book3s_hv_uvmem.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Secure pages management: Migration of pages between normal and secure
 * memory of KVM guests.
 *
 * Copyright 2018 Bharata B Rao, IBM Corp. <bharata@linux.ibm.com>
 */

/*
 * A pseries guest can be run as 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).
 *
 * The page-in or page-out requests from UV will come to HV as hcalls and
 * HV will call back into UV via ultracalls to satisfy these page requests.
 *
 * Private ZONE_DEVICE memory equal to the amount of secure memory
 * available in the platform for running secure guests is hotplugged.
 * Whenever a page belonging to the guest becomes secure, a page from this
 * private device memory is used to represent and track that secure page
 * on the HV side.
 */

/*
 * Notes on locking
 *
 * kvm->arch.uvmem_lock is a per-guest lock that prevents concurrent
 * page-in and page-out requests for the same GPA. Concurrent accesses
 * can either come via UV (guest vCPUs requesting for same page)
 * or when HV and guest simultaneously access the same page.
 * This mutex serializes the migration of page from HV(normal) to
 * UV(secure) and vice versa. So the serialization points are around
 * migrate_vma routines and page-in/out routines.
 *
 * Per-guest mutex comes with a cost though. Mainly it serializes the
 * fault path as page-out can occur when HV faults on accessing secure
 * guest pages. Currently UV issues page-in requests for all the guest
 * PFNs one at a time during early boot (UV_ESM uvcall), so this is
 * not a cause for concern. Also currently the number of page-outs caused
 * by HV touching secure pages is very very low. If an when UV supports
 * overcommitting, then we might see concurrent guest driven page-outs.
 *
 * Locking order
 *
 * 1. kvm->srcu - Protects KVM memslots
 * 2. kvm->mm->mmap_sem - find_vma, migrate_vma_pages and helpers, ksm_madvise
 * 3. kvm->arch.uvmem_lock - protects read/writes to uvmem slots thus acting
 *			     as sync-points for page-in/out
 */

/*
 * Notes on page size
 *
 * Currently UV uses 2MB mappings internally, but will issue H_SVM_PAGE_IN
 * and H_SVM_PAGE_OUT hcalls in PAGE_SIZE(64K) granularity. HV tracks
 * secure GPAs at 64K page size and maintains one device PFN for each
 * 64K secure GPA. UV_PAGE_IN and UV_PAGE_OUT calls by HV are also issued
 * for 64K page at a time.
 *
 * HV faulting on secure pages: When HV touches any secure page, it
 * faults and issues a UV_PAGE_OUT request with 64K page size. Currently
 * UV splits and remaps the 2MB page if necessary and copies out the
 * required 64K page contents.
 *
 * In summary, the current secure pages handling code in HV assumes
 * 64K page size and in fact fails any page-in/page-out requests of
 * non-64K size upfront. If and when UV starts supporting multiple
 * page-sizes, we need to break this assumption.
 */

#include <linux/pagemap.h>
#include <linux/migrate.h>
#include <linux/kvm_host.h>
#include <linux/ksm.h>
#include <asm/ultravisor.h>
#include <asm/mman.h>
#include <asm/kvm_ppc.h>

static struct dev_pagemap kvmppc_uvmem_pgmap;
static unsigned long *kvmppc_uvmem_bitmap;
static DEFINE_SPINLOCK(kvmppc_uvmem_bitmap_lock);

#define KVMPPC_UVMEM_PFN	(1UL << 63)

struct kvmppc_uvmem_slot {
	struct list_head list;
	unsigned long nr_pfns;
	unsigned long base_pfn;
	unsigned long *pfns;
};

struct kvmppc_uvmem_page_pvt {
	struct kvm *kvm;
	unsigned long gpa;
};

int kvmppc_uvmem_slot_init(struct kvm *kvm, const struct kvm_memory_slot *slot)
{
	struct kvmppc_uvmem_slot *p;

	p = kzalloc(sizeof(*p), GFP_KERNEL);
	if (!p)
		return -ENOMEM;
	p->pfns = vzalloc(array_size(slot->npages, sizeof(*p->pfns)));
	if (!p->pfns) {
		kfree(p);
		return -ENOMEM;
	}
	p->nr_pfns = slot->npages;
	p->base_pfn = slot->base_gfn;

