diff options
Diffstat (limited to 'virt/kvm/pfncache.c')
| -rw-r--r-- | virt/kvm/pfncache.c | 337 |
1 files changed, 337 insertions, 0 deletions
diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c new file mode 100644 index 000000000000..ce878f4be4da --- /dev/null +++ b/virt/kvm/pfncache.c @@ -0,0 +1,337 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Kernel-based Virtual Machine driver for Linux + * + * This module enables kernel and guest-mode vCPU access to guest physical + * memory with suitable invalidation mechanisms. + * + * Copyright © 2021 Amazon.com, Inc. or its affiliates. + * + * Authors: + * David Woodhouse <dwmw2@infradead.org> + */ + +#include <linux/kvm_host.h> +#include <linux/kvm.h> +#include <linux/highmem.h> +#include <linux/module.h> +#include <linux/errno.h> + +#include "kvm_mm.h" + +/* + * MMU notifier 'invalidate_range_start' hook. + */ +void gfn_to_pfn_cache_invalidate_start(struct kvm *kvm, unsigned long start, + unsigned long end, bool may_block) +{ + DECLARE_BITMAP(vcpu_bitmap, KVM_MAX_VCPUS); + struct gfn_to_pfn_cache *gpc; + bool wake_vcpus = false; + + spin_lock(&kvm->gpc_lock); + list_for_each_entry(gpc, &kvm->gpc_list, list) { + write_lock_irq(&gpc->lock); + + /* Only a single page so no need to care about length */ + if (gpc->valid && !is_error_noslot_pfn(gpc->pfn) && + gpc->uhva >= start && gpc->uhva < end) { + gpc->valid = false; + + /* + * If a guest vCPU could be using the physical address, + * it needs to be woken. + */ + if (gpc->guest_uses_pa) { + if (!wake_vcpus) { + wake_vcpus = true; + bitmap_zero(vcpu_bitmap, KVM_MAX_VCPUS); + } + __set_bit(gpc->vcpu->vcpu_idx, vcpu_bitmap); + } + + /* + * We cannot call mark_page_dirty() from here because + * this physical CPU might not have an active vCPU + * with which to do the KVM dirty tracking. + * + * Neither is there any point in telling the kernel MM + * that the underlying page is dirty. A vCPU in guest + * mode might still be writing to it up to the point + * where we wake them a few lines further down anyway. + * + * So all the dirty marking happens on the unmap. + */ + } + write_unlock_irq(&gpc->lock); + } + spin_unlock(&kvm->gpc_lock); + + if (wake_vcpus) { + unsigned int req = KVM_REQ_GPC_INVALIDATE; + bool called; + + /* + * If the OOM reaper is active, then all vCPUs should have + * been stopped already, so perform the request without + * KVM_REQUEST_WAIT and be sad if any needed to be woken. + */ + if (!may_block) + req &= ~KVM_REQUEST_WAIT; + + called = kvm_make_vcpus_request_mask(kvm, req, vcpu_bitmap); + + WARN_ON_ONCE(called && !may_block); + } +} + +bool kvm_gfn_to_pfn_cache_check(struct kvm *kvm, struct gfn_to_pfn_cache *gpc, + gpa_t gpa, unsigned long len) +{ + struct kvm_memslots *slots = kvm_memslots(kvm); + + if ((gpa & ~PAGE_MASK) + len > PAGE_SIZE) + return false; + + if (gpc->gpa != gpa || gpc->generation != slots->generation || + kvm_is_error_hva(gpc->uhva)) + return false; + + if (!gpc->valid) + return false; + + return true; +} +EXPORT_SYMBOL_GPL(kvm_gfn_to_pfn_cache_check); + +static void __release_gpc(struct kvm *kvm, kvm_pfn_t pfn, void *khva, + gpa_t gpa, bool dirty) +{ + /* Unmap the old page if it was mapped before, and release it */ + if (!is_error_noslot_pfn(pfn)) { + if (khva) { + if (pfn_valid(pfn)) + kunmap(pfn_to_page(pfn)); +#ifdef CONFIG_HAS_IOMEM + else + memunmap(khva); +#endif + } + + kvm_release_pfn(pfn, dirty); + if (dirty) + mark_page_dirty(kvm, gpa); + } +} + +static kvm_pfn_t hva_to_pfn_retry(struct kvm *kvm, unsigned long uhva) +{ + unsigned long mmu_seq; + kvm_pfn_t new_pfn; + int retry; + + do { + mmu_seq = kvm->mmu_notifier_seq; + smp_rmb(); + + /* We always request a writeable mapping */ + new_pfn = hva_to_pfn(uhva, false, NULL, true, NULL); + if (is_error_noslot_pfn(new_pfn)) + break; + + KVM_MMU_READ_LOCK(kvm); + retry = mmu_notifier_retry_hva(kvm, mmu_seq, uhva); + KVM_MMU_READ_UNLOCK(kvm); + if (!retry) + break; + + cond_resched(); + } while (1); + + return new_pfn; +} + +int kvm_gfn_to_pfn_cache_refresh(struct kvm *kvm, struct gfn_to_pfn_cache *gpc, + gpa_t gpa, unsigned long len, bool dirty) +{ + struct kvm_memslots *slots = kvm_memslots(kvm); + unsigned long page_offset = gpa & ~PAGE_MASK; + kvm_pfn_t old_pfn, new_pfn; + unsigned long old_uhva; + gpa_t old_gpa; + void *old_khva; + bool old_valid, old_dirty; + int ret = 0; + + /* + * If must fit within a single page. The 'len' argument is + * only to enforce that. + */ + if (page_offset + len > PAGE_SIZE) + return -EINVAL; + + write_lock_irq(&gpc->lock); + + old_gpa = gpc->gpa; + old_pfn = gpc->pfn; + old_khva = gpc->khva - offset_in_page(gpc->khva); + old_uhva = gpc->uhva; + old_valid = gpc->valid; + old_dirty = gpc->dirty; + + /* If the userspace HVA is invalid, refresh that first */ + if (gpc->gpa != gpa || gpc->generation != slots->generation || + kvm_is_error_hva(gpc->uhva)) { + gfn_t gfn = gpa_to_gfn(gpa); + + gpc->dirty = false; + gpc->gpa = gpa; + gpc->generation = slots->generation; + gpc->memslot = __gfn_to_memslot(slots, gfn); + gpc->uhva = gfn_to_hva_memslot(gpc->memslot, gfn); + + if (kvm_is_error_hva(gpc->uhva)) { + ret = -EFAULT; + goto out; + } + + gpc->uhva += page_offset; + } + + /* + * If the userspace HVA changed or the PFN was already invalid, + * drop the lock and do the HVA to PFN lookup again. + */ + if (!old_valid || old_uhva != gpc->uhva) { + unsigned long uhva = gpc->uhva; + void *new_khva = NULL; + + /* Placeholders for "hva is valid but not yet mapped" */ + gpc->pfn = KVM_PFN_ERR_FAULT; + gpc->khva = NULL; + gpc->valid = true; + + write_unlock_irq(&gpc->lock); + + new_pfn = hva_to_pfn_retry(kvm, uhva); + if (is_error_noslot_pfn(new_pfn)) { + ret = -EFAULT; + goto map_done; + } + + if (gpc->kernel_map) { + if (new_pfn == old_pfn) { + new_khva = old_khva; + old_pfn = KVM_PFN_ERR_FAULT; + old_khva = NULL; + } else if (pfn_valid(new_pfn)) { + new_khva = kmap(pfn_to_page(new_pfn)); +#ifdef CONFIG_HAS_IOMEM + } else { + new_khva = memremap(pfn_to_hpa(new_pfn), PAGE_SIZE, MEMREMAP_WB); +#endif + } + if (new_khva) + new_khva += page_offset; + else + ret = -EFAULT; + } + + map_done: + write_lock_irq(&gpc->lock); + if (ret) { + gpc->valid = false; + gpc->pfn = KVM_PFN_ERR_FAULT; + gpc->khva = NULL; + } else { + /* At this point, gpc->valid may already have been cleared */ + gpc->pfn = new_pfn; + gpc->khva = new_khva; + } + } else { + /* If the HVA→PFN mapping was already valid, don't unmap it. */ + old_pfn = KVM_PFN_ERR_FAULT; + old_khva = NULL; + } + + out: + if (ret) + gpc->dirty = false; + else + gpc->dirty = dirty; + + write_unlock_irq(&gpc->lock); + + __release_gpc(kvm, old_pfn, old_khva, old_gpa, old_dirty); + + return ret; +} +EXPORT_SYMBOL_GPL(kvm_gfn_to_pfn_cache_refresh); + +void kvm_gfn_to_pfn_cache_unmap(struct kvm *kvm, struct gfn_to_pfn_cache *gpc) +{ + void *old_khva; + kvm_pfn_t old_pfn; + bool old_dirty; + gpa_t old_gpa; + + write_lock_irq(&gpc->lock); + + gpc->valid = false; + + old_khva = gpc->khva - offset_in_page(gpc->khva); + old_dirty = gpc->dirty; + old_gpa = gpc->gpa; + old_pfn = gpc->pfn; + + /* + * We can leave the GPA → uHVA map cache intact but the PFN + * lookup will need to be redone even for the same page. + */ + gpc->khva = NULL; + gpc->pfn = KVM_PFN_ERR_FAULT; + + write_unlock_irq(&gpc->lock); + + __release_gpc(kvm, old_pfn, old_khva, old_gpa, old_dirty); +} +EXPORT_SYMBOL_GPL(kvm_gfn_to_pfn_cache_unmap); + + +int kvm_gfn_to_pfn_cache_init(struct kvm *kvm, struct gfn_to_pfn_cache *gpc, + struct kvm_vcpu *vcpu, bool guest_uses_pa, + bool kernel_map, gpa_t gpa, unsigned long len, + bool dirty) +{ + if (!gpc->active) { + rwlock_init(&gpc->lock); + + gpc->khva = NULL; + gpc->pfn = KVM_PFN_ERR_FAULT; + gpc->uhva = KVM_HVA_ERR_BAD; + gpc->vcpu = vcpu; + gpc->kernel_map = kernel_map; + gpc->guest_uses_pa = guest_uses_pa; + gpc->valid = false; + gpc->active = true; + + spin_lock(&kvm->gpc_lock); + list_add(&gpc->list, &kvm->gpc_list); + spin_unlock(&kvm->gpc_lock); + } + return kvm_gfn_to_pfn_cache_refresh(kvm, gpc, gpa, len, dirty); +} +EXPORT_SYMBOL_GPL(kvm_gfn_to_pfn_cache_init); + +void kvm_gfn_to_pfn_cache_destroy(struct kvm *kvm, struct gfn_to_pfn_cache *gpc) +{ + if (gpc->active) { + spin_lock(&kvm->gpc_lock); + list_del(&gpc->list); + spin_unlock(&kvm->gpc_lock); + + kvm_gfn_to_pfn_cache_unmap(kvm, gpc); + gpc->active = false; + } +} +EXPORT_SYMBOL_GPL(kvm_gfn_to_pfn_cache_destroy); |