Re: [Xen-devel] [v4 11/17] vt-d: Add API to update IRTE when VT-d PI is used

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 23/07/15 12:35, Feng Wu wrote:
> +    GET_IREMAP_ENTRY(ir_ctrl->iremap_maddr, remap_index, iremap_entries, p);
> +
> +    old_ire = new_ire = *p;
> +
> +    /* Setup/Update interrupt remapping table entry. */
> +    setup_posted_irte(&new_ire, pi_desc, gvec);
> +    ret = cmpxchg16b(p, &old_ire, &new_ire);
> +
> +    ASSERT(ret == *(__uint128_t *)&old_ire);

This cannot be correct.  Either the cmpxchg() is required and you must
cope with it failing, or the cmpxchg() is not required and this should
be a plain write.

It looks as if the cmpxchg() is required.

~Andrew

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