	mutex_lock(&kvm->arch.uvmem_lock);
	list_add(&p->list, &kvm->arch.uvmem_pfns);
	mutex_unlock(&kvm->arch.uvmem_lock);

	return 0;
}

/*
 * All device PFNs are already released by the time we come here.
 */
void kvmppc_uvmem_slot_free(struct kvm *kvm, const struct kvm_memory_slot *slot)
{
	struct kvmppc_uvmem_slot *p, *next;

	mutex_lock(&kvm->arch.uvmem_lock);
	list_for_each_entry_safe(p, next, &kvm->arch.uvmem_pfns, list) {
		if (p->base_pfn == slot->base_gfn) {
			vfree(p->pfns);
			list_del(&p->list);
			kfree(p);
			break;
		}
	}
	mutex_unlock(&kvm->arch.uvmem_lock);
}

static void kvmppc_uvmem_pfn_insert(unsigned long gfn, unsigned long uvmem_pfn,
				    struct kvm *kvm)
{
	struct kvmppc_uvmem_slot *p;

	list_for_each_entry(p, &kvm->arch.uvmem_pfns, list) {
		if (gfn >= p->base_pfn && gfn < p->base_pfn + p->nr_pfns) {
			unsigned long index = gfn - p->base_pfn;

			p->pfns[index] = uvmem_pfn | KVMPPC_UVMEM_PFN;
			return;
		}
	}
}

static void kvmppc_uvmem_pfn_remove(unsigned long gfn, struct kvm *kvm)
{
	struct kvmppc_uvmem_slot *p;

	list_for_each_entry(p, &kvm->arch.uvmem_pfns, list) {
		if (gfn >= p->base_pfn && gfn < p->base_pfn + p->nr_pfns) {
			p->pfns[gfn - p->base_pfn] = 0;
			return;
		}
	}
}

static bool kvmppc_gfn_is_uvmem_pfn(unsigned long gfn, struct kvm *kvm,
				    unsigned long *uvmem_pfn)
{
	struct kvmppc_uvmem_slot *p;

	list_for_each_entry(p, &kvm->arch.uvmem_pfns, list) {
		if (gfn >= p->base_pfn && gfn < p->base_pfn + p->nr_pfns) {
			unsigned long index = gfn - p->base_pfn;

			if (p->pfns[index] & KVMPPC_UVMEM_PFN) {
				if (uvmem_pfn)
					*uvmem_pfn = p->pfns[index] &
						     ~KVMPPC_UVMEM_PFN;
				return true;
			} else
				return false;
		}
	}
	return false;
}

unsigned long kvmppc_h_svm_init_start(struct kvm *kvm)
{
	struct kvm_memslots *slots;
	struct kvm_memory_slot *memslot;
	int ret = H_SUCCESS;
	int srcu_idx;

	if (!kvmppc_uvmem_bitmap)
		return H_UNSUPPORTED;

	/* Only radix guests can be secure guests */
	if (!kvm_is_radix(kvm))
		return H_UNSUPPORTED;

	srcu_idx = srcu_read_lock(&kvm->srcu);
	slots = kvm_memslots(kvm);
	kvm_for_each_memslot(memslot, slots) {
		if (kvmppc_uvmem_slot_init(kvm, memslot)) {
			ret = H_PARAMETER;
			goto out;
		}
		ret = uv_register_mem_slot(kvm->arch.lpid,
					   memslot->base_gfn << PAGE_SHIFT,
					   memslot->npages * PAGE_SIZE,
					   0, memslot->id);
		if (ret < 0) {
			kvmppc_uvmem_slot_free(kvm, memslot);
			ret = H_PARAMETER;
			goto out;
		}
	}
	kvm->arch.secure_guest |= KVMPPC_SECURE_INIT_START;
out:
	srcu_read_unlock(&kvm->srcu, srcu_idx);
	return ret;
}

unsigned long kvmppc_h_svm_init_done(struct kvm *kvm)
{
	if (!(kvm->arch.secure_guest & KVMPPC_SECURE_INIT_START))
		return H_UNSUPPORTED;

	kvm->arch.secure_guest |= KVMPPC_SECURE_INIT_DONE;
	pr_info("LPID %d went secure\n", kvm->arch.lpid);
	return H_SUCCESS;
}

