arch/powerpc/kvm/book3s_64_vio_hv.c - linux - Git at Google

 /*
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License, version 2, as
  * published by the Free Software Foundation.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
  *
  * Copyright 2010 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
  * Copyright 2011 David Gibson, IBM Corporation <dwg@au1.ibm.com>
  * Copyright 2016 Alexey Kardashevskiy, IBM Corporation <aik@au1.ibm.com>
  */

 #include <linux/types.h>
 #include <linux/string.h>
 #include <linux/kvm.h>
 #include <linux/kvm_host.h>
 #include <linux/highmem.h>
 #include <linux/gfp.h>
 #include <linux/slab.h>
 #include <linux/hugetlb.h>
 #include <linux/list.h>

 #include <asm/tlbflush.h>
 #include <asm/kvm_ppc.h>
 #include <asm/kvm_book3s.h>
 #include <asm/mmu-hash64.h>
 #include <asm/mmu_context.h>
 #include <asm/hvcall.h>
 #include <asm/synch.h>
 #include <asm/ppc-opcode.h>
 #include <asm/kvm_host.h>
 #include <asm/udbg.h>
 #include <asm/iommu.h>
 #include <asm/tce.h>
 #include <asm/iommu.h>

 #define TCES_PER_PAGE	(PAGE_SIZE / sizeof(u64))

 /*
  * Finds a TCE table descriptor by LIOBN.
  *
  * WARNING: This will be called in real or virtual mode on HV KVM and virtual
  *          mode on PR KVM
  */
 struct kvmppc_spapr_tce_table *kvmppc_find_table(struct kvm_vcpu *vcpu,
 		unsigned long liobn)
 {
 	struct kvm *kvm = vcpu->kvm;
 	struct kvmppc_spapr_tce_table *stt;

 	list_for_each_entry_lockless(stt, &kvm->arch.spapr_tce_tables, list)
 		if (stt->liobn == liobn)
 			return stt;

 	return NULL;
 }
 EXPORT_SYMBOL_GPL(kvmppc_find_table);

 /*
  * Validates IO address.
  *
  * WARNING: This will be called in real-mode on HV KVM and virtual
  *          mode on PR KVM
  */
 long kvmppc_ioba_validate(struct kvmppc_spapr_tce_table *stt,
 		unsigned long ioba, unsigned long npages)
 {
 	unsigned long mask = (1ULL << stt->page_shift) - 1;
 	unsigned long idx = ioba >> stt->page_shift;

 	if ((ioba & mask) || (idx < stt->offset) ||
 			(idx - stt->offset + npages > stt->size) ||
 			(idx + npages < idx))
 		return H_PARAMETER;

 	return H_SUCCESS;
 }
 EXPORT_SYMBOL_GPL(kvmppc_ioba_validate);

 /*
  * Validates TCE address.
  * At the moment flags and page mask are validated.
  * As the host kernel does not access those addresses (just puts them
  * to the table and user space is supposed to process them), we can skip
  * checking other things (such as TCE is a guest RAM address or the page
  * was actually allocated).
  *
  * WARNING: This will be called in real-mode on HV KVM and virtual
  *          mode on PR KVM
  */
 long kvmppc_tce_validate(struct kvmppc_spapr_tce_table *stt, unsigned long tce)
 {
 	unsigned long page_mask = ~((1ULL << stt->page_shift) - 1);
 	unsigned long mask = ~(page_mask | TCE_PCI_WRITE | TCE_PCI_READ);

 	if (tce & mask)
 		return H_PARAMETER;

 	return H_SUCCESS;
 }
 EXPORT_SYMBOL_GPL(kvmppc_tce_validate);

