// 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 evict_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 forced out of guest mode.
*/
if (gpc->usage & KVM_GUEST_USES_PFN) {
if (!evict_vcpus) {
evict_vcpus = true;
bitmap_zero(vcpu_bitmap, KVM_MAX_VCPUS);
}
__set_bit(gpc->vcpu->vcpu_idx, vcpu_bitmap);
}
}
write_unlock_irq(&gpc->lock);
}
spin_unlock(&kvm->gpc_lock);
if (evict_vcpus) {
/*
* KVM needs to ensure the vCPU is fully out of guest context
* before allowing the invalidation to continue.
*/
unsigned int req = KVM_REQ_OUTSIDE_GUEST_MODE;
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 IPI'd.
*/
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)
{
/* 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, false);
}
}
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)
{
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;
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;
/* 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->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)) {
gpc->pfn = KVM_PFN_ERR_FAULT;
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->usage & KVM_HOST_USES_PFN) {
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:
write_unlock_irq(&gpc->lock);
__release_gpc(kvm, old_pfn, old_khva, old_gpa);
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;
gpa_t old_gpa;
write_lock_irq(&gpc->lock);
gpc->valid = false;
old_khva = gpc->khva - offset_in_page(gpc->khva);
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);
}
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, enum pfn_cache_usage usage,
gpa_t gpa, unsigned long len)
{
WARN_ON_ONCE(!usage || (usage & KVM_GUEST_AND_HOST_USE_PFN) != usage);
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->usage = usage;
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);
}
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);