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From: Quentin Perret <qperret@google.com>
To: maz@kernel.org, james.morse@arm.com, alexandru.elisei@arm.com,
	suzuki.poulose@arm.com, catalin.marinas@arm.com, will@kernel.org
Cc: linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org,
	ardb@kernel.org, qwandor@google.com, tabba@google.com,
	dbrazdil@google.com, kernel-team@android.com, qperret@google.com
Subject: [PATCH v4 10/21] KVM: arm64: Enable forcing page-level stage-2 mappings
Date: Mon,  9 Aug 2021 16:24:37 +0100	[thread overview]
Message-ID: <20210809152448.1810400-11-qperret@google.com> (raw)
In-Reply-To: <20210809152448.1810400-1-qperret@google.com>

Much of the stage-2 manipulation logic relies on being able to destroy
block mappings if e.g. installing a smaller mapping in the range. The
rationale for this behaviour is that stage-2 mappings can always be
re-created lazily. However, this gets more complicated when the stage-2
page-table is used to store metadata about the underlying pages. In such
cases, destroying a block mapping may lead to losing part of the state,
and confuse the user of those metadata (such as the hypervisor in nVHE
protected mode).

To avoid this, introduce a callback function in the pgtable struct which
is called during all map operations to determine whether the mappings
can use blocks, or should be forced to page granularity. This is used by
the hypervisor when creating the host stage-2 to force page-level
mappings when using non-default protection attributes.

Signed-off-by: Quentin Perret <qperret@google.com>
---
 arch/arm64/include/asm/kvm_pgtable.h  | 66 +++++++++++++++++----------
 arch/arm64/kvm/hyp/nvhe/mem_protect.c | 34 ++++++++++++--
 arch/arm64/kvm/hyp/pgtable.c          | 29 ++++++++++--
 3 files changed, 94 insertions(+), 35 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 83c5c97d9eac..2c090b0eee77 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -115,25 +115,6 @@ enum kvm_pgtable_stage2_flags {
 	KVM_PGTABLE_S2_IDMAP			= BIT(1),
 };
 
-/**
- * struct kvm_pgtable - KVM page-table.
- * @ia_bits:		Maximum input address size, in bits.
- * @start_level:	Level at which the page-table walk starts.
- * @pgd:		Pointer to the first top-level entry of the page-table.
- * @mm_ops:		Memory management callbacks.
- * @mmu:		Stage-2 KVM MMU struct. Unused for stage-1 page-tables.
- */
-struct kvm_pgtable {
-	u32					ia_bits;
-	u32					start_level;
-	kvm_pte_t				*pgd;
-	struct kvm_pgtable_mm_ops		*mm_ops;
-
-	/* Stage-2 only */
-	struct kvm_s2_mmu			*mmu;
-	enum kvm_pgtable_stage2_flags		flags;
-};
-
 /**
  * enum kvm_pgtable_prot - Page-table permissions and attributes.
  * @KVM_PGTABLE_PROT_X:		Execute permission.
@@ -149,11 +130,43 @@ enum kvm_pgtable_prot {
 	KVM_PGTABLE_PROT_DEVICE			= BIT(3),
 };
 
-#define PAGE_HYP		(KVM_PGTABLE_PROT_R | KVM_PGTABLE_PROT_W)
+#define KVM_PGTABLE_PROT_RW	(KVM_PGTABLE_PROT_R | KVM_PGTABLE_PROT_W)
+#define KVM_PGTABLE_PROT_RWX	(KVM_PGTABLE_PROT_RW | KVM_PGTABLE_PROT_X)
+
+#define PKVM_HOST_MEM_PROT	KVM_PGTABLE_PROT_RWX
+#define PKVM_HOST_MMIO_PROT	KVM_PGTABLE_PROT_RW
+
+#define PAGE_HYP		KVM_PGTABLE_PROT_RW
 #define PAGE_HYP_EXEC		(KVM_PGTABLE_PROT_R | KVM_PGTABLE_PROT_X)
 #define PAGE_HYP_RO		(KVM_PGTABLE_PROT_R)
 #define PAGE_HYP_DEVICE		(PAGE_HYP | KVM_PGTABLE_PROT_DEVICE)
 
+typedef bool (*kvm_pgtable_force_pte_cb_t)(u64 addr, u64 end,
+					   enum kvm_pgtable_prot prot);
+
+/**
+ * struct kvm_pgtable - KVM page-table.
+ * @ia_bits:		Maximum input address size, in bits.
+ * @start_level:	Level at which the page-table walk starts.
+ * @pgd:		Pointer to the first top-level entry of the page-table.
+ * @mm_ops:		Memory management callbacks.
+ * @mmu:		Stage-2 KVM MMU struct. Unused for stage-1 page-tables.
+ * @flags:		Stage-2 page-table flags.
+ * @force_pte_cb:	Function that returns true if page level mappings must
+ *			be used instead of block mappings.
+ */
+struct kvm_pgtable {
+	u32					ia_bits;
+	u32					start_level;
+	kvm_pte_t				*pgd;
+	struct kvm_pgtable_mm_ops		*mm_ops;
+
+	/* Stage-2 only */
+	struct kvm_s2_mmu			*mmu;
+	enum kvm_pgtable_stage2_flags		flags;
+	kvm_pgtable_force_pte_cb_t		force_pte_cb;
+};
+
 /**
  * enum kvm_pgtable_walk_flags - Flags to control a depth-first page-table walk.
  * @KVM_PGTABLE_WALK_LEAF:		Visit leaf entries, including invalid
@@ -246,21 +259,24 @@ int kvm_pgtable_hyp_map(struct kvm_pgtable *pgt, u64 addr, u64 size, u64 phys,
 u64 kvm_get_vtcr(u64 mmfr0, u64 mmfr1, u32 phys_shift);
 
