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

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Date:   Thu, 28 Apr 2022 11:39:35 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Mingwei Zhang <mizhang@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: Re: [PATCH v2 6/8] KVM: Fix multiple races in gfn=>pfn cache refresh

On Wed, Apr 27, 2022 at 7:16 PM Sean Christopherson <seanjc@...gle.com> 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;
>