diff mbox series

[v4,1/6] kvmppc: HMM backend driver to manage pages of secure guest

Message ID 20190528064933.23119-2-bharata@linux.ibm.com
State Superseded
Headers show
Series kvmppc: HMM driver to manage pages of secure guest | expand

Commit Message

Bharata B Rao May 28, 2019, 6:49 a.m. UTC 
HMM driver for KVM PPC to manage page transitions of
secure guest via H_SVM_PAGE_IN and H_SVM_PAGE_OUT hcalls.

H_SVM_PAGE_IN: Move the content of a normal page to secure page
H_SVM_PAGE_OUT: Move the content of a secure page to normal page

Signed-off-by: Bharata B Rao <bharata@linux.ibm.com>
---
 arch/powerpc/include/asm/hvcall.h         |   4 +
 arch/powerpc/include/asm/kvm_book3s_hmm.h |  29 ++
 arch/powerpc/include/asm/kvm_host.h       |  14 +
 arch/powerpc/include/asm/ultravisor-api.h |   2 +
 arch/powerpc/include/asm/ultravisor.h     |  17 +
 arch/powerpc/kvm/Makefile                 |   3 +
 arch/powerpc/kvm/book3s_hv.c              |  20 +
 arch/powerpc/kvm/book3s_hv_hmm.c          | 474 ++++++++++++++++++++++
 8 files changed, 563 insertions(+)
 create mode 100644 arch/powerpc/include/asm/kvm_book3s_hmm.h
 create mode 100644 arch/powerpc/kvm/book3s_hv_hmm.c

Comments

Paul Mackerras June 17, 2019, 5:31 a.m. UTC | #1 
On Tue, May 28, 2019 at 12:19:28PM +0530, Bharata B Rao wrote:
> HMM driver for KVM PPC to manage page transitions of
> secure guest via H_SVM_PAGE_IN and H_SVM_PAGE_OUT hcalls.
> 
> H_SVM_PAGE_IN: Move the content of a normal page to secure page
> H_SVM_PAGE_OUT: Move the content of a secure page to normal page

Comments below...

> @@ -4421,6 +4435,7 @@ static void kvmppc_core_free_memslot_hv(struct kvm_memory_slot *free,
>  					struct kvm_memory_slot *dont)
>  {
>  	if (!dont || free->arch.rmap != dont->arch.rmap) {
> +		kvmppc_hmm_release_pfns(free);

I don't think this is the right place to do this.  The memslot will
have no pages mapped by this time, because higher levels of code will
have called kvmppc_core_flush_memslot_hv() before calling this.
Releasing the pfns should be done in that function.

> diff --git a/arch/powerpc/kvm/book3s_hv_hmm.c b/arch/powerpc/kvm/book3s_hv_hmm.c
> new file mode 100644
> index 000000000000..713806003da3

...

> +#define KVMPPC_PFN_HMM		(0x1ULL << 61)
> +
> +static inline bool kvmppc_is_hmm_pfn(unsigned long pfn)
> +{
> +	return !!(pfn & KVMPPC_PFN_HMM);
> +}

Since you are putting in these values in the rmap entries, you need to
be careful about overlaps between these values and the other uses of
rmap entries.  The value you have chosen would be in the middle of the
LPID field for an rmap entry for a guest that has nested guests, and
in fact kvmhv_remove_nest_rmap_range() effectively assumes that a
non-zero rmap entry must be a list of L2 guest mappings.  (This is for
radix guests; HPT guests use the rmap entry differently, but I am
assuming that we will enforce that only radix guests can be secure
guests.)

Maybe it is true that the rmap entry will be non-zero only for those
guest pages which are not mapped on the host side, that is,
kvmppc_radix_flush_memslot() will see !pte_present(*ptep) for any page
of a secure guest where the rmap entry contains a HMM pfn.  If that is
so and is a deliberate part of the design, then I would like to see it
written down in comments and commit messages so it's clear to others
working on the code in future.

Suraj is working on support for nested HPT guests, which will involve
changing the rmap format to indicate more explicitly what sort of
entry each rmap entry is.  Please work with him to define a format for
your rmap entries that is clearly distinguishable from the others.

I think it is reasonable to say that a secure guest can't have nested
guests, at least for now, but then we should make sure to kill all
nested guests when a guest goes secure.

...

> +/*
> + * Move page from normal memory to secure memory.
> + */
> +unsigned long
> +kvmppc_h_svm_page_in(struct kvm *kvm, unsigned long gpa,
> +		     unsigned long flags, unsigned long page_shift)
> +{
> +	unsigned long addr, end;
> +	unsigned long src_pfn, dst_pfn;
> +	struct kvmppc_hmm_migrate_args args;
> +	struct vm_area_struct *vma;
> +	int srcu_idx;
> +	unsigned long gfn = gpa >> page_shift;
> +	struct kvm_memory_slot *slot;
> +	unsigned long *rmap;
> +	int ret = H_SUCCESS;
> +
> +	if (page_shift != PAGE_SHIFT)
> +		return H_P3;
> +
> +	srcu_idx = srcu_read_lock(&kvm->srcu);
> +	slot = gfn_to_memslot(kvm, gfn);
> +	rmap = &slot->arch.rmap[gfn - slot->base_gfn];
> +	addr = gfn_to_hva(kvm, gpa >> page_shift);
> +	srcu_read_unlock(&kvm->srcu, srcu_idx);

Shouldn't we keep the srcu read lock until we have finished working on
the page?

