to_pfn_cache_refresh(struct kvm *kvm, struct gfn_to_pfn_cache *gpc,
>

The following code of refresh_in_progress is somewhat like mutex.

+ mutex_lock(&gpc->refresh_in_progress); // before write_lock_irq(&gpc->lock);

Is it fit for the intention?

Thanks
Lai

>         write_lock_irq(&gpc->lock);
>
> +       /*
> +        * If another task is refreshing the cache, wait for it to complete.
> +        * There is no guarantee that concurrent refreshes will see the same
> +        * gpa, memslots generation, etc..., so they must be fully serialized.
> +        */
> +       while (gpc->refresh_in_progress) {
> +               write_unlock_irq(&gpc->lock);
> +
> +               cond_resched();
> +
> +               write_lock_irq(&gpc->lock);
> +       }
> +       gpc->refresh_in_progress = true;
> +
>         old_pfn = gpc->pfn;
>         old_khva = gpc->khva - offset_in_page(gpc->khva);
>         old_uhva = gpc->uhva;
> -       old_valid = gpc->valid;
>