virt/kvm/pfncache.c - linux - Git at Google

 // 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)
 {
 	struct gfn_to_pfn_cache *gpc;

 	spin_lock(&kvm->gpc_lock);
 	list_for_each_entry(gpc, &kvm->gpc_list, list) {
 		read_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) {
 			read_unlock_irq(&gpc->lock);

 			/*
 			 * There is a small window here where the cache could
 			 * be modified, and invalidation would no longer be
 			 * necessary. Hence check again whether invalidation
 			 * is still necessary once the write lock has been
 			 * acquired.
 			 */

 			write_lock_irq(&gpc->lock);
 			if (gpc->valid && !is_error_noslot_pfn(gpc->pfn) &&
 			    gpc->uhva >= start && gpc->uhva < end)
 				gpc->valid = false;
 			write_unlock_irq(&gpc->lock);
 			continue;
 		}

 		read_unlock_irq(&gpc->lock);
 	}
 	spin_unlock(&kvm->gpc_lock);
 }

 bool kvm_gpc_check(struct gfn_to_pfn_cache *gpc, unsigned long len)
 {
 	struct kvm_memslots *slots = kvm_memslots(gpc->kvm);

 	if (!gpc->active)
 		return false;

 	/*
 	 * If the page was cached from a memslot, make sure the memslots have
 	 * not been re-configured.
 	 */
 	if (!kvm_is_error_gpa(gpc->gpa) && gpc->generation != slots->generation)
 		return false;

 	if (kvm_is_error_hva(gpc->uhva))
 		return false;

 	if (offset_in_page(gpc->uhva) + len > PAGE_SIZE)
 		return false;

 	if (!gpc->valid)
 		return false;

 	return true;
 }

 static void *gpc_map(kvm_pfn_t pfn)
 {
 	if (pfn_valid(pfn))
 		return kmap(pfn_to_page(pfn));

 #ifdef CONFIG_HAS_IOMEM
 	return memremap(pfn_to_hpa(pfn), PAGE_SIZE, MEMREMAP_WB);
 #else
 	return NULL;
 #endif
 }

 static void gpc_unmap(kvm_pfn_t pfn, void *khva)
 {
 	/* Unmap the old pfn/page if it was mapped before. */
 	if (is_error_noslot_pfn(pfn) || !khva)
 		return;

 	if (pfn_valid(pfn)) {
 		kunmap(pfn_to_page(pfn));
 		return;
 	}

 #ifdef CONFIG_HAS_IOMEM
 	memunmap(khva);
 #endif
 }

 static inline bool mmu_notifier_retry_cache(struct kvm *kvm, unsigned long mmu_seq)
 {
 	/*
 	 * mn_active_invalidate_count acts for all intents and purposes
 	 * like mmu_invalidate_in_progress here; but the latter cannot
 	 * be used here because the invalidation of caches in the
 	 * mmu_notifier event occurs _before_ mmu_invalidate_in_progress
 	 * is elevated.
 	 *
 	 * Note, it does not matter that mn_active_invalidate_count
 	 * is not protected by gpc->lock.  It is guaranteed to
 	 * be elevated before the mmu_notifier acquires gpc->lock, and
 	 * isn't dropped until after mmu_invalidate_seq is updated.
 	 */
 	if (kvm->mn_active_invalidate_count)
 		return true;

 	/*
 	 * Ensure mn_active_invalidate_count is read before
 	 * mmu_invalidate_seq.  This pairs with the smp_wmb() in
 	 * mmu_notifier_invalidate_range_end() to guarantee either the
 	 * old (non-zero) value of mn_active_invalidate_count or the
 	 * new (incremented) value of mmu_invalidate_seq is observed.
 	 */
 	smp_rmb();
 	return kvm->mmu_invalidate_seq != mmu_seq;
 }

 static kvm_pfn_t hva_to_pfn_retry(struct gfn_to_pfn_cache *gpc)
 {
 	/* Note, the new page offset may be different than the old! */
 	void *old_khva = (void *)PAGE_ALIGN_DOWN((uintptr_t)gpc->khva);
 	kvm_pfn_t new_pfn = KVM_PFN_ERR_FAULT;
 	void *new_khva = NULL;
 	unsigned long mmu_seq;

 	lockdep_assert_held(&gpc->refresh_lock);

 	lockdep_assert_held_write(&gpc->lock);