> +	if (kvm_is_error_hva(addr))
> +		return H_PARAMETER;
> +
> +	end = addr + (1UL << page_shift);
> +
> +	if (flags)
> +		return H_P2;
> +
> +	args.rmap = rmap;
> +	args.lpid = kvm->arch.lpid;
> +	args.gpa = gpa;
> +	args.page_shift = page_shift;
> +
> +	down_read(&kvm->mm->mmap_sem);
> +	vma = find_vma_intersection(kvm->mm, addr, end);
> +	if (!vma || vma->vm_start > addr || vma->vm_end < end) {
> +		ret = H_PARAMETER;
> +		goto out;
> +	}
> +	ret = migrate_vma(&kvmppc_hmm_migrate_ops, vma, addr, end,
> +			  &src_pfn, &dst_pfn, &args);
> +	if (ret < 0)
> +		ret = H_PARAMETER;
> +out:
> +	up_read(&kvm->mm->mmap_sem);
> +	return ret;
> +}

...

> +/*
> + * Move page from secure memory to normal memory.
> + */
> +unsigned long
> +kvmppc_h_svm_page_out(struct kvm *kvm, unsigned long gpa,
> +		      unsigned long flags, unsigned long page_shift)
> +{
> +	unsigned long addr, end;
> +	struct vm_area_struct *vma;
> +	unsigned long src_pfn, dst_pfn = 0;
> +	int srcu_idx;
> +	int ret = H_SUCCESS;
> +
> +	if (page_shift != PAGE_SHIFT)
> +		return H_P3;
> +
> +	if (flags)
> +		return H_P2;
> +
> +	srcu_idx = srcu_read_lock(&kvm->srcu);
> +	addr = gfn_to_hva(kvm, gpa >> page_shift);
> +	srcu_read_unlock(&kvm->srcu, srcu_idx);

and likewise here, shouldn't we unlock later, after the migrate_vma()
call perhaps?

> +	if (kvm_is_error_hva(addr))
> +		return H_PARAMETER;
> +
> +	end = addr + (1UL << page_shift);
> +
> +	down_read(&kvm->mm->mmap_sem);
> +	vma = find_vma_intersection(kvm->mm, addr, end);
> +	if (!vma || vma->vm_start > addr || vma->vm_end < end) {
> +		ret = H_PARAMETER;
> +		goto out;
> +	}
> +	ret = migrate_vma(&kvmppc_hmm_fault_migrate_ops, vma, addr, end,
> +			  &src_pfn, &dst_pfn, NULL);
> +	if (ret < 0)
> +		ret = H_PARAMETER;
> +out:
> +	up_read(&kvm->mm->mmap_sem);
> +	return ret;
> +}
> +

Paul.
Bharata B Rao July 9, 2019, 10:03 a.m. UTC | #2 
On Mon, Jun 17, 2019 at 03:31:06PM +1000, Paul Mackerras wrote:
> On Tue, May 28, 2019 at 12:19:28PM +0530, Bharata B Rao wrote:
> > HMM driver for KVM PPC to manage page transitions of
> > secure guest via H_SVM_PAGE_IN and H_SVM_PAGE_OUT hcalls.
> > 
> > H_SVM_PAGE_IN: Move the content of a normal page to secure page
> > H_SVM_PAGE_OUT: Move the content of a secure page to normal page
> 
> Comments below...
> 
> > @@ -4421,6 +4435,7 @@ static void kvmppc_core_free_memslot_hv(struct kvm_memory_slot *free,
> >  					struct kvm_memory_slot *dont)
> >  {
> >  	if (!dont || free->arch.rmap != dont->arch.rmap) {
> > +		kvmppc_hmm_release_pfns(free);
> 
> I don't think this is the right place to do this.  The memslot will
> have no pages mapped by this time, because higher levels of code will
> have called kvmppc_core_flush_memslot_hv() before calling this.
> Releasing the pfns should be done in that function.

In fact I can get rid of kvmppc_hmm_release_pfns() totally as we don't
have to do free the HMM pages like this explicitly. During guest shutdown
all these pages are dropped when unmap_vmas() is called.

> 
> > diff --git a/arch/powerpc/kvm/book3s_hv_hmm.c b/arch/powerpc/kvm/book3s_hv_hmm.c
> > new file mode 100644
> > index 000000000000..713806003da3
> 
> ...
> 
> > +#define KVMPPC_PFN_HMM		(0x1ULL << 61)
> > +
> > +static inline bool kvmppc_is_hmm_pfn(unsigned long pfn)
> > +{
> > +	return !!(pfn & KVMPPC_PFN_HMM);
> > +}
> 
> Since you are putting in these values in the rmap entries, you need to
> be careful about overlaps between these values and the other uses of
> rmap entries.  The value you have chosen would be in the middle of the
> LPID field for an rmap entry for a guest that has nested guests, and
> in fact kvmhv_remove_nest_rmap_range() effectively assumes that a
> non-zero rmap entry must be a list of L2 guest mappings.  (This is for
> radix guests; HPT guests use the rmap entry differently, but I am
> assuming that we will enforce that only radix guests can be secure
> guests.)

