KVM: SEV: Do cache maintenance on the source VM during intra-host migrationgrafted

Manually perform cache maintenance on the source VM during intra-host
migration to ensure no stale data is left in CPU caches after the VM is
destroyed.  Because the source VM is "converted" to a non-SEV VM, KVM's
memory reclaim flows won't trigger cache maintenance, e.g. when all guest
memory is reclaimed in response to detaching from the mmu_notifier.

Note, relying on the destination VM to do cache maintenance isn't an option
as KVM doesn't require identical guest memory configurations, i.e. the
source VM may have access to memory that the destination VM does not.
Enforcing equivalent memory configurations is infeasible, as it would
require a *deep* comparison of memslots, e.g. to verify that not only are
the memslot identical, but what the memslots point at is also identical.

Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration")
Cc: stable@vger.kernel.org
Reported-by: Stefan Teodorescu <fane@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260923163721.1584779-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 311 insertions, 0 deletions

diff --git a/arch/arm64/kvm/ptdump.c b/arch/arm64/kvm/ptdump.c
new file mode 100644
index 000000000..69899797d
--- /dev/null
+++ b/arch/arm64/kvm/ptdump.c
@@ -0,0 +1,311 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Debug helper used to dump the stage-2 pagetables of the system and their
+ * associated permissions.
+ *
+ * Copyright (C) Google, 2024
+ * Author: Sebastian Ene <sebastianene@google.com>
+ */
+#include <linux/debugfs.h>
+#include <linux/kvm_host.h>
+#include <linux/seq_file.h>
+
+#include <asm/cpufeature.h>
+#include <asm/kvm_mmu.h>
+#include <asm/kvm_pgtable.h>
+#include <asm/ptdump.h>
+
+#define MARKERS_LEN		2
+#define KVM_PGTABLE_MAX_LEVELS	(KVM_PGTABLE_LAST_LEVEL + 1)
+#define S2FNAMESZ		sizeof("0x0123456789abcdef-0x0123456789abcdef-s2-disabled")
+
+struct kvm_ptdump_guest_state {
+	struct kvm_s2_mmu	*mmu;
+	struct ptdump_pg_state	parser_state;
+	struct addr_marker	ipa_marker[MARKERS_LEN];
+	struct ptdump_pg_level	level[KVM_PGTABLE_MAX_LEVELS];
+};
+
+static const struct ptdump_prot_bits stage2_pte_bits[] = {
+	{
+		.mask	= PTE_VALID,
+		.val	= PTE_VALID,
+		.set	= " ",
+		.clear	= "F",
+	},
+	{
+		.mask	= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R,
+		.val	= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R,
+		.set	= "R",
+		.clear	= " ",
+	},
+	{
+		.mask	= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W,
+		.val	= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W,
+		.set	= "W",
+		.clear	= " ",
+	},
+	{
+		.mask	= KVM_PTE_LEAF_ATTR_HI_S2_XN,
+		.val	= 0b00UL << __bf_shf(KVM_PTE_LEAF_ATTR_HI_S2_XN),
+		.set	= "px ux ",
+	},
+	{
+		.mask	= KVM_PTE_LEAF_ATTR_HI_S2_XN,
+		.val	= 0b01UL << __bf_shf(KVM_PTE_LEAF_ATTR_HI_S2_XN),
+		.set	= "PXNux ",
+	},
+	{
+		.mask	= KVM_PTE_LEAF_ATTR_HI_S2_XN,
+		.val	= 0b10UL << __bf_shf(KVM_PTE_LEAF_ATTR_HI_S2_XN),
+		.set	= "PXNUXN",
+	},
+	{
+		.mask	= KVM_PTE_LEAF_ATTR_HI_S2_XN,
