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|
// SPDX-License-Identifier: GPL-2.0
/*
* Secure pages management: Migration of pages between normal and secure
* memory of KVM guests.
*
* Copyright 2018 Bharata B Rao, IBM Corp. <bharata@linux.ibm.com>
*/
/*
* A pseries guest can be run as secure guest on Ultravisor-enabled
* POWER platforms. On such platforms, this driver will be used to manage
* the movement of guest pages between the normal memory managed by
* hypervisor (HV) and secure memory managed by Ultravisor (UV).
*
* The page-in or page-out requests from UV will come to HV as hcalls and
* HV will call back into UV via ultracalls to satisfy these page requests.
*
* Private ZONE_DEVICE memory equal to the amount of secure memory
* available in the platform for running secure guests is hotplugged.
* Whenever a page belonging to the guest becomes secure, a page from this
* private device memory is used to represent and track that secure page
* on the HV side. Some pages (like virtio buffers, VPA pages etc) are
* shared between UV and HV. However such pages aren't represented by
* device private memory and mappings to shared memory exist in both
* UV and HV page tables.
*/
/*
* Notes on locking
*
* kvm->arch.uvmem_lock is a per-guest lock that prevents concurrent
* page-in and page-out requests for the same GPA. Concurrent accesses
* can either come via UV (guest vCPUs requesting for same page)
* or when HV and guest simultaneously access the same page.
* This mutex serializes the migration of page from HV(normal) to
* UV(secure) and vice versa. So the serialization points are around
* migrate_vma routines and page-in/out routines.
*
* Per-guest mutex comes with a cost though. Mainly it serializes the
* fault path as page-out can occur when HV faults on accessing secure
* guest pages. Currently UV issues page-in requests for all the guest
* PFNs one at a time during early boot (UV_ESM uvcall), so this is
* not a cause for concern. Also currently the number of page-outs caused
* by HV touching secure pages is very very low. If an when UV supports
* overcommitting, then we might see concurrent guest driven page-outs.
*
* Locking order
*
* 1. kvm->srcu - Protects KVM memslots
* 2. kvm->mm->mmap_lock - find_vma, migrate_vma_pages and helpers, ksm_madvise
* 3. kvm->arch.uvmem_lock - protects read/writes to uvmem slots thus acting
* as sync-points for page-in/out
*/
/*
* Notes on page size
*
* Currently UV uses 2MB mappings internally, but will issue H_SVM_PAGE_IN
* and H_SVM_PAGE_OUT hcalls in PAGE_SIZE(64K) granularity. HV tracks
* secure GPAs at 64K page size and maintains one device PFN for each
* 64K secure GPA. UV_PAGE_IN and UV_PAGE_OUT calls by HV are also issued
* for 64K page at a time.
*
* HV faulting on secure pages: When HV touches any secure page, it
* faults and issues a UV_PAGE_OUT request with 64K page size. Currently
* UV splits and remaps the 2MB page if necessary and copies out the
* required 64K page contents.
*
* Shared pages: Whenever guest shares a secure page, UV will split and
* remap the 2MB page if required and issue H_SVM_PAGE_IN with 64K page size.
*
* HV invalidating a page: When a regular page belonging to secure
* guest gets unmapped, HV informs UV with UV_PAGE_INVAL of 64K
* page size. Using 64K page size is correct here because any non-secure
* page will essentially be of 64K page size. Splitting by UV during sharing
* and page-out ensures this.
*
* Page fault handling: When HV handles page fault of a page belonging
* to secure guest, it sends that to UV with a 64K UV_PAGE_IN request.
* Using 64K size is correct here too as UV would have split the 2MB page
* into 64k mappings and would have done page-outs earlier.
*
* In summary, the current secure pages handling code in HV assumes
* 64K page size and in fact fails any page-in/page-out requests of
* non-64K size upfront. If and when UV starts supporting multiple
* page-sizes, we need to break this assumption.
*/
#include <linux/pagemap.h>
#include <linux/migrate.h>
#include <linux/kvm_host.h>
#include <linux/ksm.h>
#include <asm/ultravisor.h>
#include <asm/mman.h>
#include <asm/kvm_ppc.h>
#include <asm/kvm_book3s_uvmem.h>
static struct dev_pagemap kvmppc_uvmem_pgmap;
static unsigned long *kvmppc_uvmem_bitmap;
static DEFINE_SPINLOCK(kvmppc_uvmem_bitmap_lock);
/*
* States of a GFN
* ---------------
* The GFN can be in one of the following states.