 	/*
 	 * Invalidate the cache prior to dropping gpc->lock, the gpa=>uhva
 	 * assets have already been updated and so a concurrent check() from a
 	 * different task may not fail the gpa/uhva/generation checks.
 	 */
 	gpc->valid = false;

 	do {
 		mmu_seq = gpc->kvm->mmu_invalidate_seq;
 		smp_rmb();

 		write_unlock_irq(&gpc->lock);

 		/*
 		 * If the previous iteration "failed" due to an mmu_notifier
 		 * event, release the pfn and unmap the kernel virtual address
 		 * from the previous attempt.  Unmapping might sleep, so this
 		 * needs to be done after dropping the lock.  Opportunistically
 		 * check for resched while the lock isn't held.
 		 */
 		if (new_pfn != KVM_PFN_ERR_FAULT) {
 			/*
 			 * Keep the mapping if the previous iteration reused
 			 * the existing mapping and didn't create a new one.
 			 */
 			if (new_khva != old_khva)
 				gpc_unmap(new_pfn, new_khva);

 			kvm_release_pfn_clean(new_pfn);

 			cond_resched();
 		}

 		/* We always request a writeable mapping */
 		new_pfn = hva_to_pfn(gpc->uhva, false, false, NULL, true, NULL);
 		if (is_error_noslot_pfn(new_pfn))
 			goto out_error;

 		/*
 		 * Obtain a new kernel mapping if KVM itself will access the
 		 * pfn.  Note, kmap() and memremap() can both sleep, so this
 		 * too must be done outside of gpc->lock!
 		 */
 		if (new_pfn == gpc->pfn)
 			new_khva = old_khva;
 		else
 			new_khva = gpc_map(new_pfn);

 		if (!new_khva) {
 			kvm_release_pfn_clean(new_pfn);
 			goto out_error;
 		}

 		write_lock_irq(&gpc->lock);

 		/*
 		 * Other tasks must wait for _this_ refresh to complete before
 		 * attempting to refresh.
 		 */
 		WARN_ON_ONCE(gpc->valid);
 	} while (mmu_notifier_retry_cache(gpc->kvm, mmu_seq));

 	gpc->valid = true;
 	gpc->pfn = new_pfn;
 	gpc->khva = new_khva + offset_in_page(gpc->uhva);

 	/*
 	 * Put the reference to the _new_ pfn.  The pfn is now tracked by the
 	 * cache and can be safely migrated, swapped, etc... as the cache will
 	 * invalidate any mappings in response to relevant mmu_notifier events.
 	 */
 	kvm_release_pfn_clean(new_pfn);

 	return 0;

 out_error:
 	write_lock_irq(&gpc->lock);

 	return -EFAULT;
 }

 static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long uhva,
 			     unsigned long len)
 {
 	unsigned long page_offset;
 	bool unmap_old = false;
 	unsigned long old_uhva;
 	kvm_pfn_t old_pfn;
 	bool hva_change = false;
 	void *old_khva;
 	int ret;

 	/* Either gpa or uhva must be valid, but not both */
 	if (WARN_ON_ONCE(kvm_is_error_gpa(gpa) == kvm_is_error_hva(uhva)))
 		return -EINVAL;

 	/*
 	 * The cached acces must fit within a single page. The 'len' argument
 	 * exists only to enforce that.
 	 */
 	page_offset = kvm_is_error_gpa(gpa) ? offset_in_page(uhva) :
 					      offset_in_page(gpa);
 	if (page_offset + len > PAGE_SIZE)
 		return -EINVAL;

 	lockdep_assert_held(&gpc->refresh_lock);

 	write_lock_irq(&gpc->lock);

 	if (!gpc->active) {
 		ret = -EINVAL;
 		goto out_unlock;
 	}

 	old_pfn = gpc->pfn;
 	old_khva = (void *)PAGE_ALIGN_DOWN((uintptr_t)gpc->khva);
 	old_uhva = PAGE_ALIGN_DOWN(gpc->uhva);

 	if (kvm_is_error_gpa(gpa)) {
 		gpc->gpa = INVALID_GPA;
 		gpc->memslot = NULL;
 		gpc->uhva = PAGE_ALIGN_DOWN(uhva);

 		if (gpc->uhva != old_uhva)
 			hva_change = true;
 	} else {
 		struct kvm_memslots *slots = kvm_memslots(gpc->kvm);

 		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)) {
 				ret = -EFAULT;
 				goto out;
 			}

 			/*
 			 * Even if the GPA and/or the memslot generation changed, the
 			 * HVA may still be the same.
 			 */
 			if (gpc->uhva != old_uhva)
 				hva_change = true;
 		} else {
 			gpc->uhva = old_uhva;
 		}
 	}