Worked out with Suraj on sharing the rmap and got a well defined
bit slot for HMM PFNs in rmap.

> 
> Maybe it is true that the rmap entry will be non-zero only for those
> guest pages which are not mapped on the host side, that is,
> kvmppc_radix_flush_memslot() will see !pte_present(*ptep) for any page
> of a secure guest where the rmap entry contains a HMM pfn.  If that is
> so and is a deliberate part of the design, then I would like to see it
> written down in comments and commit messages so it's clear to others
> working on the code in future.

Yes, rmap entry will be non-zero only for those guest pages which are
not mapped on the host side. However as soon as guest becomes secure
we free the HV side partition scoped page tables and hence
kvmppc_radix_flush_memslot() and other such routines which lookup
kvm->arch.pgtable will no longer touch it.

> 
> Suraj is working on support for nested HPT guests, which will involve
> changing the rmap format to indicate more explicitly what sort of
> entry each rmap entry is.  Please work with him to define a format for
> your rmap entries that is clearly distinguishable from the others.
> 
> I think it is reasonable to say that a secure guest can't have nested
> guests, at least for now, but then we should make sure to kill all
> nested guests when a guest goes secure.

Ok. Yet to figure this part out.

> 
> ...
> 
> > +/*
> > + * Move page from normal memory to secure memory.
> > + */
> > +unsigned long
> > +kvmppc_h_svm_page_in(struct kvm *kvm, unsigned long gpa,
> > +		     unsigned long flags, unsigned long page_shift)
> > +{
> > +	unsigned long addr, end;
> > +	unsigned long src_pfn, dst_pfn;
> > +	struct kvmppc_hmm_migrate_args args;
> > +	struct vm_area_struct *vma;
> > +	int srcu_idx;
> > +	unsigned long gfn = gpa >> page_shift;
> > +	struct kvm_memory_slot *slot;
> > +	unsigned long *rmap;
> > +	int ret = H_SUCCESS;
> > +
> > +	if (page_shift != PAGE_SHIFT)
> > +		return H_P3;
> > +
> > +	srcu_idx = srcu_read_lock(&kvm->srcu);
> > +	slot = gfn_to_memslot(kvm, gfn);
> > +	rmap = &slot->arch.rmap[gfn - slot->base_gfn];
> > +	addr = gfn_to_hva(kvm, gpa >> page_shift);
> > +	srcu_read_unlock(&kvm->srcu, srcu_idx);
> 
> Shouldn't we keep the srcu read lock until we have finished working on
> the page?

I wasn't sure, so keeping it locked till the end in the next version.

> 
> > +	if (kvm_is_error_hva(addr))
> > +		return H_PARAMETER;
> > +
> > +	end = addr + (1UL << page_shift);
> > +
> > +	if (flags)
> > +		return H_P2;
> > +
> > +	args.rmap = rmap;
> > +	args.lpid = kvm->arch.lpid;
> > +	args.gpa = gpa;
> > +	args.page_shift = page_shift;
> > +
> > +	down_read(&kvm->mm->mmap_sem);
> > +	vma = find_vma_intersection(kvm->mm, addr, end);
> > +	if (!vma || vma->vm_start > addr || vma->vm_end < end) {
> > +		ret = H_PARAMETER;
> > +		goto out;
> > +	}
> > +	ret = migrate_vma(&kvmppc_hmm_migrate_ops, vma, addr, end,
> > +			  &src_pfn, &dst_pfn, &args);
> > +	if (ret < 0)
> > +		ret = H_PARAMETER;
> > +out:
> > +	up_read(&kvm->mm->mmap_sem);
> > +	return ret;
> > +}
> 
> ...
> 
> > +/*
> > + * Move page from secure memory to normal memory.
> > + */
> > +unsigned long
> > +kvmppc_h_svm_page_out(struct kvm *kvm, unsigned long gpa,
> > +		      unsigned long flags, unsigned long page_shift)
> > +{
> > +	unsigned long addr, end;
> > +	struct vm_area_struct *vma;
> > +	unsigned long src_pfn, dst_pfn = 0;
> > +	int srcu_idx;
> > +	int ret = H_SUCCESS;
> > +
> > +	if (page_shift != PAGE_SHIFT)
> > +		return H_P3;
> > +
> > +	if (flags)
> > +		return H_P2;
> > +
> > +	srcu_idx = srcu_read_lock(&kvm->srcu);
> > +	addr = gfn_to_hva(kvm, gpa >> page_shift);
> > +	srcu_read_unlock(&kvm->srcu, srcu_idx);
> 
> and likewise here, shouldn't we unlock later, after the migrate_vma()
> call perhaps?

Sure.