*
* (a) Secure - The GFN is secure. The GFN is associated with
* a Secure VM, the contents of the GFN is not accessible
* to the Hypervisor. This GFN can be backed by a secure-PFN,
* or can be backed by a normal-PFN with contents encrypted.
* The former is true when the GFN is paged-in into the
* ultravisor. The latter is true when the GFN is paged-out
* of the ultravisor.
*
* (b) Shared - The GFN is shared. The GFN is associated with a
* a secure VM. The contents of the GFN is accessible to
* Hypervisor. This GFN is backed by a normal-PFN and its
* content is un-encrypted.
*
* (c) Normal - The GFN is a normal. The GFN is associated with
* a normal VM. The contents of the GFN is accesible to
* the Hypervisor. Its content is never encrypted.
*
* States of a VM.
* ---------------
*
* Normal VM: A VM whose contents are always accessible to
* the hypervisor. All its GFNs are normal-GFNs.
*
* Secure VM: A VM whose contents are not accessible to the
* hypervisor without the VM's consent. Its GFNs are
* either Shared-GFN or Secure-GFNs.
*
* Transient VM: A Normal VM that is transitioning to secure VM.
* The transition starts on successful return of
* H_SVM_INIT_START, and ends on successful return
* of H_SVM_INIT_DONE. This transient VM, can have GFNs
* in any of the three states; i.e Secure-GFN, Shared-GFN,
* and Normal-GFN. The VM never executes in this state
* in supervisor-mode.
*
* Memory slot State.
* -----------------------------
* The state of a memory slot mirrors the state of the
* VM the memory slot is associated with.
*
* VM State transition.
* --------------------
*
* A VM always starts in Normal Mode.
*
* H_SVM_INIT_START moves the VM into transient state. During this
* time the Ultravisor may request some of its GFNs to be shared or
* secured. So its GFNs can be in one of the three GFN states.
*
* H_SVM_INIT_DONE moves the VM entirely from transient state to
* secure-state. At this point any left-over normal-GFNs are
* transitioned to Secure-GFN.
*
* H_SVM_INIT_ABORT moves the transient VM back to normal VM.
* All its GFNs are moved to Normal-GFNs.
*
* UV_TERMINATE transitions the secure-VM back to normal-VM. All
* the secure-GFN and shared-GFNs are tranistioned to normal-GFN
* Note: The contents of the normal-GFN is undefined at this point.
*
* GFN state implementation:
* -------------------------
*
* Secure GFN is associated with a secure-PFN; also called uvmem_pfn,
* when the GFN is paged-in. Its pfn[] has KVMPPC_GFN_UVMEM_PFN flag
* set, and contains the value of the secure-PFN.
* It is associated with a normal-PFN; also called mem_pfn, when
* the GFN is pagedout. Its pfn[] has KVMPPC_GFN_MEM_PFN flag set.
* The value of the normal-PFN is not tracked.
*
* Shared GFN is associated with a normal-PFN. Its pfn[] has
* KVMPPC_UVMEM_SHARED_PFN flag set. The value of the normal-PFN
* is not tracked.
*
* Normal GFN is associated with normal-PFN. Its pfn[] has
* no flag set. The value of the normal-PFN is not tracked.
*
* Life cycle of a GFN
* --------------------
*
* --------------------------------------------------------------
* | | Share | Unshare | SVM |H_SVM_INIT_DONE|
* | |operation |operation | abort/ | |
* | | | | terminate | |
* -------------------------------------------------------------
* | | | | | |
* | Secure | Shared | Secure |Normal |Secure |
* | | | | | |
* | Shared | Shared | Secure |Normal |Shared |
* | | | | | |
* | Normal | Shared | Secure |Normal |Secure |
* --------------------------------------------------------------
*
* Life cycle of a VM
* --------------------
*
* --------------------------------------------------------------------
* | | start | H_SVM_ |H_SVM_ |H_SVM_ |UV_SVM_ |
* | | VM |INIT_START|INIT_DONE|INIT_ABORT |TERMINATE |
* | | | | | | |
* --------- ----------------------------------------------------------
* | | | | | | |
* | Normal | Normal | Transient|Error |Error |Normal |
* | | | | | | |
* | Secure | Error | Error |Error |Error |Normal |
* | | | |
|