 /* Note on the use of page_address() in real mode,
  *
  * It is safe to use page_address() in real mode on ppc64 because
  * page_address() is always defined as lowmem_page_address()
  * which returns __va(PFN_PHYS(page_to_pfn(page))) which is arithmetic
  * operation and does not access page struct.
  *
  * Theoretically page_address() could be defined different
  * but either WANT_PAGE_VIRTUAL or HASHED_PAGE_VIRTUAL
  * would have to be enabled.
  * WANT_PAGE_VIRTUAL is never enabled on ppc32/ppc64,
  * HASHED_PAGE_VIRTUAL could be enabled for ppc32 only and only
  * if CONFIG_HIGHMEM is defined. As CONFIG_SPARSEMEM_VMEMMAP
  * is not expected to be enabled on ppc32, page_address()
  * is safe for ppc32 as well.
  *
  * WARNING: This will be called in real-mode on HV KVM and virtual
  *          mode on PR KVM
  */
 static u64 *kvmppc_page_address(struct page *page)
 {
 #if defined(HASHED_PAGE_VIRTUAL) || defined(WANT_PAGE_VIRTUAL)
 #error TODO: fix to avoid page_address() here
 #endif
 	return (u64 *) page_address(page);
 }

 /*
  * Handles TCE requests for emulated devices.
  * Puts guest TCE values to the table and expects user space to convert them.
  * Called in both real and virtual modes.
  * Cannot fail so kvmppc_tce_validate must be called before it.
  *
  * WARNING: This will be called in real-mode on HV KVM and virtual
  *          mode on PR KVM
  */
 void kvmppc_tce_put(struct kvmppc_spapr_tce_table *stt,
 		unsigned long idx, unsigned long tce)
 {
 	struct page *page;
 	u64 *tbl;

 	idx -= stt->offset;
 	page = stt->pages[idx / TCES_PER_PAGE];
 	tbl = kvmppc_page_address(page);

 	tbl[idx % TCES_PER_PAGE] = tce;
 }
 EXPORT_SYMBOL_GPL(kvmppc_tce_put);

 long kvmppc_gpa_to_ua(struct kvm *kvm, unsigned long gpa,
 		unsigned long *ua, unsigned long **prmap)
 {
 	unsigned long gfn = gpa >> PAGE_SHIFT;
 	struct kvm_memory_slot *memslot;

 	memslot = search_memslots(kvm_memslots(kvm), gfn);
 	if (!memslot)
 		return -EINVAL;

 	*ua = __gfn_to_hva_memslot(memslot, gfn) |
 		(gpa & ~(PAGE_MASK | TCE_PCI_READ | TCE_PCI_WRITE));

 #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
 	if (prmap)
 		*prmap = &memslot->arch.rmap[gfn - memslot->base_gfn];
 #endif

 	return 0;
 }
 EXPORT_SYMBOL_GPL(kvmppc_gpa_to_ua);

 #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
 long kvmppc_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
 		      unsigned long ioba, unsigned long tce)
 {
 	struct kvmppc_spapr_tce_table *stt = kvmppc_find_table(vcpu, liobn);
 	long ret;

 	/* udbg_printf("H_PUT_TCE(): liobn=0x%lx ioba=0x%lx, tce=0x%lx\n", */
 	/* 	    liobn, ioba, tce); */

 	if (!stt)
 		return H_TOO_HARD;

 	ret = kvmppc_ioba_validate(stt, ioba, 1);
 	if (ret != H_SUCCESS)
 		return ret;

 	ret = kvmppc_tce_validate(stt, tce);
 	if (ret != H_SUCCESS)
 		return ret;

 	kvmppc_tce_put(stt, ioba >> stt->page_shift, tce);

 	return H_SUCCESS;
 }
 EXPORT_SYMBOL_GPL(kvmppc_h_put_tce);

 static long kvmppc_rm_ua_to_hpa(struct kvm_vcpu *vcpu,
 		unsigned long ua, unsigned long *phpa)
 {
 	pte_t *ptep, pte;
 	unsigned shift = 0;

 	ptep = __find_linux_pte_or_hugepte(vcpu->arch.pgdir, ua, NULL, &shift);
 	if (!ptep || !pte_present(*ptep))
 		return -ENXIO;
 	pte = *ptep;

 	if (!shift)
 		shift = PAGE_SHIFT;

 	/* Avoid handling anything potentially complicated in realmode */
 	if (shift > PAGE_SHIFT)
 		return -EAGAIN;

 	if (!pte_young(pte))
 		return -EAGAIN;

