[OASIS Issue Tracker] (VIRTIO-35) race condition with multi-dword config accesses

[OASIS Issues Tracker <workgroup_mailer@lists.oasis-open.org>]

     [ https://tools.oasis-open.org/issues/browse/VIRTIO-35?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Michael Tsirkin updated VIRTIO-35:
----------------------------------

    Fix Version/s: virtio 1.0 csprd01

> race condition with multi-dword config accesses
> -----------------------------------------------
>
>                 Key: VIRTIO-35
>                 URL: https://tools.oasis-open.org/issues/browse/VIRTIO-35
>             Project: OASIS Virtual I/O Device (VIRTIO) TC
>          Issue Type: Bug
>            Reporter: Michael Tsirkin
>             Fix For: virtio 1.0 csprd01
>
>
> on many architectures, accesses larger than 32 bit can not be atomic.
> Thus access to a device config field of >4 bytes is inherently racy
> in case field can change.
> For example, virtio-blk has
>                 u64 capacity;
> The following race can trigger:
>   driver reads low 32 bit
>   both low and high 32 bit change
>   driver reads high 32 bit
> as a result, capacity observed is composed of
> old low bits and new high bits which does not
> make sense.
> For legacy devices, spec allowed byte by byte access,
> making the race even more common.



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