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387 lines
10 KiB
387 lines
10 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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* Kernel-based Virtual Machine driver for Linux |
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* |
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* This module enables kernel and guest-mode vCPU access to guest physical |
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* memory with suitable invalidation mechanisms. |
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* |
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* Copyright © 2021 Amazon.com, Inc. or its affiliates. |
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* |
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* Authors: |
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* David Woodhouse <[email protected]> |
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*/ |
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#include <linux/kvm_host.h> |
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#include <linux/kvm.h> |
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#include <linux/highmem.h> |
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#include <linux/module.h> |
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#include <linux/errno.h> |
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#include "kvm_mm.h" |
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/* |
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* MMU notifier 'invalidate_range_start' hook. |
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*/ |
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void gfn_to_pfn_cache_invalidate_start(struct kvm *kvm, unsigned long start, |
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unsigned long end, bool may_block) |
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{ |
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DECLARE_BITMAP(vcpu_bitmap, KVM_MAX_VCPUS); |
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struct gfn_to_pfn_cache *gpc; |
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bool evict_vcpus = false; |
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spin_lock(&kvm->gpc_lock); |
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list_for_each_entry(gpc, &kvm->gpc_list, list) { |
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write_lock_irq(&gpc->lock); |
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/* Only a single page so no need to care about length */ |
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if (gpc->valid && !is_error_noslot_pfn(gpc->pfn) && |
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gpc->uhva >= start && gpc->uhva < end) { |
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gpc->valid = false; |
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/* |
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* If a guest vCPU could be using the physical address, |
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* it needs to be forced out of guest mode. |
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*/ |
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if (gpc->usage & KVM_GUEST_USES_PFN) { |
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if (!evict_vcpus) { |
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evict_vcpus = true; |
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bitmap_zero(vcpu_bitmap, KVM_MAX_VCPUS); |
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} |
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__set_bit(gpc->vcpu->vcpu_idx, vcpu_bitmap); |
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} |
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} |
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write_unlock_irq(&gpc->lock); |
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} |
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spin_unlock(&kvm->gpc_lock); |
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if (evict_vcpus) { |
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/* |
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* KVM needs to ensure the vCPU is fully out of guest context |
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* before allowing the invalidation to continue. |
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*/ |
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unsigned int req = KVM_REQ_OUTSIDE_GUEST_MODE; |
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bool called; |
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/* |
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* If the OOM reaper is active, then all vCPUs should have |
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* been stopped already, so perform the request without |
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* KVM_REQUEST_WAIT and be sad if any needed to be IPI'd. |
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*/ |
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if (!may_block) |
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req &= ~KVM_REQUEST_WAIT; |
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called = kvm_make_vcpus_request_mask(kvm, req, vcpu_bitmap); |
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WARN_ON_ONCE(called && !may_block); |
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} |
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} |
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bool kvm_gfn_to_pfn_cache_check(struct kvm *kvm, struct gfn_to_pfn_cache *gpc, |
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gpa_t gpa, unsigned long len) |
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{ |
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struct kvm_memslots *slots = kvm_memslots(kvm); |
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if ((gpa & ~PAGE_MASK) + len > PAGE_SIZE) |
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return false; |
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if (gpc->gpa != gpa || gpc->generation != slots->generation || |
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kvm_is_error_hva(gpc->uhva)) |
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return false; |
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if (!gpc->valid) |
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return false; |
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return true; |
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} |
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EXPORT_SYMBOL_GPL(kvm_gfn_to_pfn_cache_check); |
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static void gpc_unmap_khva(struct kvm *kvm, kvm_pfn_t pfn, void *khva) |
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{ |
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/* Unmap the old pfn/page if it was mapped before. */ |
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if (!is_error_noslot_pfn(pfn) && khva) { |
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if (pfn_valid(pfn)) |
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kunmap(pfn_to_page(pfn)); |
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#ifdef CONFIG_HAS_IOMEM |
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else |
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memunmap(khva); |
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#endif |
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} |
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} |
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static inline bool mmu_notifier_retry_cache(struct kvm *kvm, unsigned long mmu_seq) |
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{ |
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/* |
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* mn_active_invalidate_count acts for all intents and purposes |
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* like mmu_invalidate_in_progress here; but the latter cannot |
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* be used here because the invalidation of caches in the |
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* mmu_notifier event occurs _before_ mmu_invalidate_in_progress |
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* is elevated. |
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* |
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* Note, it does not matter that mn_active_invalidate_count |
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* is not protected by gpc->lock. It is guaranteed to |
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* be elevated before the mmu_notifier acquires gpc->lock, and |
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* isn't dropped until after mmu_invalidate_seq is updated. |
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*/ |
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if (kvm->mn_active_invalidate_count) |