 	*phpa = (pte_pfn(pte) << PAGE_SHIFT) | (ua & ((1ULL << shift) - 1)) |
 			(ua & ~PAGE_MASK);

 	return 0;
 }

 long kvmppc_rm_h_put_tce_indirect(struct kvm_vcpu *vcpu,
 		unsigned long liobn, unsigned long ioba,
 		unsigned long tce_list,	unsigned long npages)
 {
 	struct kvmppc_spapr_tce_table *stt;
 	long i, ret = H_SUCCESS;
 	unsigned long tces, entry, ua = 0;
 	unsigned long *rmap = NULL;

 	stt = kvmppc_find_table(vcpu, liobn);
 	if (!stt)
 		return H_TOO_HARD;

 	entry = ioba >> stt->page_shift;
 	/*
 	 * The spec says that the maximum size of the list is 512 TCEs
 	 * so the whole table addressed resides in 4K page
 	 */
 	if (npages > 512)
 		return H_PARAMETER;

 	if (tce_list & (SZ_4K - 1))
 		return H_PARAMETER;

 	ret = kvmppc_ioba_validate(stt, ioba, npages);
 	if (ret != H_SUCCESS)
 		return ret;

 	if (kvmppc_gpa_to_ua(vcpu->kvm, tce_list, &ua, &rmap))
 		return H_TOO_HARD;

 	rmap = (void *) vmalloc_to_phys(rmap);

 	/*
 	 * Synchronize with the MMU notifier callbacks in
 	 * book3s_64_mmu_hv.c (kvm_unmap_hva_hv etc.).
 	 * While we have the rmap lock, code running on other CPUs
 	 * cannot finish unmapping the host real page that backs
 	 * this guest real page, so we are OK to access the host
 	 * real page.
 	 */
 	lock_rmap(rmap);
 	if (kvmppc_rm_ua_to_hpa(vcpu, ua, &tces)) {
 		ret = H_TOO_HARD;
 		goto unlock_exit;
 	}

 	for (i = 0; i < npages; ++i) {
 		unsigned long tce = be64_to_cpu(((u64 *)tces)[i]);

 		ret = kvmppc_tce_validate(stt, tce);
 		if (ret != H_SUCCESS)
 			goto unlock_exit;

 		kvmppc_tce_put(stt, entry + i, tce);
 	}

 unlock_exit:
 	unlock_rmap(rmap);

 	return ret;
 }

 long kvmppc_h_stuff_tce(struct kvm_vcpu *vcpu,
 		unsigned long liobn, unsigned long ioba,
 		unsigned long tce_value, unsigned long npages)
 {
 	struct kvmppc_spapr_tce_table *stt;
 	long i, ret;

 	stt = kvmppc_find_table(vcpu, liobn);
 	if (!stt)
 		return H_TOO_HARD;

 	ret = kvmppc_ioba_validate(stt, ioba, npages);
 	if (ret != H_SUCCESS)
 		return ret;

 	/* Check permission bits only to allow userspace poison TCE for debug */
 	if (tce_value & (TCE_PCI_WRITE | TCE_PCI_READ))
 		return H_PARAMETER;

 	for (i = 0; i < npages; ++i, ioba += (1ULL << stt->page_shift))
 		kvmppc_tce_put(stt, ioba >> stt->page_shift, tce_value);

 	return H_SUCCESS;
 }
 EXPORT_SYMBOL_GPL(kvmppc_h_stuff_tce);

 long kvmppc_h_get_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
 		      unsigned long ioba)
 {
 	struct kvmppc_spapr_tce_table *stt = kvmppc_find_table(vcpu, liobn);
 	long ret;
 	unsigned long idx;
 	struct page *page;
 	u64 *tbl;

 	if (!stt)
 		return H_TOO_HARD;

 	ret = kvmppc_ioba_validate(stt, ioba, 1);
 	if (ret != H_SUCCESS)
 		return ret;

 	idx = (ioba >> stt->page_shift) - stt->offset;
 	page = stt->pages[idx / TCES_PER_PAGE];
 	tbl = (u64 *)page_address(page);

 	vcpu->arch.gpr[4] = tbl[idx % TCES_PER_PAGE];

 	return H_SUCCESS;
 }
 EXPORT_SYMBOL_GPL(kvmppc_h_get_tce);

