linux-kernel - Re: [PATCH net V4] vhost: log dirty page correctly

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Message-Id: <20190117.115855.725358558291814993.davem@davemloft.net>
Date:   Thu, 17 Jan 2019 11:58:55 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     jasowang@...hat.com
Cc:     mst@...hat.com, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, jintack@...columbia.edu
Subject: Re: [PATCH net V4] vhost: log dirty page correctly

From: Jason Wang <jasowang@...hat.com>
Date: Wed, 16 Jan 2019 16:54:42 +0800

> Vhost dirty page logging API is designed to sync through GPA. But we
> try to log GIOVA when device IOTLB is enabled. This is wrong and may
> lead to missing data after migration.
> 
> To solve this issue, when logging with device IOTLB enabled, we will:
> 
> 1) reuse the device IOTLB translation result of GIOVA->HVA mapping to
>    get HVA, for writable descriptor, get HVA through iovec. For used
>    ring update, translate its GIOVA to HVA
> 2) traverse the GPA->HVA mapping to get the possible GPA and log
>    through GPA. Pay attention this reverse mapping is not guaranteed
>    to be unique, so we should log each possible GPA in this case.
> 
> This fix the failure of scp to guest during migration. In -next, we
> will probably support passing GIOVA->GPA instead of GIOVA->HVA.
> 
> Fixes: 6b1e6cc7855b ("vhost: new device IOTLB API")
> Reported-by: Jintack Lim <jintack@...columbia.edu>
> Cc: Jintack Lim <jintack@...columbia.edu>
> Signed-off-by: Jason Wang <jasowang@...hat.com>

Michaell, can I get a review for this please?

Thank you.