Re: [PATCH 2/8] KVM: pfncache: add a mark-dirty helper

[David Woodhouse]

On Thu, 2023-09-14 at 08:49 +0000, Paul Durrant wrote:
> --- a/arch/x86/kvm/xen.c
> +++ b/arch/x86/kvm/xen.c
> @@ -430,14 +430,13 @@ static void kvm_xen_update_runstate_guest(struct kvm_vcpu *v, bool atomic)
>                 smp_wmb();
>         }
>  
> -       if (user_len2)
> +       if (user_len2) {
> +               kvm_gpc_mark_dirty(gpc2);
>                 read_unlock(&gpc2->lock);
> +       }
>  
> +       kvm_gpc_mark_dirty(gpc1);
>         read_unlock_irqrestore(&gpc1->lock, flags);
> -
> -       mark_page_dirty_in_slot(v->kvm, gpc1->memslot, gpc1->gpa >> PAGE_SHIFT);
> -       if (user_len2)
> -               mark_page_dirty_in_slot(v->kvm, gpc2->memslot, gpc2->gpa >> PAGE_SHIFT);
>  }
>  
>  void kvm_xen_update_runstate(struct kvm_vcpu *v, int state)

ISTR there was a reason why the mark_page_dirty_in_slot() was called
*after* unlocking. Although now I say it, that seems wrong... is that
because the spinlock is only protecting the uHVA→kHVA mapping, while
the memslot/gpa are going to remain valid even after unlock, because
those are protected by sRCU?

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