Re: [Qemu-devel] [PATCH] memory.h: Improve IOMMU related documentation

[Peter Maydell]

On 30 April 2018 at 13:24, Peter Maydell <address@hidden> wrote:
> Add more detail to the documentation for memory_region_init_iommu()
> and other IOMMU-related functions and data structures.

> @@ -203,20 +211,58 @@ typedef struct IOMMUMemoryRegionClass {
>       * be the access permission of this translation operation. We can
>       * set flag to IOMMU_NONE to mean that we don't need any
>       * read/write permission checks, like, when for region replay.
> +     *
> +     * Once the IOMMU has returned a TLB entry, it must notify
> +     * the IOMMU's users if that TLB entry changes, using
> +     * memory_region_notify_iommu() (or, if necessary, by calling
> +     * memory_region_notify_one() for each registered notifier).
> +     *
> +     * @iommu: the IOMMUMemoryRegion
> +     * @hwaddr: address to be translated within the memory region
> +     * @flag: requested access permissions
>       */
>      IOMMUTLBEntry (*translate)(IOMMUMemoryRegion *iommu, hwaddr addr,
>                                 IOMMUAccessFlags flag);

A question I just thought of -- how long is the IOMMUTLBEntry I get
back guaranteed to be valid for? For instance if I'm in an RCU
critical section can I assume it won't become invalid before I
leave the critical section? Or must I always register an IOMMU
notifier before I call translate? I'm guessing not the latter
because flatview_do_translate() does not, but is the guarantee
only RCU-critical section or while-holding-big-QEMU-lock or
something else?

thanks
-- PMM