 #endif /* KVM_BOOK3S_HV_POSSIBLE */
	/*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License, version 2, as
	* published by the Free Software Foundation.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program; if not, write to the Free Software
	* Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
	*
	* Copyright 2010 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
	* Copyright 2011 David Gibson, IBM Corporation <dwg@au1.ibm.com>
	* Copyright 2016 Alexey Kardashevskiy, IBM Corporation <aik@au1.ibm.com>
	*/

	#include <linux/types.h>
	#include <linux/string.h>
	#include <linux/kvm.h>
	#include <linux/kvm_host.h>
	#include <linux/highmem.h>
	#include <linux/gfp.h>
	#include <linux/slab.h>
	#include <linux/hugetlb.h>
	#include <linux/list.h>

	#include <asm/tlbflush.h>
	#include <asm/kvm_ppc.h>
	#include <asm/kvm_book3s.h>
	#include <asm/mmu-hash64.h>
	#include <asm/mmu_context.h>
	#include <asm/hvcall.h>
	#include <asm/synch.h>
	#include <asm/ppc-opcode.h>
	#include <asm/kvm_host.h>
	#include <asm/udbg.h>
	#include <asm/iommu.h>
	#include <asm/tce.h>
	#include <asm/iommu.h>

	#define TCES_PER_PAGE (PAGE_SIZE / sizeof(u64))

	/*
	* Finds a TCE table descriptor by LIOBN.
	*
	* WARNING: This will be called in real or virtual mode on HV KVM and virtual
	* mode on PR KVM
	*/
	struct kvmppc_spapr_tce_table kvmppc_find_table(struct kvm_vcpu vcpu,
	unsigned long liobn)
	{
	struct kvm *kvm = vcpu->kvm;
	struct kvmppc_spapr_tce_table *stt;

	list_for_each_entry_lockless(stt, &kvm->arch.spapr_tce_tables, list)
	if (stt->liobn == liobn)
	return stt;

	return NULL;
	}
	EXPORT_SYMBOL_GPL(kvmppc_find_table);

	/*
	* Validates IO address.
	*
	* WARNING: This will be called in real-mode on HV KVM and virtual
	* mode on PR KVM
	*/
	long kvmppc_ioba_validate(struct kvmppc_spapr_tce_table *stt,
	unsigned long ioba, unsigned long npages)
	{
	unsigned long mask = (1ULL << stt->page_shift) - 1;
	unsigned long idx = ioba >> stt->page_shift;

	if ((ioba & mask) \|\| (idx < stt->offset) \|\|
	(idx - stt->offset + npages > stt->size) \|\|
	(idx + npages < idx))
	return H_PARAMETER;

	return H_SUCCESS;
	}
	EXPORT_SYMBOL_GPL(kvmppc_ioba_validate);

	/*
	* Validates TCE address.
	* At the moment flags and page mask are validated.
	* As the host kernel does not access those addresses (just puts them
	* to the table and user space is supposed to process them), we can skip
	* checking other things (such as TCE is a guest RAM address or the page
	* was actually allocated).
	*
	* WARNING: This will be called in real-mode on HV KVM and virtual
	* mode on PR KVM
	*/
	long kvmppc_tce_validate(struct kvmppc_spapr_tce_table *stt, unsigned long tce)
	{
	unsigned long page_mask = ~((1ULL << stt->page_shift) - 1);
	unsigned long mask = ~(page_mask \| TCE_PCI_WRITE \| TCE_PCI_READ);

	if (tce & mask)
	return H_PARAMETER;

	return H_SUCCESS;
	}
	EXPORT_SYMBOL_GPL(kvmppc_tce_validate);