Regards,
Bharata.
diff mbox series

Patch

diff --git a/arch/powerpc/include/asm/hvcall.h b/arch/powerpc/include/asm/hvcall.h
index 463c63a9fcf1..2f6b952deb0f 100644
--- a/arch/powerpc/include/asm/hvcall.h
+++ b/arch/powerpc/include/asm/hvcall.h
@@ -337,6 +337,10 @@ 
 #define H_TLB_INVALIDATE	0xF808
 #define H_COPY_TOFROM_GUEST	0xF80C
 
+/* Platform-specific hcalls used by the Ultravisor */
+#define H_SVM_PAGE_IN		0xEF00
+#define H_SVM_PAGE_OUT		0xEF04
+
 /* Values for 2nd argument to H_SET_MODE */
 #define H_SET_MODE_RESOURCE_SET_CIABR		1
 #define H_SET_MODE_RESOURCE_SET_DAWR		2
diff --git a/arch/powerpc/include/asm/kvm_book3s_hmm.h b/arch/powerpc/include/asm/kvm_book3s_hmm.h
new file mode 100644
index 000000000000..21f3de5f2acb
--- /dev/null
+++ b/arch/powerpc/include/asm/kvm_book3s_hmm.h
@@ -0,0 +1,29 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __POWERPC_KVM_PPC_HMM_H__
+#define __POWERPC_KVM_PPC_HMM_H__
+
+#ifdef CONFIG_PPC_UV
+extern unsigned long kvmppc_h_svm_page_in(struct kvm *kvm,
+					  unsigned long gra,
+					  unsigned long flags,
+					  unsigned long page_shift);
+extern unsigned long kvmppc_h_svm_page_out(struct kvm *kvm,
+					  unsigned long gra,
+					  unsigned long flags,
+					  unsigned long page_shift);
+#else
+static inline unsigned long
+kvmppc_h_svm_page_in(struct kvm *kvm, unsigned long gra,
+		     unsigned long flags, unsigned long page_shift)
+{
+	return H_UNSUPPORTED;
+}
+
+static inline unsigned long
+kvmppc_h_svm_page_out(struct kvm *kvm, unsigned long gra,
+		      unsigned long flags, unsigned long page_shift)
+{
+	return H_UNSUPPORTED;
+}
+#endif /* CONFIG_PPC_UV */
+#endif /* __POWERPC_KVM_PPC_HMM_H__ */
diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index 184becb62ea4..c0c9c3455ac4 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -858,4 +858,18 @@  static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {}
 static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {}
 static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {}
 
+#ifdef CONFIG_PPC_UV
+extern int kvmppc_hmm_init(void);
+extern void kvmppc_hmm_free(void);
+extern void kvmppc_hmm_release_pfns(struct kvm_memory_slot *free);
+#else
+static inline int kvmppc_hmm_init(void)
+{
+	return 0;
+}
+
+static inline void kvmppc_hmm_free(void) {}
+static inline void kvmppc_hmm_release_pfns(struct kvm_memory_slot *free) {}
+#endif /* CONFIG_PPC_UV */
+
 #endif /* __POWERPC_KVM_HOST_H__ */
diff --git a/arch/powerpc/include/asm/ultravisor-api.h b/arch/powerpc/include/asm/ultravisor-api.h
index 15e6ce77a131..51c4e0b5d197 100644
--- a/arch/powerpc/include/asm/ultravisor-api.h
+++ b/arch/powerpc/include/asm/ultravisor-api.h
@@ -20,5 +20,7 @@ 
 /* opcodes */
 #define UV_WRITE_PATE			0xF104
 #define UV_RETURN			0xF11C
+#define UV_PAGE_IN			0xF128
+#define UV_PAGE_OUT			0xF12C
 
 #endif /* _ASM_POWERPC_ULTRAVISOR_API_H */
diff --git a/arch/powerpc/include/asm/ultravisor.h b/arch/powerpc/include/asm/ultravisor.h
index 4ffec7a36acd..1e4c51799b43 100644
--- a/arch/powerpc/include/asm/ultravisor.h
+++ b/arch/powerpc/include/asm/ultravisor.h
@@ -44,6 +44,23 @@  static inline int uv_register_pate(u64 lpid, u64 dw0, u64 dw1)
 	return ucall(UV_WRITE_PATE, retbuf, lpid, dw0, dw1);
 }
 
+static inline int uv_page_in(u64 lpid, u64 src_ra, u64 dst_gpa, u64 flags,
+			     u64 page_shift)
+{
+	unsigned long retbuf[UCALL_BUFSIZE];
+
+	return ucall(UV_PAGE_IN, retbuf, lpid, src_ra, dst_gpa, flags,
+		     page_shift);
+}
+
+static inline int uv_page_out(u64 lpid, u64 dst_ra, u64 src_gpa, u64 flags,
+			      u64 page_shift)
+{
+	unsigned long retbuf[UCALL_BUFSIZE];
+
+	return ucall(UV_PAGE_OUT, retbuf, lpid, dst_ra, src_gpa, flags,
+		     page_shift);
+}
 #endif /* !__ASSEMBLY__ */
 
 #endif	/* _ASM_POWERPC_ULTRAVISOR_H */
diff --git a/arch/powerpc/kvm/Makefile b/arch/powerpc/kvm/Makefile
index 4c67cc79de7c..d1a79fb5f806 100644
--- a/arch/powerpc/kvm/Makefile
+++ b/arch/powerpc/kvm/Makefile
@@ -71,6 +71,9 @@  kvm-hv-y += \
 	book3s_64_mmu_radix.o \
 	book3s_hv_nested.o
 