+		.val	= 0b11UL << __bf_shf(KVM_PTE_LEAF_ATTR_HI_S2_XN),
+		.set	= "px UXN",
+	},
+	{
+		.mask	= KVM_PTE_LEAF_ATTR_LO_S2_AF,
+		.val	= KVM_PTE_LEAF_ATTR_LO_S2_AF,
+		.set	= "AF",
+		.clear	= "  ",
+	},
+	{
+		.mask	= PMD_TYPE_MASK,
+		.val	= PMD_TYPE_SECT,
+		.set	= "BLK",
+		.clear	= "   ",
+	},
+};
+
+static int kvm_ptdump_visitor(const struct kvm_pgtable_visit_ctx *ctx,
+			      enum kvm_pgtable_walk_flags visit)
+{
+	struct ptdump_pg_state *st = ctx->arg;
+	struct ptdump_state *pt_st = &st->ptdump;
+
+	note_page(pt_st, ctx->addr, ctx->level, ctx->old);
+
+	return 0;
+}
+
+static int kvm_ptdump_build_levels(struct ptdump_pg_level *level, u32 start_lvl)
+{
+	u32 i;
+	u64 mask;
+
+	if (WARN_ON_ONCE(start_lvl >= KVM_PGTABLE_LAST_LEVEL))
+		return -EINVAL;
+
+	mask = 0;
+	for (i = 0; i < ARRAY_SIZE(stage2_pte_bits); i++)
+		mask |= stage2_pte_bits[i].mask;
+
+	for (i = start_lvl; i < KVM_PGTABLE_MAX_LEVELS; i++) {
+		snprintf(level[i].name, sizeof(level[i].name), "%u", i);
+
+		level[i].num	= ARRAY_SIZE(stage2_pte_bits);
+		level[i].bits	= stage2_pte_bits;
+		level[i].mask	= mask;
+	}
+
+	return 0;
+}
+
+static struct kvm_ptdump_guest_state *kvm_ptdump_parser_create(struct kvm_s2_mmu *mmu)
+{
+	struct kvm_ptdump_guest_state *st;
+	struct kvm_pgtable *pgtable = mmu->pgt;
+	int ret;
+
+	st = kzalloc_obj(struct kvm_ptdump_guest_state, GFP_KERNEL_ACCOUNT);
+	if (!st)
+		return ERR_PTR(-ENOMEM);
+
+	ret = kvm_ptdump_build_levels(&st->level[0], pgtable->start_level);
+	if (ret) {
+		kfree(st);
+		return ERR_PTR(ret);
+	}
+
+	st->ipa_marker[0].name		= "Guest IPA";
+	st->ipa_marker[1].start_address = ULONG_MAX;
+
+	st->mmu				= mmu;
+	return st;
+}
+
+static int kvm_ptdump_guest_show(struct seq_file *m, void *unused)
+{
+	int ret;
+	struct kvm_ptdump_guest_state *st = m->private;
+	struct kvm_s2_mmu *mmu = st->mmu;
+	struct kvm *kvm = kvm_s2_mmu_to_kvm(mmu);
+	struct kvm_pgtable_walker walker = (struct kvm_pgtable_walker) {
+		.cb	= kvm_ptdump_visitor,
+		.arg	= &st->parser_state,
+		.flags	= KVM_PGTABLE_WALK_LEAF,
+	};
+
+	guard(write_lock)(&kvm->mmu_lock);
+	st->parser_state = (struct ptdump_pg_state) {
+		.marker		= &st->ipa_marker[0],
+		.end_address	= BIT(mmu->pgt->ia_bits),
+		.level		= -1,
+		.pg_level	= &st->level[0],
+		.seq		= m,
+	};
+
+	ret = kvm_pgtable_walk(mmu->pgt, 0, BIT(mmu->pgt->ia_bits), &walker);
+	if (ret)
+		return ret;
+	note_page_flush(&st->parser_state.ptdump);
+
+	return 0;
+}
+
+static int kvm_ptdump_guest_open(struct inode *m, struct file *file)
+{
+	struct kvm_s2_mmu *mmu = m->i_private;
+	struct kvm *kvm = kvm_s2_mmu_to_kvm(mmu);
+	struct kvm_ptdump_guest_state *st;
+	int ret;
+
+	if (!kvm_get_kvm_safe(kvm))
+		return -ENOENT;
+
+	st = kvm_ptdump_parser_create(mmu);
+	if (IS_ERR(st)) {
+		ret = PTR_ERR(st);
+		goto err_with_kvm_ref;
+	}
+
+	ret = single_open(file, kvm_ptdump_guest_show, st);
+	if (!ret)
+		return 0;
+
+	kfree(st);
+err_with_kvm_ref:
+	kvm_put_kvm(kvm);
+	return ret;
+}
+
+static int kvm_ptdump_guest_close(struct inode *m, struct file *file)
+{
+	struct kvm *kvm = kvm_s2_mmu_to_kvm(m->i_private);
