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xen
23979-xenpaging_document_p2m_mem_paging_functio...
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File 23979-xenpaging_document_p2m_mem_paging_functions.patch of Package xen
changeset: 23979:18306b054799 user: Olaf Hering <olaf@aepfle.de> date: Thu Oct 20 11:25:58 2011 +0100 files: xen/arch/x86/mm/p2m.c description: xenpaging: document p2m_mem_paging functions Add some documentation for each of the p2m_mem_paging functions to describe what they ought to do. Signed-off-by: Olaf Hering <olaf@aepfle.de> Acked-by: Tim Deegan <tim@xen.org> Committed-by: Tim Deegan <tim@xen.org> --- xen/arch/x86/mm/p2m.c | 93 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 93 insertions(+) Index: xen-4.1.2-testing/xen/arch/x86/mm/p2m.c =================================================================== --- xen-4.1.2-testing.orig/xen/arch/x86/mm/p2m.c +++ xen-4.1.2-testing/xen/arch/x86/mm/p2m.c @@ -2838,6 +2838,24 @@ set_shared_p2m_entry(struct p2m_domain * } #ifdef __x86_64__ +/** + * p2m_mem_paging_nominate - Mark a guest page as to-be-paged-out + * @d: guest domain + * @gfn: guest page to nominate + * + * Returns 0 for success or negative errno values if gfn is not pageable. + * + * p2m_mem_paging_nominate() is called by the pager and checks if a guest page + * can be paged out. If the following conditions are met the p2mt will be + * changed: + * - the gfn is backed by a mfn + * - the p2mt of the gfn is pageable + * - the mfn is not used for IO + * - the mfn has exactly one user and has no special meaning + * + * Once the p2mt is changed the page is readonly for the guest. On success the + * pager can write the page contents to disk and later evict the page. + */ int p2m_mem_paging_nominate(struct p2m_domain *p2m, unsigned long gfn) { struct page_info *page; @@ -2883,6 +2901,25 @@ int p2m_mem_paging_nominate(struct p2m_d return ret; } +/** + * p2m_mem_paging_evict - Mark a guest page as paged-out + * @d: guest domain + * @gfn: guest page to evict + * + * Returns 0 for success or negative errno values if eviction is not possible. + * + * p2m_mem_paging_evict() is called by the pager and will free a guest page and + * release it back to Xen. If the following conditions are met the page can be + * freed: + * - the gfn is backed by a mfn + * - the gfn was nominated + * - the mfn has still exactly one user and has no special meaning + * + * After successful nomination some other process could have mapped the page. In + * this case eviction can not be done. If the gfn was populated before the pager + * could evict it, eviction can not be done either. In this case the gfn is + * still backed by a mfn. + */ int p2m_mem_paging_evict(struct p2m_domain *p2m, unsigned long gfn) { struct page_info *page; @@ -2942,6 +2979,15 @@ int p2m_mem_paging_evict(struct p2m_doma return ret; } +/** + * p2m_mem_paging_drop_page - Tell pager to drop its reference to a paged page + * @d: guest domain + * @gfn: guest page to drop + * + * p2m_mem_paging_drop_page() will notify the pager that a paged-out gfn was + * released by the guest. The pager is supposed to drop its reference of the + * gfn. + */ void p2m_mem_paging_drop_page(struct p2m_domain *p2m, unsigned long gfn) { struct vcpu *v = current; @@ -2961,6 +3007,27 @@ void p2m_mem_paging_drop_page(struct p2m } } +/** + * p2m_mem_paging_populate - Tell pager to populete a paged page + * @d: guest domain + * @gfn: guest page in paging state + * + * p2m_mem_paging_populate() will notify the pager that a page in any of the + * paging states needs to be written back into the guest. + * This function needs to be called whenever gfn_to_mfn() returns any of the p2m + * paging types because the gfn may not be backed by a mfn. + * + * The gfn can be in any of the paging states, but the pager needs only be + * notified when the gfn is in the paging-out path (paging_out or paged). This + * function may be called more than once from several vcpus. If the vcpu belongs + * to the guest, the vcpu must be stopped and the pager notified that the vcpu + * was stopped. The pager needs to handle several requests for the same gfn. + * + * If the gfn is not in the paging-out path and the vcpu does not belong to the + * guest, nothing needs to be done and the function assumes that a request was + * already sent to the pager. In this case the caller has to try again until the + * gfn is fully paged in again. + */ void p2m_mem_paging_populate(struct p2m_domain *p2m, unsigned long gfn) { struct vcpu *v = current; @@ -3014,6 +3081,17 @@ void p2m_mem_paging_populate(struct p2m_ mem_event_put_request(d, &d->mem_paging, &req); } +/** + * p2m_mem_paging_prep - Allocate a new page for the guest + * @d: guest domain + * @gfn: guest page in paging state + * + * p2m_mem_paging_prep() will allocate a new page for the guest if the gfn is + * not backed by a mfn. It is called by the pager. + * It is required that the gfn was already populated. The gfn may already have a + * mfn if populate was called for gfn which was nominated but not evicted. In + * this case only the p2mt needs to be forwarded. + */ int p2m_mem_paging_prep(struct p2m_domain *p2m, unsigned long gfn) { struct page_info *page; @@ -3054,6 +3132,21 @@ int p2m_mem_paging_prep(struct p2m_domai return ret; } +/** + * p2m_mem_paging_resume - Resume guest gfn and vcpus + * @d: guest domain + * @gfn: guest page in paging state + * + * p2m_mem_paging_resume() will forward the p2mt of a gfn to ram_rw and all + * waiting vcpus will be unpaused again. It is called by the pager. + * + * The gfn was previously either evicted and populated, or nominated and + * populated. If the page was evicted the p2mt will be p2m_ram_paging_in. If + * the page was just nominated the p2mt will be p2m_ram_paging_in_start because + * the pager did not call p2m_mem_paging_prep(). + * + * If the gfn was dropped the vcpu needs to be unpaused. + */ void p2m_mem_paging_resume(struct p2m_domain *p2m) { struct domain *d = p2m->domain;
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