+kvm-hv-$(CONFIG_PPC_UV) += \
+	book3s_hv_hmm.o
+
 kvm-hv-$(CONFIG_PPC_TRANSACTIONAL_MEM) += \
 	book3s_hv_tm.o
 
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 57ce45a997c7..2918616198de 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -76,6 +76,8 @@ 
 #include <asm/xive.h>
 #include <asm/hw_breakpoint.h>
 #include <asm/firmware.h>
+#include <asm/kvm_host.h>
+#include <asm/kvm_book3s_hmm.h>
 
 #include "book3s.h"
 
@@ -1084,6 +1086,18 @@  int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu)
 					 kvmppc_get_gpr(vcpu, 5),
 					 kvmppc_get_gpr(vcpu, 6));
 		break;
+	case H_SVM_PAGE_IN:
+		ret = kvmppc_h_svm_page_in(vcpu->kvm,
+					   kvmppc_get_gpr(vcpu, 4),
+					   kvmppc_get_gpr(vcpu, 5),
+					   kvmppc_get_gpr(vcpu, 6));
+		break;
+	case H_SVM_PAGE_OUT:
+		ret = kvmppc_h_svm_page_out(vcpu->kvm,
+					    kvmppc_get_gpr(vcpu, 4),
+					    kvmppc_get_gpr(vcpu, 5),
+					    kvmppc_get_gpr(vcpu, 6));
+		break;
 	default:
 		return RESUME_HOST;
 	}
@@ -4421,6 +4435,7 @@  static void kvmppc_core_free_memslot_hv(struct kvm_memory_slot *free,
 					struct kvm_memory_slot *dont)
 {
 	if (!dont || free->arch.rmap != dont->arch.rmap) {
+		kvmppc_hmm_release_pfns(free);
 		vfree(free->arch.rmap);
 		free->arch.rmap = NULL;
 	}
@@ -5494,11 +5509,16 @@  static int kvmppc_book3s_init_hv(void)
 			no_mixing_hpt_and_radix = true;
 	}
 
+	r = kvmppc_hmm_init();
+	if (r < 0)
+		pr_err("KVM-HV: kvmppc_hmm_init failed %d\n", r);
+
 	return r;
 }
 