+	void *st = ((struct seq_file *)file->private_data)->private;
+
+	kfree(st);
+	kvm_put_kvm(kvm);
+
+	return single_release(m, file);
+}
+
+static const struct file_operations kvm_ptdump_guest_fops = {
+	.open		= kvm_ptdump_guest_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= kvm_ptdump_guest_close,
+};
+
+static int kvm_pgtable_range_show(struct seq_file *m, void *unused)
+{
+	struct kvm_pgtable *pgtable = m->private;
+
+	seq_printf(m, "%2u\n", pgtable->ia_bits);
+	return 0;
+}
+
+static int kvm_pgtable_levels_show(struct seq_file *m, void *unused)
+{
+	struct kvm_pgtable *pgtable = m->private;
+
+	seq_printf(m, "%1d\n", KVM_PGTABLE_MAX_LEVELS - pgtable->start_level);
+	return 0;
+}
+
+static int kvm_pgtable_debugfs_open(struct inode *m, struct file *file,
+				    int (*show)(struct seq_file *, void *))
+{
+	struct kvm_s2_mmu *mmu = m->i_private;
+	struct kvm *kvm = kvm_s2_mmu_to_kvm(mmu);
+	struct kvm_pgtable *pgtable;
+	int ret;
+
+	if (!kvm_get_kvm_safe(kvm))
+		return -ENOENT;
+
+	pgtable = mmu->pgt;
+
+	ret = single_open(file, show, pgtable);
+	if (ret < 0)
+		kvm_put_kvm(kvm);
+	return ret;
+}
+
+static int kvm_pgtable_range_open(struct inode *m, struct file *file)
+{
+	return kvm_pgtable_debugfs_open(m, file, kvm_pgtable_range_show);
+}
+
+static int kvm_pgtable_levels_open(struct inode *m, struct file *file)
+{
+	return kvm_pgtable_debugfs_open(m, file, kvm_pgtable_levels_show);
+}
+
+static int kvm_pgtable_debugfs_close(struct inode *m, struct file *file)
+{
+	struct kvm *kvm = kvm_s2_mmu_to_kvm(m->i_private);
+
+	kvm_put_kvm(kvm);
+	return single_release(m, file);
+}
+
+static const struct file_operations kvm_pgtable_range_fops = {
+	.open		= kvm_pgtable_range_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= kvm_pgtable_debugfs_close,
+};
+
+static const struct file_operations kvm_pgtable_levels_fops = {
+	.open		= kvm_pgtable_levels_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= kvm_pgtable_debugfs_close,
+};
+
+void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu)
+{
+	struct dentry *dent;
+	char file_name[S2FNAMESZ];
+
+	snprintf(file_name, sizeof(file_name), "0x%016llx-0x%016llx-s2-%sabled",
+		 mmu->tlb_vttbr,
+		 mmu->tlb_vtcr,
+		 mmu->nested_stage2_enabled ? "en" : "dis");
+
+	dent = debugfs_create_file(file_name, 0400,
+				   mmu->arch->debugfs_nv_dentry, mmu,
+				   &kvm_ptdump_guest_fops);
+
+	mmu->shadow_pt_debugfs_dentry = dent;
+}
+
+void kvm_nested_s2_ptdump_remove_debugfs(struct kvm_s2_mmu *mmu)
+{
+	debugfs_remove(mmu->shadow_pt_debugfs_dentry);
+}
+
+void kvm_s2_ptdump_create_debugfs(struct kvm *kvm)
+{
+	debugfs_create_file("stage2_page_tables", 0400, kvm->debugfs_dentry,
+			    &kvm->arch.mmu, &kvm_ptdump_guest_fops);
+	debugfs_create_file("ipa_range", 0400, kvm->debugfs_dentry,
+			    &kvm->arch.mmu, &kvm_pgtable_range_fops);
+	debugfs_create_file("stage2_levels", 0400, kvm->debugfs_dentry,
+			    &kvm->arch.mmu, &kvm_pgtable_levels_fops);
+	if (cpus_have_final_cap(ARM64_HAS_NESTED_VIRT))
+		kvm->arch.debugfs_nv_dentry = debugfs_create_dir("nested", kvm->debugfs_dentry);
+}