	/* Note on the use of page_address() in real mode,
	*
	* It is safe to use page_address() in real mode on ppc64 because
	* page_address() is always defined as lowmem_page_address()
	* which returns __va(PFN_PHYS(page_to_pfn(page))) which is arithmetic
	* operation and does not access page struct.
	*
	* Theoretically page_address() could be defined different
	* but either WANT_PAGE_VIRTUAL or HASHED_PAGE_VIRTUAL
	* would have to be enabled.
	* WANT_PAGE_VIRTUAL is never enabled on ppc32/ppc64,
	* HASHED_PAGE_VIRTUAL could be enabled for ppc32 only and only
	* if CONFIG_HIGHMEM is defined. As CONFIG_SPARSEMEM_VMEMMAP
	* is not expected to be enabled on ppc32, page_address()
	* is safe for ppc32 as well.
	*
	* WARNING: This will be called in real-mode on HV KVM and virtual
	* mode on PR KVM
	*/
	static u64 kvmppc_page_address(struct page page)
	{
	#if defined(HASHED_PAGE_VIRTUAL) \|\| defined(WANT_PAGE_VIRTUAL)
	#error TODO: fix to avoid page_address() here
	#endif
	return (u64 *) page_address(page);
	}

	/*
	* Handles TCE requests for emulated devices.
	* Puts guest TCE values to the table and expects user space to convert them.
	* Called in both real and virtual modes.
	* Cannot fail so kvmppc_tce_validate must be called before it.
	*
	* WARNING: This will be called in real-mode on HV KVM and virtual
	* mode on PR KVM
	*/
	void kvmppc_tce_put(struct kvmppc_spapr_tce_table *stt,
	unsigned long idx, unsigned long tce)
	{
	struct page *page;
	u64 *tbl;

	idx -= stt->offset;
	page = stt->pages[idx / TCES_PER_PAGE];
	tbl = kvmppc_page_address(page);

	tbl[idx % TCES_PER_PAGE] = tce;
	}
	EXPORT_SYMBOL_GPL(kvmppc_tce_put);

	long kvmppc_gpa_to_ua(struct kvm *kvm, unsigned long gpa,
	unsigned long ua, unsigned long *prmap)
	{
	unsigned long gfn = gpa >> PAGE_SHIFT;
	struct kvm_memory_slot *memslot;

	memslot = search_memslots(kvm_memslots(kvm), gfn);
	if (!memslot)
	return -EINVAL;

	*ua = __gfn_to_hva_memslot(memslot, gfn) \|
	(gpa & ~(PAGE_MASK \| TCE_PCI_READ \| TCE_PCI_WRITE));

	#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
	if (prmap)
	*prmap = &memslot->arch.rmap[gfn - memslot->base_gfn];
	#endif

	return 0;
	}
	EXPORT_SYMBOL_GPL(kvmppc_gpa_to_ua);

	#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
	long kvmppc_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
	unsigned long ioba, unsigned long tce)
	{
	struct kvmppc_spapr_tce_table *stt = kvmppc_find_table(vcpu, liobn);
	long ret;

	/* udbg_printf("H_PUT_TCE(): liobn=0x%lx ioba=0x%lx, tce=0x%lx\n", */
	/* liobn, ioba, tce); */

	if (!stt)
	return H_TOO_HARD;

	ret = kvmppc_ioba_validate(stt, ioba, 1);
	if (ret != H_SUCCESS)
	return ret;

	ret = kvmppc_tce_validate(stt, tce);
	if (ret != H_SUCCESS)
	return ret;

	kvmppc_tce_put(stt, ioba >> stt->page_shift, tce);

	return H_SUCCESS;
	}
	EXPORT_SYMBOL_GPL(kvmppc_h_put_tce);

	static long kvmppc_rm_ua_to_hpa(struct kvm_vcpu *vcpu,
	unsigned long ua, unsigned long *phpa)
	{
	pte_t *ptep, pte;
	unsigned shift = 0;

	ptep = __find_linux_pte_or_hugepte(vcpu->arch.pgdir, ua, NULL, &shift);
	if (!ptep \|\| !pte_present(*ptep))
	return -ENXIO;
	pte = *ptep;

	if (!shift)
	shift = PAGE_SHIFT;

	/* Avoid handling anything potentially complicated in realmode */
	if (shift > PAGE_SHIFT)
	return -EAGAIN;

	if (!pte_young(pte))
	return -EAGAIN;