 	/* Note: the offset must be correct before calling hva_to_pfn_retry() */
 	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 (!gpc->valid || hva_change) {
 		ret = hva_to_pfn_retry(gpc);
 	} else {
 		/*
 		 * If the HVA→PFN mapping was already valid, don't unmap it.
 		 * But do update gpc->khva because the offset within the page
 		 * may have changed.
 		 */
 		gpc->khva = old_khva + page_offset;
 		ret = 0;
 		goto out_unlock;
 	}

  out:
 	/*
 	 * Invalidate the cache and purge the pfn/khva if the refresh failed.
 	 * Some/all of the uhva, gpa, and memslot generation info may still be
 	 * valid, leave it as is.
 	 */
 	if (ret) {
 		gpc->valid = false;
 		gpc->pfn = KVM_PFN_ERR_FAULT;
 		gpc->khva = NULL;
 	}

 	/* Detect a pfn change before dropping the lock! */
 	unmap_old = (old_pfn != gpc->pfn);

 out_unlock:
 	write_unlock_irq(&gpc->lock);

 	if (unmap_old)
 		gpc_unmap(old_pfn, old_khva);

 	return ret;
 }

 int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, unsigned long len)
 {
 	unsigned long uhva;

 	guard(mutex)(&gpc->refresh_lock);

 	/*
 	 * If the GPA is valid then ignore the HVA, as a cache can be GPA-based
 	 * or HVA-based, not both.  For GPA-based caches, the HVA will be
 	 * recomputed during refresh if necessary.
 	 */
 	uhva = kvm_is_error_gpa(gpc->gpa) ? gpc->uhva : KVM_HVA_ERR_BAD;

 	return __kvm_gpc_refresh(gpc, gpc->gpa, uhva, len);
 }

 void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm)
 {
 	rwlock_init(&gpc->lock);
 	mutex_init(&gpc->refresh_lock);

 	gpc->kvm = kvm;
 	gpc->pfn = KVM_PFN_ERR_FAULT;
 	gpc->gpa = INVALID_GPA;
 	gpc->uhva = KVM_HVA_ERR_BAD;
 	gpc->active = gpc->valid = false;
 }

 static int __kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long uhva,
 			      unsigned long len)
 {
 	struct kvm *kvm = gpc->kvm;

 	guard(mutex)(&gpc->refresh_lock);

 	if (!gpc->active) {
 		if (KVM_BUG_ON(gpc->valid, kvm))
 			return -EIO;

 		spin_lock(&kvm->gpc_lock);
 		list_add(&gpc->list, &kvm->gpc_list);
 		spin_unlock(&kvm->gpc_lock);

 		/*
 		 * Activate the cache after adding it to the list, a concurrent
 		 * refresh must not establish a mapping until the cache is
 		 * reachable by mmu_notifier events.
 		 */
 		write_lock_irq(&gpc->lock);
 		gpc->active = true;
 		write_unlock_irq(&gpc->lock);
 	}
 	return __kvm_gpc_refresh(gpc, gpa, uhva, len);
 }

 int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
 {
 	return __kvm_gpc_activate(gpc, gpa, KVM_HVA_ERR_BAD, len);
 }

 int kvm_gpc_activate_hva(struct gfn_to_pfn_cache *gpc, unsigned long uhva, unsigned long len)
 {
 	return __kvm_gpc_activate(gpc, INVALID_GPA, uhva, len);
 }

 void kvm_gpc_deactivate(struct gfn_to_pfn_cache *gpc)
 {
 	struct kvm *kvm = gpc->kvm;
 	kvm_pfn_t old_pfn;
 	void *old_khva;

 	guard(mutex)(&gpc->refresh_lock);

 	if (gpc->active) {
 		/*
 		 * Deactivate the cache before removing it from the list, KVM
 		 * must stall mmu_notifier events until all users go away, i.e.
 		 * until gpc->lock is dropped and refresh is guaranteed to fail.
 		 */
 		write_lock_irq(&gpc->lock);
 		gpc->active = false;
 		gpc->valid = false;