/*
 * Get a free device PFN from the pool
 *
 * Called when a normal page is moved to secure memory (UV_PAGE_IN). Device
 * PFN will be used to keep track of the secure page on HV side.
 *
 * Called with kvm->arch.uvmem_lock held
 */
static struct page *kvmppc_uvmem_get_page(unsigned long gpa, struct kvm *kvm)
{
	struct page *dpage = NULL;
	unsigned long bit, uvmem_pfn;
	struct kvmppc_uvmem_page_pvt *pvt;
	unsigned long pfn_last, pfn_first;

	pfn_first = kvmppc_uvmem_pgmap.res.start >> PAGE_SHIFT;
	pfn_last = pfn_first +
		   (resource_size(&kvmppc_uvmem_pgmap.res) >> PAGE_SHIFT);

	spin_lock(&kvmppc_uvmem_bitmap_lock);
	bit = find_first_zero_bit(kvmppc_uvmem_bitmap,
				  pfn_last - pfn_first);
	if (bit >= (pfn_last - pfn_first))
		goto out;
	bitmap_set(kvmppc_uvmem_bitmap, bit, 1);
	spin_unlock(&kvmppc_uvmem_bitmap_lock);

	pvt = kzalloc(sizeof(*pvt), GFP_KERNEL);
	if (!pvt)
		goto out_clear;

	uvmem_pfn = bit + pfn_first;
	kvmppc_uvmem_pfn_insert(gpa >> PAGE_SHIFT, uvmem_pfn, kvm);

	pvt->gpa = gpa;
	pvt->kvm = kvm;

	dpage = pfn_to_page(uvmem_pfn);
	dpage->zone_device_data = pvt;
	get_page(dpage);
	lock_page(dpage);
	return dpage;
out_clear:
	spin_lock(&kvmppc_uvmem_bitmap_lock);
	bitmap_clear(kvmppc_uvmem_bitmap, bit, 1);
out:
	spin_unlock(&kvmppc_uvmem_bitmap_lock);
	return NULL;
}

/*
 * Alloc a PFN from private device memory pool and copy page from normal
 * memory to secure memory using UV_PAGE_IN uvcall.
 */
static int
kvmppc_svm_page_in(struct vm_area_struct *vma, unsigned long start,
		   unsigned long end, unsigned long gpa, struct kvm *kvm,
		   unsigned long page_shift, bool *downgrade)
{
	unsigned long src_pfn, dst_pfn = 0;
	struct migrate_vma mig;
	struct page *spage;
	unsigned long pfn;
	struct page *dpage;
	int ret = 0;

	memset(&mig, 0, sizeof(mig));
	mig.vma = vma;
	mig.start = start;
	mig.end = end;
	mig.src = &src_pfn;
	mig.dst = &dst_pfn;

	/*
	 * We come here with mmap_sem write lock held just for
	 * ksm_madvise(), otherwise we only need read mmap_sem.
	 * Hence downgrade to read lock once ksm_madvise() is done.
	 */
	ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
			  MADV_UNMERGEABLE, &vma->vm_flags);
	downgrade_write(&kvm->mm->mmap_sem);
	*downgrade = true;
	if (ret)
		return ret;

	ret = migrate_vma_setup(&mig);
	if (ret)
		return ret;

	if (!(*mig.src & MIGRATE_PFN_MIGRATE)) {
		ret = -1;
		goto out_finalize;
	}

	dpage = kvmppc_uvmem_get_page(gpa, kvm);
	if (!dpage) {
		ret = -1;
		goto out_finalize;
	}

	pfn = *mig.src >> MIGRATE_PFN_SHIFT;
	spage = migrate_pfn_to_page(*mig.src);
	if (spage)
		uv_page_in(kvm->arch.lpid, pfn << page_shift, gpa, 0,
			   page_shift);

	*mig.dst = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_LOCKED;
	migrate_vma_pages(&mig);
out_finalize:
	migrate_vma_finalize(&mig);
	return ret;
}