 static void kvmppc_book3s_exit_hv(void)
 {
+	kvmppc_hmm_free();
 	kvmppc_free_host_rm_ops();
 	if (kvmppc_radix_possible())
 		kvmppc_radix_exit();
diff --git a/arch/powerpc/kvm/book3s_hv_hmm.c b/arch/powerpc/kvm/book3s_hv_hmm.c
new file mode 100644
index 000000000000..713806003da3
--- /dev/null
+++ b/arch/powerpc/kvm/book3s_hv_hmm.c
@@ -0,0 +1,474 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * HMM driver to manage page migration between normal and secure
+ * memory.
+ *
+ * Based on Jérôme Glisse's HMM dummy driver.
+ *
+ * Copyright 2018 Bharata B Rao, IBM Corp. <bharata@linux.ibm.com>
+ */
+
+/*
+ * A pseries guest can be run as a secure guest on Ultravisor-enabled
+ * POWER platforms. On such platforms, this driver will be used to manage
+ * the movement of guest pages between the normal memory managed by
+ * hypervisor (HV) and secure memory managed by Ultravisor (UV).
+ *
+ * Private ZONE_DEVICE memory equal to the amount of secure memory
+ * available in the platform for running secure guests is created
+ * via a HMM device. The movement of pages between normal and secure
+ * memory is done by ->alloc_and_copy() callback routine of migrate_vma().
+ *
+ * The page-in or page-out requests from UV will come to HV as hcalls and
+ * HV will call back into UV via uvcalls to satisfy these page requests.
+ *
+ * For each page that gets moved into secure memory, a HMM PFN is used
+ * on the HV side and HMM migration PTE corresponding to that PFN would be
+ * populated in the QEMU page tables.
+ */
+
+#include <linux/hmm.h>
+#include <linux/kvm_host.h>
+#include <linux/sched/mm.h>
+#include <asm/ultravisor.h>
+
+struct kvmppc_hmm_device {
+	struct hmm_device *device;
+	struct hmm_devmem *devmem;
+	unsigned long *pfn_bitmap;
+};
+
+static struct kvmppc_hmm_device kvmppc_hmm;
+spinlock_t kvmppc_hmm_lock;
+
+struct kvmppc_hmm_page_pvt {
+	unsigned long *rmap;
+	unsigned int lpid;
+	unsigned long gpa;
+};
+
+struct kvmppc_hmm_migrate_args {
+	unsigned long *rmap;
+	unsigned int lpid;
+	unsigned long gpa;
+	unsigned long page_shift;
+};
+
+#define KVMPPC_PFN_HMM		(0x1ULL << 61)
+
+static inline bool kvmppc_is_hmm_pfn(unsigned long pfn)
+{
+	return !!(pfn & KVMPPC_PFN_HMM);
+}
+
+void kvmppc_hmm_release_pfns(struct kvm_memory_slot *free)
+{
+	int i;
+
+	for (i = 0; i < free->npages; i++) {
+		unsigned long *rmap = &free->arch.rmap[i];
+
+		if (kvmppc_is_hmm_pfn(*rmap))
+			put_page(pfn_to_page(*rmap & ~KVMPPC_PFN_HMM));
+	}
+}
+
+/*
+ * Get a free HMM PFN from the pool
+ *
+ * Called when a normal page is moved to secure memory (UV_PAGE_IN). HMM
+ * PFN will be used to keep track of the secure page on HV side.
+ */
+/*
+ * TODO: In this and subsequent functions, we pass around and access
+ * individual elements of kvm_memory_slot->arch.rmap[] without any
+ * protection. Figure out the safe way to access this.
+ */
+static struct page *kvmppc_hmm_get_page(unsigned long *rmap,
+					unsigned long gpa, unsigned int lpid)
+{
+	struct page *dpage = NULL;
+	unsigned long bit, hmm_pfn;
+	unsigned long nr_pfns = kvmppc_hmm.devmem->pfn_last -
+				kvmppc_hmm.devmem->pfn_first;
+	unsigned long flags;
+	struct kvmppc_hmm_page_pvt *pvt;
+
+	if (kvmppc_is_hmm_pfn(*rmap))
+		return NULL;
+
+	spin_lock_irqsave(&kvmppc_hmm_lock, flags);
+	bit = find_first_zero_bit(kvmppc_hmm.pfn_bitmap, nr_pfns);
+	if (bit >= nr_pfns)
+		goto out;
+
+	bitmap_set(kvmppc_hmm.pfn_bitmap, bit, 1);
+	hmm_pfn = bit + kvmppc_hmm.devmem->pfn_first;
+	dpage = pfn_to_page(hmm_pfn);
+
+	if (!trylock_page(dpage))
+		goto out_clear;
+
+	*rmap = hmm_pfn | KVMPPC_PFN_HMM;
+	pvt = kzalloc(sizeof(*pvt), GFP_ATOMIC);
+	if (!pvt)
+		goto out_unlock;
+	pvt->rmap = rmap;
+	pvt->gpa = gpa;
+	pvt->lpid = lpid;
+	hmm_devmem_page_set_drvdata(dpage, (unsigned long)pvt);
+	spin_unlock_irqrestore(&kvmppc_hmm_lock, flags);
+
+	get_page(dpage);
+	return dpage;
+
+out_unlock:
+	unlock_page(dpage);
+out_clear:
+	bitmap_clear(kvmppc_hmm.pfn_bitmap,
+		     hmm_pfn - kvmppc_hmm.devmem->pfn_first, 1);
+out:
+	spin_unlock_irqrestore(&kvmppc_hmm_lock, flags);
+	return NULL;
+}
+
+/*
+ * Release the HMM PFN back to the pool
+ *
+ * Called when secure page becomes a normal page during UV_PAGE_OUT.
+ */
+static void kvmppc_hmm_put_page(struct page *page)
+{