 		/*
 		 * Leave the GPA => uHVA cache intact, it's protected by the
 		 * memslot generation.  The PFN lookup needs to be redone every
 		 * time as mmu_notifier protection is lost when the cache is
 		 * removed from the VM's gpc_list.
 		 */
 		old_khva = gpc->khva - offset_in_page(gpc->khva);
 		gpc->khva = NULL;

 		old_pfn = gpc->pfn;
 		gpc->pfn = KVM_PFN_ERR_FAULT;
 		write_unlock_irq(&gpc->lock);

 		spin_lock(&kvm->gpc_lock);
 		list_del(&gpc->list);
 		spin_unlock(&kvm->gpc_lock);

 		gpc_unmap(old_pfn, old_khva);
 	}
 }
	// 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)
	{
	struct gfn_to_pfn_cache *gpc;

	spin_lock(&kvm->gpc_lock);
	list_for_each_entry(gpc, &kvm->gpc_list, list) {
	read_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) {
	read_unlock_irq(&gpc->lock);

	/*
	* There is a small window here where the cache could
	* be modified, and invalidation would no longer be
	* necessary. Hence check again whether invalidation
	* is still necessary once the write lock has been
	* acquired.
	*/

	write_lock_irq(&gpc->lock);
	if (gpc->valid && !is_error_noslot_pfn(gpc->pfn) &&
	gpc->uhva >= start && gpc->uhva < end)
	gpc->valid = false;
	write_unlock_irq(&gpc->lock);
	continue;
	}

	read_unlock_irq(&gpc->lock);
	}
	spin_unlock(&kvm->gpc_lock);
	}

	bool kvm_gpc_check(struct gfn_to_pfn_cache *gpc, unsigned long len)
	{
	struct kvm_memslots *slots = kvm_memslots(gpc->kvm);

	if (!gpc->active)
	return false;

	/*
	* If the page was cached from a memslot, make sure the memslots have
	* not been re-configured.
	*/
	if (!kvm_is_error_gpa(gpc->gpa) && gpc->generation != slots->generation)
	return false;

	if (kvm_is_error_hva(gpc->uhva))
	return false;

	if (offset_in_page(gpc->uhva) + len > PAGE_SIZE)
	return false;

	if (!gpc->valid)
	return false;

	return true;
	}

	static void *gpc_map(kvm_pfn_t pfn)
	{
	if (pfn_valid(pfn))
	return kmap(pfn_to_page(pfn));

	#ifdef CONFIG_HAS_IOMEM
	return memremap(pfn_to_hpa(pfn), PAGE_SIZE, MEMREMAP_WB);
	#else
	return NULL;
	#endif
	}

	static void gpc_unmap(kvm_pfn_t pfn, void *khva)
	{
	/* Unmap the old pfn/page if it was mapped before. */
	if (is_error_noslot_pfn(pfn) \|\| !khva)
	return;

	if (pfn_valid(pfn)) {
	kunmap(pfn_to_page(pfn));
	return;
	}

	#ifdef CONFIG_HAS_IOMEM
	memunmap(khva);
	#endif
	}

	static inline bool mmu_notifier_retry_cache(struct kvm *kvm, unsigned long mmu_seq)
	{
	/*
	* mn_active_invalidate_count acts for all intents and purposes
	* like mmu_invalidate_in_progress here; but the latter cannot
	* be used here because the invalidation of caches in the
	* mmu_notifier event occurs _before_ mmu_invalidate_in_progress
	* is elevated.
	*
	* Note, it does not matter that mn_active_invalidate_count
	* is not protected by gpc->lock. It is guaranteed to
	* be elevated before the mmu_notifier acquires gpc->lock, and
	* isn't dropped until after mmu_invalidate_seq is updated.
	*/
	if (kvm->mn_active_invalidate_count)
	return true;

	/*
	* Ensure mn_active_invalidate_count is read before
	* mmu_invalidate_seq. This pairs with the smp_wmb() in
	* mmu_notifier_invalidate_range_end() to guarantee either the
	* old (non-zero) value of mn_active_invalidate_count or the
	* new (incremented) value of mmu_invalidate_seq is observed.
	*/
	smp_rmb();
	return kvm->mmu_invalidate_seq != mmu_seq;
	}

	static kvm_pfn_t hva_to_pfn_retry(struct gfn_to_pfn_cache *gpc)
	{
	/* Note, the new page offset may be different than the old! */
	void old_khva = (void )PAGE_ALIGN_DOWN((uintptr_t)gpc->khva);
	kvm_pfn_t new_pfn = KVM_PFN_ERR_FAULT;
	void *new_khva = NULL;
	unsigned long mmu_seq;

	lockdep_assert_held(&gpc->refresh_lock);

	lockdep_assert_held_write(&gpc->lock);