/*
 * H_SVM_PAGE_IN: 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)
{
	bool downgrade = false;
	unsigned long start, end;
	struct vm_area_struct *vma;
	int srcu_idx;
	unsigned long gfn = gpa >> page_shift;
	int ret;

	if (!(kvm->arch.secure_guest & KVMPPC_SECURE_INIT_START))
		return H_UNSUPPORTED;

	if (page_shift != PAGE_SHIFT)
		return H_P3;

	if (flags)
		return H_P2;

	ret = H_PARAMETER;
	srcu_idx = srcu_read_lock(&kvm->srcu);
	down_write(&kvm->mm->mmap_sem);

	start = gfn_to_hva(kvm, gfn);
	if (kvm_is_error_hva(start))
		goto out;

	mutex_lock(&kvm->arch.uvmem_lock);
	/* Fail the page-in request of an already paged-in page */
	if (kvmppc_gfn_is_uvmem_pfn(gfn, kvm, NULL))
		goto out_unlock;

	end = start + (1UL << page_shift);
	vma = find_vma_intersection(kvm->mm, start, end);
	if (!vma || vma->vm_start > start || vma->vm_end < end)
		goto out_unlock;

	if (!kvmppc_svm_page_in(vma, start, end, gpa, kvm, page_shift,
				&downgrade))
		ret = H_SUCCESS;
out_unlock:
	mutex_unlock(&kvm->arch.uvmem_lock);
out:
	if (downgrade)
		up_read(&kvm->mm->mmap_sem);
	else
		up_write(&kvm->mm->mmap_sem);
	srcu_read_unlock(&kvm->srcu, srcu_idx);
	return ret;
}

/*
 * Provision a new page on HV side and copy over the contents
 * from secure memory using UV_PAGE_OUT uvcall.
 */
static int
kvmppc_svm_page_out(struct vm_area_struct *vma, unsigned long start,
		    unsigned long end, unsigned long page_shift,
		    struct kvm *kvm, unsigned long gpa)
{
	unsigned long src_pfn, dst_pfn = 0;
	struct migrate_vma mig;
	struct page *dpage, *spage;
	unsigned long pfn;
	int ret = U_SUCCESS;

	memset(&mig, 0, sizeof(mig));
	mig.vma = vma;
	mig.start = start;
	mig.end = end;
	mig.src = &src_pfn;
	mig.dst = &dst_pfn;

	mutex_lock(&kvm->arch.uvmem_lock);
	/* The requested page is already paged-out, nothing to do */
	if (!kvmppc_gfn_is_uvmem_pfn(gpa >> page_shift, kvm, NULL))
		goto out;

	ret = migrate_vma_setup(&mig);
	if (ret)
		return ret;

	spage = migrate_pfn_to_page(*mig.src);
	if (!spage || !(*mig.src & MIGRATE_PFN_MIGRATE))
		goto out_finalize;

	if (!is_zone_device_page(spage))
		goto out_finalize;

	dpage = alloc_page_vma(GFP_HIGHUSER, vma, start);
	if (!dpage) {
		ret = -1;
		goto out_finalize;
	}

	lock_page(dpage);
	pfn = page_to_pfn(dpage);

	ret = uv_page_out(kvm->arch.lpid, pfn << page_shift,
			  gpa, 0, page_shift);
	if (ret == U_SUCCESS)
		*mig.dst = migrate_pfn(pfn) | MIGRATE_PFN_LOCKED;
	else {
		unlock_page(dpage);
		__free_page(dpage);
		goto out_finalize;
	}

	migrate_vma_pages(&mig);
out_finalize:
	migrate_vma_finalize(&mig);
out:
	mutex_unlock(&kvm->arch.uvmem_lock);
	return ret;
}

/*
 * Fault handler callback that gets called when HV touches any page that
 * has been moved to secure memory, we ask UV to give back the page by
 * issuing UV_PAGE_OUT uvcall.
 *
 * This eventually results in dropping of device PFN and the newly
 * provisioned page/PFN gets populated in QEMU page tables.
 */
static vm_fault_t kvmppc_uvmem_migrate_to_ram(struct vm_fault *vmf)
{
	struct kvmppc_uvmem_page_pvt *pvt = vmf->page->zone_device_data;

	if (kvmppc_svm_page_out(vmf->vma, vmf->address,
				vmf->address + PAGE_SIZE, PAGE_SHIFT,
				pvt->kvm, pvt->gpa))
		return VM_FAULT_SIGBUS;
	else
		return 0;
}