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return true; |
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/* |
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* Ensure mn_active_invalidate_count is read before |
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* mmu_invalidate_seq. This pairs with the smp_wmb() in |
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* mmu_notifier_invalidate_range_end() to guarantee either the |
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* old (non-zero) value of mn_active_invalidate_count or the |
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* new (incremented) value of mmu_invalidate_seq is observed. |
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*/ |
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smp_rmb(); |
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return kvm->mmu_invalidate_seq != mmu_seq; |
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} |
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static kvm_pfn_t hva_to_pfn_retry(struct kvm *kvm, struct gfn_to_pfn_cache *gpc) |
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{ |
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/* Note, the new page offset may be different than the old! */ |
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void *old_khva = gpc->khva - offset_in_page(gpc->khva); |
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kvm_pfn_t new_pfn = KVM_PFN_ERR_FAULT; |
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void *new_khva = NULL; |
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unsigned long mmu_seq; |
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lockdep_assert_held(&gpc->refresh_lock); |
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lockdep_assert_held_write(&gpc->lock); |
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/* |
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* Invalidate the cache prior to dropping gpc->lock, the gpa=>uhva |
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* assets have already been updated and so a concurrent check() from a |
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* different task may not fail the gpa/uhva/generation checks. |
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*/ |
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gpc->valid = false; |
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do { |
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mmu_seq = kvm->mmu_invalidate_seq; |
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smp_rmb(); |
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write_unlock_irq(&gpc->lock); |
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/* |
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* If the previous iteration "failed" due to an mmu_notifier |
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* event, release the pfn and unmap the kernel virtual address |
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* from the previous attempt. Unmapping might sleep, so this |
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* needs to be done after dropping the lock. Opportunistically |
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* check for resched while the lock isn't held. |
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*/ |
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if (new_pfn != KVM_PFN_ERR_FAULT) { |
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/* |
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* Keep the mapping if the previous iteration reused |
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* the existing mapping and didn't create a new one. |
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*/ |
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if (new_khva != old_khva) |
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gpc_unmap_khva(kvm, new_pfn, new_khva); |
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kvm_release_pfn_clean(new_pfn); |
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cond_resched(); |
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} |
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/* We always request a writeable mapping */ |
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new_pfn = hva_to_pfn(gpc->uhva, false, NULL, true, NULL); |
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if (is_error_noslot_pfn(new_pfn)) |
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goto out_error; |
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/* |
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* Obtain a new kernel mapping if KVM itself will access the |
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* pfn. Note, kmap() and memremap() can both sleep, so this |
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* too must be done outside of gpc->lock! |
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*/ |
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if (gpc->usage & KVM_HOST_USES_PFN) { |
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if (new_pfn == gpc->pfn) { |
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new_khva = old_khva; |
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} else if (pfn_valid(new_pfn)) { |
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new_khva = kmap(pfn_to_page(new_pfn)); |
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#ifdef CONFIG_HAS_IOMEM |
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} else { |
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new_khva = memremap(pfn_to_hpa(new_pfn), PAGE_SIZE, MEMREMAP_WB); |
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#endif |
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} |
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if (!new_khva) { |
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kvm_release_pfn_clean(new_pfn); |
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goto out_error; |
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} |
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} |
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write_lock_irq(&gpc->lock); |
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/* |
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* Other tasks must wait for _this_ refresh to complete before |
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* attempting to refresh. |
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*/ |
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WARN_ON_ONCE(gpc->valid); |
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} while (mmu_notifier_retry_cache(kvm, mmu_seq)); |
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gpc->valid = true; |
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gpc->pfn = new_pfn; |
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gpc->khva = new_khva + (gpc->gpa & ~PAGE_MASK); |
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/* |
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* Put the reference to the _new_ pfn. The pfn is now tracked by the |
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* cache and can be safely migrated, swapped, etc... as the cache will |
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* invalidate any mappings in response to relevant mmu_notifier events. |
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*/ |
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kvm_release_pfn_clean(new_pfn); |
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return 0; |
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out_error: |
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write_lock_irq(&gpc->lock); |
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return -EFAULT; |
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} |
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int kvm_gfn_to_pfn_cache_refresh(struct kvm *kvm, struct gfn_to_pfn_cache *gpc, |
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gpa_t gpa, unsigned long len) |
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{ |
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struct kvm_memslots *slots = kvm_memslots(kvm); |
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unsigned long page_offset = gpa & ~PAGE_MASK; |
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kvm_pfn_t old_pfn, new_pfn; |
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unsigned long old_uhva; |
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void *old_khva; |
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int ret = 0; |
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/* |
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* If must fit within a single page. The 'len' argument is |
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* only to enforce that. |
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*/ |
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if (page_offset + len > PAGE_SIZE) |
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return -EINVAL; |
