Re: [Xen-devel] [PATCH] x86/hvm: don't rely on shared ioreq state for completion handling

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 31/07/15 16:34, Paul Durrant wrote:
> Both hvm_io_pending() and hvm_wait_for_io() use the shared (with emulator)
> ioreq structure to determined whether there is a pending I/O. The latter will
> misbehave if the shared state is driven to STATE_IOREQ_NONE by the emulator,
> or when the shared ioreq page is cleared for re-insertion into the guest
> P2M when the ioreq server is disabled (STATE_IOREQ_NONE == 0) because it
> will terminate its wait without calling hvm_io_assist() to adjust Xen's
> internal I/O emulation state. This may then lead to an io completion
> handler finding incorrect internal emulation state and calling
> domain_crash().
>
> This patch fixes the problem by adding a pending flag to the ioreq server's
> per-vcpu structure which cannot be directly manipulated by the emulator
> and thus can be used to determine whether an I/O is actually pending for
> that vcpu on that ioreq server. If an I/O is pending and the shared state
> is seen to go to STATE_IOREQ_NONE then it can be treated as an abnormal
> completion of emulation (hence the data placed in the shared structure
> is not used) and the internal state is adjusted as for a normal completion.
> Thus, when a completion handler subsequently runs, the internal state is as
> expected and domain_crash() will not be called.
>
> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> Reported-by: Sander Eikelenboom <linux@xxxxxxxxxxxxxx>
> Tested-by: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
> Cc: Keir Fraser <keir@xxxxxxx>
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

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