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For the shared info page and for grant tables, Xen shares its own pages from the "Xen heap" to the guest. The guest requests that a given page from a certain address space (XENMAPSPACE_shared_info, etc.) be mapped to a given GPA using the XENMEM_add_to_physmap hypercall. To support that in qemu when *emulating* Xen, create a memory region (migratable) and allow it to be mapped as an overlay when requested. Xen theoretically allows the same page to be mapped multiple times into the guest, but that's hard to track and reinstate over migration, so we automatically *unmap* any previous mapping when creating a new one. This approach has been used in production with.... a non-trivial number of guests expecting true Xen, without any problems yet being noticed. This adds just the shared info page for now. The grant tables will be a larger region, and will need to be overlaid one page at a time. I think that means I need to create separate aliases for each page of the overall grant_frames region, so that they can be mapped individually. Signed-off-by: David Woodhouse <dwmw@amazon.co.uk> Reviewed-by: Paul Durrant <paul@xen.org>
20 lines
533 B
C
20 lines
533 B
C
/*
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* QEMU Xen emulation: Shared/overlay pages support
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*
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* Copyright © 2022 Amazon.com, Inc. or its affiliates. All Rights Reserved.
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*
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* Authors: David Woodhouse <dwmw2@infradead.org>
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*
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* This work is licensed under the terms of the GNU GPL, version 2 or later.
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* See the COPYING file in the top-level directory.
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*/
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#ifndef QEMU_XEN_OVERLAY_H
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#define QEMU_XEN_OVERLAY_H
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void xen_overlay_create(void);
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int xen_overlay_map_shinfo_page(uint64_t gpa);
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void *xen_overlay_get_shinfo_ptr(void);
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#endif /* QEMU_XEN_OVERLAY_H */
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