+	unsigned long pfn = page_to_pfn(page);
+	unsigned long flags;
+	struct kvmppc_hmm_page_pvt *pvt;
+
+	spin_lock_irqsave(&kvmppc_hmm_lock, flags);
+	pvt = (struct kvmppc_hmm_page_pvt *)hmm_devmem_page_get_drvdata(page);
+	hmm_devmem_page_set_drvdata(page, 0);
+
+	bitmap_clear(kvmppc_hmm.pfn_bitmap,
+		     pfn - kvmppc_hmm.devmem->pfn_first, 1);
+	*(pvt->rmap) = 0;
+	spin_unlock_irqrestore(&kvmppc_hmm_lock, flags);
+	kfree(pvt);
+}
+
+/*
+ * migrate_vma() callback to move page from normal memory to secure memory.
+ *
+ * We don't capture the return value of uv_page_in() here because when
+ * UV asks for a page and then fails to copy it over, we don't care.
+ */
+static void
+kvmppc_hmm_migrate_alloc_and_copy(struct vm_area_struct *vma,
+				  const unsigned long *src_pfn,
+				  unsigned long *dst_pfn,
+				  unsigned long start,
+				  unsigned long end,
+				  void *private)
+{
+	struct kvmppc_hmm_migrate_args *args = private;
+	struct page *spage = migrate_pfn_to_page(*src_pfn);
+	unsigned long pfn = *src_pfn >> MIGRATE_PFN_SHIFT;
+	struct page *dpage;
+
+	*dst_pfn = 0;
+	if (!(*src_pfn & MIGRATE_PFN_MIGRATE))
+		return;
+
+	dpage = kvmppc_hmm_get_page(args->rmap, args->gpa, args->lpid);
+	if (!dpage)
+		return;
+
+	if (spage)
+		uv_page_in(args->lpid, pfn << args->page_shift,
+			   args->gpa, 0, args->page_shift);
+
+	*dst_pfn = migrate_pfn(page_to_pfn(dpage)) |
+		    MIGRATE_PFN_DEVICE | MIGRATE_PFN_LOCKED;
+}
+
+/*
+ * This migrate_vma() callback is typically used to updated device
+ * page tables after successful migration. We have nothing to do here.
+ *
+ * Also as we don't care if UV successfully copied over the page in
+ * kvmppc_hmm_migrate_alloc_and_copy(), we don't bother to check
+ * dst_pfn for any errors here.
+ */
+static void
+kvmppc_hmm_migrate_finalize_and_map(struct vm_area_struct *vma,
+				    const unsigned long *src_pfn,
+				    const unsigned long *dst_pfn,
+				    unsigned long start,
+				    unsigned long end,
+				    void *private)
+{
+}
+
+static const struct migrate_vma_ops kvmppc_hmm_migrate_ops = {
+	.alloc_and_copy = kvmppc_hmm_migrate_alloc_and_copy,
+	.finalize_and_map = kvmppc_hmm_migrate_finalize_and_map,
+};
+
+/*
+ * Move page from normal memory to secure memory.
+ */
+unsigned long
+kvmppc_h_svm_page_in(struct kvm *kvm, unsigned long gpa,
+		     unsigned long flags, unsigned long page_shift)
+{
+	unsigned long addr, end;
+	unsigned long src_pfn, dst_pfn;
+	struct kvmppc_hmm_migrate_args args;
+	struct vm_area_struct *vma;
+	int srcu_idx;
+	unsigned long gfn = gpa >> page_shift;
+	struct kvm_memory_slot *slot;
+	unsigned long *rmap;
+	int ret = H_SUCCESS;
+
+	if (page_shift != PAGE_SHIFT)
+		return H_P3;
+
+	srcu_idx = srcu_read_lock(&kvm->srcu);
+	slot = gfn_to_memslot(kvm, gfn);
+	rmap = &slot->arch.rmap[gfn - slot->base_gfn];
+	addr = gfn_to_hva(kvm, gpa >> page_shift);
+	srcu_read_unlock(&kvm->srcu, srcu_idx);
+	if (kvm_is_error_hva(addr))
+		return H_PARAMETER;
+
+	end = addr + (1UL << page_shift);
+
+	if (flags)
+		return H_P2;
+
+	args.rmap = rmap;
+	args.lpid = kvm->arch.lpid;
+	args.gpa = gpa;
+	args.page_shift = page_shift;
+
+	down_read(&kvm->mm->mmap_sem);
+	vma = find_vma_intersection(kvm->mm, addr, end);
+	if (!vma || vma->vm_start > addr || vma->vm_end < end) {
+		ret = H_PARAMETER;
+		goto out;
+	}
+	ret = migrate_vma(&kvmppc_hmm_migrate_ops, vma, addr, end,
+			  &src_pfn, &dst_pfn, &args);
+	if (ret < 0)
+		ret = H_PARAMETER;
+out:
+	up_read(&kvm->mm->mmap_sem);
+	return ret;
+}
+
+static void
+kvmppc_hmm_fault_migrate_alloc_and_copy(struct vm_area_struct *vma,
+					const unsigned long *src_pfn,
+					unsigned long *dst_pfn,
+					unsigned long start,
+					unsigned long end,
+					void *private)
+{
+	struct page *dpage, *spage;
+	struct kvmppc_hmm_page_pvt *pvt;
+	unsigned long pfn;
+	int ret = U_SUCCESS;
+
+	*dst_pfn = MIGRATE_PFN_ERROR;
+	spage = migrate_pfn_to_page(*src_pfn);
+	if (!spage || !(*src_pfn & MIGRATE_PFN_MIGRATE))
+		return;
+	if (!is_zone_device_page(spage))
+		return;
+	dpage = hmm_vma_alloc_locked_page(vma, start);
+	if (!dpage)
+		return;
+	pvt = (struct kvmppc_hmm_page_pvt *)
+	       hmm_devmem_page_get_drvdata(spage);
+
+	pfn = page_to_pfn(dpage);
+	ret = uv_page_out(pvt->lpid, pfn << PAGE_SHIFT,