	/*
	* Invalidate the cache prior to dropping gpc->lock, the gpa=>uhva
	* assets have already been updated and so a concurrent check() from a
	* different task may not fail the gpa/uhva/generation checks.
	*/
	gpc->valid = false;

	do {
	mmu_seq = gpc->kvm->mmu_invalidate_seq;
	smp_rmb();

	write_unlock_irq(&gpc->lock);

	/*
	* If the previous iteration "failed" due to an mmu_notifier
	* event, release the pfn and unmap the kernel virtual address
	* from the previous attempt. Unmapping might sleep, so this
	* needs to be done after dropping the lock. Opportunistically
	* check for resched while the lock isn't held.
	*/
	if (new_pfn != KVM_PFN_ERR_FAULT) {
	/*
	* Keep the mapping if the previous iteration reused
	* the existing mapping and didn't create a new one.
	*/
	if (new_khva != old_khva)
	gpc_unmap(new_pfn, new_khva);

	kvm_release_pfn_clean(new_pfn);

	cond_resched();
	}

	/* We always request a writeable mapping */
	new_pfn = hva_to_pfn(gpc->uhva, false, false, NULL, true, NULL);
	if (is_error_noslot_pfn(new_pfn))
	goto out_error;

	/*
	* Obtain a new kernel mapping if KVM itself will access the
	* pfn. Note, kmap() and memremap() can both sleep, so this
	* too must be done outside of gpc->lock!
	*/
	if (new_pfn == gpc->pfn)
	new_khva = old_khva;
	else
	new_khva = gpc_map(new_pfn);

	if (!new_khva) {
	kvm_release_pfn_clean(new_pfn);
	goto out_error;
	}

	write_lock_irq(&gpc->lock);

	/*
	* Other tasks must wait for _this_ refresh to complete before
	* attempting to refresh.
	*/
	WARN_ON_ONCE(gpc->valid);
	} while (mmu_notifier_retry_cache(gpc->kvm, mmu_seq));

	gpc->valid = true;
	gpc->pfn = new_pfn;
	gpc->khva = new_khva + offset_in_page(gpc->uhva);

	/*
	* Put the reference to the _new_ pfn. The pfn is now tracked by the
	* cache and can be safely migrated, swapped, etc... as the cache will
	* invalidate any mappings in response to relevant mmu_notifier events.
	*/
	kvm_release_pfn_clean(new_pfn);

	return 0;

	out_error:
	write_lock_irq(&gpc->lock);

	return -EFAULT;
	}

	static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long uhva,
	unsigned long len)
	{
	unsigned long page_offset;
	bool unmap_old = false;
	unsigned long old_uhva;
	kvm_pfn_t old_pfn;
	bool hva_change = false;
	void *old_khva;
	int ret;

	/* Either gpa or uhva must be valid, but not both */
	if (WARN_ON_ONCE(kvm_is_error_gpa(gpa) == kvm_is_error_hva(uhva)))
	return -EINVAL;

	/*
	* The cached acces must fit within a single page. The 'len' argument
	* exists only to enforce that.
	*/
	page_offset = kvm_is_error_gpa(gpa) ? offset_in_page(uhva) :
	offset_in_page(gpa);
	if (page_offset + len > PAGE_SIZE)
	return -EINVAL;

	lockdep_assert_held(&gpc->refresh_lock);

	write_lock_irq(&gpc->lock);

	if (!gpc->active) {
	ret = -EINVAL;
	goto out_unlock;
	}

	old_pfn = gpc->pfn;
	old_khva = (void *)PAGE_ALIGN_DOWN((uintptr_t)gpc->khva);
	old_uhva = PAGE_ALIGN_DOWN(gpc->uhva);

	if (kvm_is_error_gpa(gpa)) {
	gpc->gpa = INVALID_GPA;
	gpc->memslot = NULL;
	gpc->uhva = PAGE_ALIGN_DOWN(uhva);

	if (gpc->uhva != old_uhva)
	hva_change = true;
	} else {
	struct kvm_memslots *slots = kvm_memslots(gpc->kvm);

	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)) {
	ret = -EFAULT;
	goto out;
	}

	/*
	* Even if the GPA and/or the memslot generation changed, the
	* HVA may still be the same.
	*/
	if (gpc->uhva != old_uhva)
	hva_change = true;
	} else {
	gpc->uhva = old_uhva;
	}
	}