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/* |
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* If another task is refreshing the cache, wait for it to complete. |
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* There is no guarantee that concurrent refreshes will see the same |
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* gpa, memslots generation, etc..., so they must be fully serialized. |
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*/ |
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mutex_lock(&gpc->refresh_lock); |
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write_lock_irq(&gpc->lock); |
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old_pfn = gpc->pfn; |
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old_khva = gpc->khva - offset_in_page(gpc->khva); |
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old_uhva = gpc->uhva; |
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/* If the userspace HVA is invalid, refresh that first */ |
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if (gpc->gpa != gpa || gpc->generation != slots->generation || |
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kvm_is_error_hva(gpc->uhva)) { |
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gfn_t gfn = gpa_to_gfn(gpa); |
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gpc->gpa = gpa; |
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gpc->generation = slots->generation; |
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gpc->memslot = __gfn_to_memslot(slots, gfn); |
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gpc->uhva = gfn_to_hva_memslot(gpc->memslot, gfn); |
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if (kvm_is_error_hva(gpc->uhva)) { |
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ret = -EFAULT; |
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goto out; |
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} |
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} |
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/* |
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* If the userspace HVA changed or the PFN was already invalid, |
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* drop the lock and do the HVA to PFN lookup again. |
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*/ |
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if (!gpc->valid || old_uhva != gpc->uhva) { |
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ret = hva_to_pfn_retry(kvm, gpc); |
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} else { |
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/* If the HVA→PFN mapping was already valid, don't unmap it. */ |
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old_pfn = KVM_PFN_ERR_FAULT; |
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old_khva = NULL; |
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} |
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out: |
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/* |
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* Invalidate the cache and purge the pfn/khva if the refresh failed. |
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* Some/all of the uhva, gpa, and memslot generation info may still be |
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* valid, leave it as is. |
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*/ |
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if (ret) { |
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gpc->valid = false; |
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gpc->pfn = KVM_PFN_ERR_FAULT; |
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gpc->khva = NULL; |
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} |
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/* Snapshot the new pfn before dropping the lock! */ |
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new_pfn = gpc->pfn; |
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write_unlock_irq(&gpc->lock); |
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mutex_unlock(&gpc->refresh_lock); |
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if (old_pfn != new_pfn) |
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gpc_unmap_khva(kvm, old_pfn, old_khva); |
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return ret; |
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} |
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EXPORT_SYMBOL_GPL(kvm_gfn_to_pfn_cache_refresh); |
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void kvm_gfn_to_pfn_cache_unmap(struct kvm *kvm, struct gfn_to_pfn_cache *gpc) |
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{ |
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void *old_khva; |
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kvm_pfn_t old_pfn; |
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mutex_lock(&gpc->refresh_lock); |
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write_lock_irq(&gpc->lock); |
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gpc->valid = false; |
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old_khva = gpc->khva - offset_in_page(gpc->khva); |
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old_pfn = gpc->pfn; |
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/* |
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* We can leave the GPA → uHVA map cache intact but the PFN |
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* lookup will need to be redone even for the same page. |
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*/ |
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gpc->khva = NULL; |
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gpc->pfn = KVM_PFN_ERR_FAULT; |
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write_unlock_irq(&gpc->lock); |
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mutex_unlock(&gpc->refresh_lock); |
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gpc_unmap_khva(kvm, old_pfn, old_khva); |
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} |
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EXPORT_SYMBOL_GPL(kvm_gfn_to_pfn_cache_unmap); |
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int kvm_gfn_to_pfn_cache_init(struct kvm *kvm, struct gfn_to_pfn_cache *gpc, |
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struct kvm_vcpu *vcpu, enum pfn_cache_usage usage, |
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gpa_t gpa, unsigned long len) |
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{ |
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WARN_ON_ONCE(!usage || (usage & KVM_GUEST_AND_HOST_USE_PFN) != usage); |
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if (!gpc->active) { |
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rwlock_init(&gpc->lock); |
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mutex_init(&gpc->refresh_lock); |
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gpc->khva = NULL; |
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gpc->pfn = KVM_PFN_ERR_FAULT; |
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gpc->uhva = KVM_HVA_ERR_BAD; |
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gpc->vcpu = vcpu; |
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gpc->usage = usage; |
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gpc->valid = false; |
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gpc->active = true; |
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spin_lock(&kvm->gpc_lock); |
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list_add(&gpc->list, &kvm->gpc_list); |
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spin_unlock(&kvm->gpc_lock); |
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} |
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return kvm_gfn_to_pfn_cache_refresh(kvm, gpc, gpa, len); |
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} |
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EXPORT_SYMBOL_GPL(kvm_gfn_to_pfn_cache_init); |
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void kvm_gfn_to_pfn_cache_destroy(struct kvm *kvm, struct gfn_to_pfn_cache *gpc) |
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{ |
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if (gpc->active) { |
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spin_lock(&kvm->gpc_lock); |
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list_del(&gpc->list); |
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spin_unlock(&kvm->gpc_lock); |
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kvm_gfn_to_pfn_cache_unmap(kvm, gpc); |
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gpc->active = false; |
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} |
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} |
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EXPORT_SYMBOL_GPL(kvm_gfn_to_pfn_cache_destroy);
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