/*
 * Release the device PFN back to the pool
 *
 * Gets called when secure page becomes a normal page during H_SVM_PAGE_OUT.
 * Gets called with kvm->arch.uvmem_lock held.
 */
static void kvmppc_uvmem_page_free(struct page *page)
{
	unsigned long pfn = page_to_pfn(page) -
			(kvmppc_uvmem_pgmap.res.start >> PAGE_SHIFT);
	struct kvmppc_uvmem_page_pvt *pvt;

	spin_lock(&kvmppc_uvmem_bitmap_lock);
	bitmap_clear(kvmppc_uvmem_bitmap, pfn, 1);
	spin_unlock(&kvmppc_uvmem_bitmap_lock);

	pvt = page->zone_device_data;
	page->zone_device_data = NULL;
	kvmppc_uvmem_pfn_remove(pvt->gpa >> PAGE_SHIFT, pvt->kvm);
	kfree(pvt);
}

static const struct dev_pagemap_ops kvmppc_uvmem_ops = {
	.page_free = kvmppc_uvmem_page_free,
	.migrate_to_ram	= kvmppc_uvmem_migrate_to_ram,
};

/*
 * H_SVM_PAGE_OUT: 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 gfn = gpa >> page_shift;
	unsigned long start, end;
	struct vm_area_struct *vma;
	int srcu_idx;
	int ret;

	if (!(kvm->arch.secure_guest & KVMPPC_SECURE_INIT_START))
		return H_UNSUPPORTED;

	if (page_shift != PAGE_SHIFT)
		return H_P3;

	if (flags)
		return H_P2;

	ret = H_PARAMETER;
	srcu_idx = srcu_read_lock(&kvm->srcu);
	down_read(&kvm->mm->mmap_sem);
	start = gfn_to_hva(kvm, gfn);
	if (kvm_is_error_hva(start))
		goto out;

	end = start + (1UL << page_shift);
	vma = find_vma_intersection(kvm->mm, start, end);
	if (!vma || vma->vm_start > start || vma->vm_end < end)
		goto out;

	if (!kvmppc_svm_page_out(vma, start, end, page_shift, kvm, gpa))
		ret = H_SUCCESS;
out:
	up_read(&kvm->mm->mmap_sem);
	srcu_read_unlock(&kvm->srcu, srcu_idx);
	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_compatible_node(NULL, NULL, "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;
}

int kvmppc_uvmem_init(void)
{
	int ret = 0;
	unsigned long size;
	struct resource *res;
	void *addr;
	unsigned long pfn_last, pfn_first;

	size = kvmppc_get_secmem_size();
	if (!size) {
		/*
		 * Don't fail the initialization of kvm-hv module if
		 * the platform doesn't export ibm,uv-firmware node.
		 * Let normal guests run on such PEF-disabled platform.
		 */
		pr_info("KVMPPC-UVMEM: No support for secure guests\n");
		goto out;
	}

	res = request_free_mem_region(&iomem_resource, size, "kvmppc_uvmem");
	if (IS_ERR(res)) {
		ret = PTR_ERR(res);
		goto out;
	}

	kvmppc_uvmem_pgmap.type = MEMORY_DEVICE_PRIVATE;
	kvmppc_uvmem_pgmap.res = *res;
	kvmppc_uvmem_pgmap.ops = &kvmppc_uvmem_ops;
	addr = memremap_pages(&kvmppc_uvmem_pgmap, NUMA_NO_NODE);
	if (IS_ERR(addr)) {
		ret = PTR_ERR(addr);
		goto out_free_region;
	}

	pfn_first = res->start >> PAGE_SHIFT;
	pfn_last = pfn_first + (resource_size(res) >> PAGE_SHIFT);
	kvmppc_uvmem_bitmap = kcalloc(BITS_TO_LONGS(pfn_last - pfn_first),
				      sizeof(unsigned long), GFP_KERNEL);
	if (!kvmppc_uvmem_bitmap) {
		ret = -ENOMEM;
		goto out_unmap;
	}

	pr_info("KVMPPC-UVMEM: Secure Memory size 0x%lx\n", size);
	return ret;
out_unmap:
	memunmap_pages(&kvmppc_uvmem_pgmap);
out_free_region:
	release_mem_region(res->start, size);
out:
	return ret;
}

void kvmppc_uvmem_free(void)
{
	memunmap_pages(&kvmppc_uvmem_pgmap);
	release_mem_region(kvmppc_uvmem_pgmap.res.start,
			   resource_size(&kvmppc_uvmem_pgmap.res));
	kfree(kvmppc_uvmem_bitmap);
}