	/* Note: the offset must be correct before calling hva_to_pfn_retry() */
	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 (!gpc->valid \|\| hva_change) {
	ret = hva_to_pfn_retry(gpc);
	} else {
	/*
	* If the HVA→PFN mapping was already valid, don't unmap it.
	* But do update gpc->khva because the offset within the page
	* may have changed.
	*/
	gpc->khva = old_khva + page_offset;
	ret = 0;
	goto out_unlock;
	}

	out:
	/*
	* Invalidate the cache and purge the pfn/khva if the refresh failed.
	* Some/all of the uhva, gpa, and memslot generation info may still be
	* valid, leave it as is.
	*/
	if (ret) {
	gpc->valid = false;
	gpc->pfn = KVM_PFN_ERR_FAULT;
	gpc->khva = NULL;
	}

	/* Detect a pfn change before dropping the lock! */
	unmap_old = (old_pfn != gpc->pfn);

	out_unlock:
	write_unlock_irq(&gpc->lock);

	if (unmap_old)
	gpc_unmap(old_pfn, old_khva);

	return ret;
	}

	int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, unsigned long len)
	{
	unsigned long uhva;

	guard(mutex)(&gpc->refresh_lock);

	/*
	* If the GPA is valid then ignore the HVA, as a cache can be GPA-based
	* or HVA-based, not both. For GPA-based caches, the HVA will be
	* recomputed during refresh if necessary.
	*/
	uhva = kvm_is_error_gpa(gpc->gpa) ? gpc->uhva : KVM_HVA_ERR_BAD;

	return __kvm_gpc_refresh(gpc, gpc->gpa, uhva, len);
	}

	void kvm_gpc_init(struct gfn_to_pfn_cache gpc, struct kvm kvm)
	{
	rwlock_init(&gpc->lock);
	mutex_init(&gpc->refresh_lock);

	gpc->kvm = kvm;
	gpc->pfn = KVM_PFN_ERR_FAULT;
	gpc->gpa = INVALID_GPA;
	gpc->uhva = KVM_HVA_ERR_BAD;
	gpc->active = gpc->valid = false;
	}

	static int __kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long uhva,
	unsigned long len)
	{
	struct kvm *kvm = gpc->kvm;

	guard(mutex)(&gpc->refresh_lock);

	if (!gpc->active) {
	if (KVM_BUG_ON(gpc->valid, kvm))
	return -EIO;

	spin_lock(&kvm->gpc_lock);
	list_add(&gpc->list, &kvm->gpc_list);
	spin_unlock(&kvm->gpc_lock);

	/*
	* Activate the cache after adding it to the list, a concurrent
	* refresh must not establish a mapping until the cache is
	* reachable by mmu_notifier events.
	*/
	write_lock_irq(&gpc->lock);
	gpc->active = true;
	write_unlock_irq(&gpc->lock);
	}
	return __kvm_gpc_refresh(gpc, gpa, uhva, len);
	}

	int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
	{
	return __kvm_gpc_activate(gpc, gpa, KVM_HVA_ERR_BAD, len);
	}

	int kvm_gpc_activate_hva(struct gfn_to_pfn_cache *gpc, unsigned long uhva, unsigned long len)
	{
	return __kvm_gpc_activate(gpc, INVALID_GPA, uhva, len);
	}

	void kvm_gpc_deactivate(struct gfn_to_pfn_cache *gpc)
	{
	struct kvm *kvm = gpc->kvm;
	kvm_pfn_t old_pfn;
	void *old_khva;

	guard(mutex)(&gpc->refresh_lock);

	if (gpc->active) {
	/*
	* Deactivate the cache before removing it from the list, KVM
	* must stall mmu_notifier events until all users go away, i.e.
	* until gpc->lock is dropped and refresh is guaranteed to fail.
	*/
	write_lock_irq(&gpc->lock);
	gpc->active = false;
	gpc->valid = false;

	/*
	* Leave the GPA => uHVA cache intact, it's protected by the
	* memslot generation. The PFN lookup needs to be redone every
	* time as mmu_notifier protection is lost when the cache is
	* removed from the VM's gpc_list.
	*/
	old_khva = gpc->khva - offset_in_page(gpc->khva);
	gpc->khva = NULL;

	old_pfn = gpc->pfn;
	gpc->pfn = KVM_PFN_ERR_FAULT;
	write_unlock_irq(&gpc->lock);

	spin_lock(&kvm->gpc_lock);
	list_del(&gpc->list);
	spin_unlock(&kvm->gpc_lock);

	gpc_unmap(old_pfn, old_khva);
	}
	}