+			  pvt->gpa, 0, PAGE_SHIFT);
+	if (ret == U_SUCCESS)
+		*dst_pfn = migrate_pfn(pfn) | MIGRATE_PFN_LOCKED;
+}
+
+/*
+ * This migrate_vma() callback is typically used to updated device
+ * page tables after successful migration. We have nothing to do here.
+ */
+static void
+kvmppc_hmm_fault_migrate_finalize_and_map(struct vm_area_struct *vma,
+					  const unsigned long *src_pfn,
+					  const unsigned long *dst_pfn,
+					  unsigned long start,
+					  unsigned long end,
+					  void *private)
+{
+}
+
+static const struct migrate_vma_ops kvmppc_hmm_fault_migrate_ops = {
+	.alloc_and_copy = kvmppc_hmm_fault_migrate_alloc_and_copy,
+	.finalize_and_map = kvmppc_hmm_fault_migrate_finalize_and_map,
+};
+
+/*
+ * Fault handler callback when HV touches any page that has been
+ * moved to secure memory, we ask UV to give back the page by
+ * issuing a UV_PAGE_OUT uvcall.
+ */
+static vm_fault_t kvmppc_hmm_devmem_fault(struct hmm_devmem *devmem,
+					  struct vm_area_struct *vma,
+					  unsigned long addr,
+					  const struct page *page,
+					  unsigned int flags,
+					  pmd_t *pmdp)
+{
+	unsigned long end = addr + PAGE_SIZE;
+	unsigned long src_pfn, dst_pfn = 0;
+
+	if (migrate_vma(&kvmppc_hmm_fault_migrate_ops, vma, addr, end,
+			&src_pfn, &dst_pfn, NULL))
+		return VM_FAULT_SIGBUS;
+	if (dst_pfn == MIGRATE_PFN_ERROR)
+		return VM_FAULT_SIGBUS;
+	return 0;
+}
+
+static void kvmppc_hmm_devmem_free(struct hmm_devmem *devmem,
+				   struct page *page)
+{
+	kvmppc_hmm_put_page(page);
+}
+
+static const struct hmm_devmem_ops kvmppc_hmm_devmem_ops = {
+	.free = kvmppc_hmm_devmem_free,
+	.fault = kvmppc_hmm_devmem_fault,
+};
+
+/*
+ * Move page from secure memory to normal memory.
+ */
+unsigned long
+kvmppc_h_svm_page_out(struct kvm *kvm, unsigned long gpa,
+		      unsigned long flags, unsigned long page_shift)
+{
+	unsigned long addr, end;
+	struct vm_area_struct *vma;
+	unsigned long src_pfn, dst_pfn = 0;
+	int srcu_idx;
+	int ret = H_SUCCESS;
+
+	if (page_shift != PAGE_SHIFT)
+		return H_P3;
+
+	if (flags)
+		return H_P2;
+
+	srcu_idx = srcu_read_lock(&kvm->srcu);
+	addr = gfn_to_hva(kvm, gpa >> page_shift);
+	srcu_read_unlock(&kvm->srcu, srcu_idx);
+	if (kvm_is_error_hva(addr))
+		return H_PARAMETER;
+
+	end = addr + (1UL << page_shift);
+
+	down_read(&kvm->mm->mmap_sem);
+	vma = find_vma_intersection(kvm->mm, addr, end);
+	if (!vma || vma->vm_start > addr || vma->vm_end < end) {
+		ret = H_PARAMETER;
+		goto out;
+	}
+	ret = migrate_vma(&kvmppc_hmm_fault_migrate_ops, vma, addr, end,
+			  &src_pfn, &dst_pfn, NULL);
+	if (ret < 0)
+		ret = H_PARAMETER;
+out:
+	up_read(&kvm->mm->mmap_sem);
+	return ret;
+}
+
+static u64 kvmppc_get_secmem_size(void)
+{
+	struct device_node *np;
+	int i, len;
+	const __be32 *prop;
+	u64 size = 0;
+
+	np = of_find_node_by_path("/ibm,ultravisor/ibm,uv-firmware");
+	if (!np)
+		goto out;
+
+	prop = of_get_property(np, "secure-memory-ranges", &len);
+	if (!prop)
+		goto out_put;
+
+	for (i = 0; i < len / (sizeof(*prop) * 4); i++)
+		size += of_read_number(prop + (i * 4) + 2, 2);
+
+out_put:
+	of_node_put(np);
+out:
+	return size;
+}
+
+static int kvmppc_hmm_pages_init(void)
+{
+	unsigned long nr_pfns = kvmppc_hmm.devmem->pfn_last -
+				kvmppc_hmm.devmem->pfn_first;
+
+	kvmppc_hmm.pfn_bitmap = kcalloc(BITS_TO_LONGS(nr_pfns),
+					 sizeof(unsigned long), GFP_KERNEL);
+	if (!kvmppc_hmm.pfn_bitmap)
+		return -ENOMEM;
+
+	spin_lock_init(&kvmppc_hmm_lock);
+
+	return 0;
+}
+
+int kvmppc_hmm_init(void)
+{
+	int ret = 0;
+	unsigned long size;
+
+	size = kvmppc_get_secmem_size();
+	if (!size) {
+		ret = -ENODEV;
+		goto out;
+	}
+
+	kvmppc_hmm.device = hmm_device_new(NULL);
+	if (IS_ERR(kvmppc_hmm.device)) {
+		ret = PTR_ERR(kvmppc_hmm.device);
+		goto out;
+	}
+
+	kvmppc_hmm.devmem = hmm_devmem_add(&kvmppc_hmm_devmem_ops,
+					   &kvmppc_hmm.device->device, size);
+	if (IS_ERR(kvmppc_hmm.devmem)) {
+		ret = PTR_ERR(kvmppc_hmm.devmem);
+		goto out_device;
+	}
+	ret = kvmppc_hmm_pages_init();
+	if (ret < 0)
+		goto out_device;
+
+	pr_info("KVMPPC-HMM: Secure Memory size %lx\n", size);
+	return ret;
+
+out_device:
+	hmm_device_put(kvmppc_hmm.device);
+out:
+	return ret;
+}
+
+void kvmppc_hmm_free(void)
+{
+	kfree(kvmppc_hmm.pfn_bitmap);
+	hmm_device_put(kvmppc_hmm.device);
+}