	*phpa = (pte_pfn(pte) << PAGE_SHIFT) \| (ua & ((1ULL << shift) - 1)) \|
	(ua & ~PAGE_MASK);

	return 0;
	}

	long kvmppc_rm_h_put_tce_indirect(struct kvm_vcpu *vcpu,
	unsigned long liobn, unsigned long ioba,
	unsigned long tce_list, unsigned long npages)
	{
	struct kvmppc_spapr_tce_table *stt;
	long i, ret = H_SUCCESS;
	unsigned long tces, entry, ua = 0;
	unsigned long *rmap = NULL;

	stt = kvmppc_find_table(vcpu, liobn);
	if (!stt)
	return H_TOO_HARD;

	entry = ioba >> stt->page_shift;
	/*
	* The spec says that the maximum size of the list is 512 TCEs
	* so the whole table addressed resides in 4K page
	*/
	if (npages > 512)
	return H_PARAMETER;

	if (tce_list & (SZ_4K - 1))
	return H_PARAMETER;

	ret = kvmppc_ioba_validate(stt, ioba, npages);
	if (ret != H_SUCCESS)
	return ret;

	if (kvmppc_gpa_to_ua(vcpu->kvm, tce_list, &ua, &rmap))
	return H_TOO_HARD;

	rmap = (void *) vmalloc_to_phys(rmap);

	/*
	* Synchronize with the MMU notifier callbacks in
	* book3s_64_mmu_hv.c (kvm_unmap_hva_hv etc.).
	* While we have the rmap lock, code running on other CPUs
	* cannot finish unmapping the host real page that backs
	* this guest real page, so we are OK to access the host
	* real page.
	*/
	lock_rmap(rmap);
	if (kvmppc_rm_ua_to_hpa(vcpu, ua, &tces)) {
	ret = H_TOO_HARD;
	goto unlock_exit;
	}

	for (i = 0; i < npages; ++i) {
	unsigned long tce = be64_to_cpu(((u64 *)tces)[i]);

	ret = kvmppc_tce_validate(stt, tce);
	if (ret != H_SUCCESS)
	goto unlock_exit;

	kvmppc_tce_put(stt, entry + i, tce);
	}

	unlock_exit:
	unlock_rmap(rmap);

	return ret;
	}

	long kvmppc_h_stuff_tce(struct kvm_vcpu *vcpu,
	unsigned long liobn, unsigned long ioba,
	unsigned long tce_value, unsigned long npages)
	{
	struct kvmppc_spapr_tce_table *stt;
	long i, ret;

	stt = kvmppc_find_table(vcpu, liobn);
	if (!stt)
	return H_TOO_HARD;

	ret = kvmppc_ioba_validate(stt, ioba, npages);
	if (ret != H_SUCCESS)
	return ret;

	/* Check permission bits only to allow userspace poison TCE for debug */
	if (tce_value & (TCE_PCI_WRITE \| TCE_PCI_READ))
	return H_PARAMETER;

	for (i = 0; i < npages; ++i, ioba += (1ULL << stt->page_shift))
	kvmppc_tce_put(stt, ioba >> stt->page_shift, tce_value);

	return H_SUCCESS;
	}
	EXPORT_SYMBOL_GPL(kvmppc_h_stuff_tce);

	long kvmppc_h_get_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
	unsigned long ioba)
	{
	struct kvmppc_spapr_tce_table *stt = kvmppc_find_table(vcpu, liobn);
	long ret;
	unsigned long idx;
	struct page *page;
	u64 *tbl;

	if (!stt)
	return H_TOO_HARD;

	ret = kvmppc_ioba_validate(stt, ioba, 1);
	if (ret != H_SUCCESS)
	return ret;

	idx = (ioba >> stt->page_shift) - stt->offset;
	page = stt->pages[idx / TCES_PER_PAGE];
	tbl = (u64 *)page_address(page);

	vcpu->arch.gpr[4] = tbl[idx % TCES_PER_PAGE];

	return H_SUCCESS;
	}
	EXPORT_SYMBOL_GPL(kvmppc_h_get_tce);

	#endif /* KVM_BOOK3S_HV_POSSIBLE */