 /**
- * kvm_pgtable_stage2_init_flags() - Initialise a guest stage-2 page-table.
+ * __kvm_pgtable_stage2_init() - Initialise a guest stage-2 page-table.
  * @pgt:	Uninitialised page-table structure to initialise.
  * @arch:	Arch-specific KVM structure representing the guest virtual
  *		machine.
  * @mm_ops:	Memory management callbacks.
  * @flags:	Stage-2 configuration flags.
+ * @force_pte_cb: Function that returns true if page level mappings must
+ *		be used instead of block mappings.
  *
  * Return: 0 on success, negative error code on failure.
  */
-int kvm_pgtable_stage2_init_flags(struct kvm_pgtable *pgt, struct kvm_arch *arch,
-				  struct kvm_pgtable_mm_ops *mm_ops,
-				  enum kvm_pgtable_stage2_flags flags);
+int __kvm_pgtable_stage2_init(struct kvm_pgtable *pgt, struct kvm_arch *arch,
+			      struct kvm_pgtable_mm_ops *mm_ops,
+			      enum kvm_pgtable_stage2_flags flags,
+			      kvm_pgtable_force_pte_cb_t force_pte_cb);
 
 #define kvm_pgtable_stage2_init(pgt, arch, mm_ops) \
-	kvm_pgtable_stage2_init_flags(pgt, arch, mm_ops, 0)
+	__kvm_pgtable_stage2_init(pgt, arch, mm_ops, 0, NULL)
 
 /**
  * kvm_pgtable_stage2_destroy() - Destroy an unused guest stage-2 page-table.
diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index 2148d3968aa5..6fed6772c673 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -89,6 +89,8 @@ static void prepare_host_vtcr(void)
 					  id_aa64mmfr1_el1_sys_val, phys_shift);
 }
 
+static bool host_stage2_force_pte_cb(u64 addr, u64 end, enum kvm_pgtable_prot prot);
+
 int kvm_host_prepare_stage2(void *pgt_pool_base)
 {
 	struct kvm_s2_mmu *mmu = &host_kvm.arch.mmu;
@@ -101,8 +103,9 @@ int kvm_host_prepare_stage2(void *pgt_pool_base)
 	if (ret)
 		return ret;
 
-	ret = kvm_pgtable_stage2_init_flags(&host_kvm.pgt, &host_kvm.arch,
-					    &host_kvm.mm_ops, KVM_HOST_S2_FLAGS);
+	ret = __kvm_pgtable_stage2_init(&host_kvm.pgt, &host_kvm.arch,
+					&host_kvm.mm_ops, KVM_HOST_S2_FLAGS,
+					host_stage2_force_pte_cb);
 	if (ret)
 		return ret;
 
@@ -270,15 +273,36 @@ static int host_stage2_adjust_range(u64 addr, struct kvm_mem_range *range)
 	return 0;
 }
 
+static bool host_stage2_force_pte_cb(u64 addr, u64 end, enum kvm_pgtable_prot prot)
+{
+	/*
+	 * Block mappings must be used with care in the host stage-2 as a
+	 * kvm_pgtable_stage2_map() operation targeting a page in the range of
+	 * an existing block will delete the block under the assumption that
+	 * mappings in the rest of the block range can always be rebuilt lazily.
+	 * That assumption is correct for the host stage-2 with RWX mappings
+	 * targeting memory or RW mappings targeting MMIO ranges (see
+	 * host_stage2_idmap() below which implements some of the host memory
+	 * abort logic). However, this is not safe for any other mappings where
+	 * the host stage-2 page-table is in fact the only place where this
+	 * state is stored. In all those cases, it is safer to use page-level
+	 * mappings, hence avoiding to lose the state because of side-effects in
+	 * kvm_pgtable_stage2_map().
+	 */
+	if (range_is_memory(addr, end))
+		return prot != PKVM_HOST_MEM_PROT;
+	else
+		return prot != PKVM_HOST_MMIO_PROT;
+}
+
 static int host_stage2_idmap(u64 addr)
 {
-	enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_R | KVM_PGTABLE_PROT_W;
 	struct kvm_mem_range range;
 	bool is_memory = find_mem_range(addr, &range);
+	enum kvm_pgtable_prot prot;
 	int ret;
 
-	if (is_memory)
-		prot |= KVM_PGTABLE_PROT_X;
+	prot = is_memory ? PKVM_HOST_MEM_PROT : PKVM_HOST_MMIO_PROT;
 
 	hyp_spin_lock(&host_kvm.lock);
 	ret = host_stage2_adjust_range(addr, &range);
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 2689fcb7901d..e25d829587b9 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -452,6 +452,8 @@ int kvm_pgtable_hyp_init(struct kvm_pgtable *pgt, u32 va_bits,
 	pgt->start_level	= KVM_PGTABLE_MAX_LEVELS - levels;
 	pgt->mm_ops		= mm_ops;
 	pgt->mmu		= NULL;
+	pgt->force_pte_cb	= NULL;
+
 	return 0;
 }
 
@@ -489,6 +491,9 @@ struct stage2_map_data {
 	void				*memcache;
 
 	struct kvm_pgtable_mm_ops	*mm_ops;
+
+	/* Force mappings to page granularity */
+	bool				force_pte;
 };
 
 u64 kvm_get_vtcr(u64 mmfr0, u64 mmfr1, u32 phys_shift)
@@ -602,6 +607,15 @@ static bool stage2_pte_executable(kvm_pte_t pte)
 	return !(pte & KVM_PTE_LEAF_ATTR_HI_S2_XN);
 }
 
+static bool stage2_leaf_mapping_allowed(u64 addr, u64 end, u32 level,
+					struct stage2_map_data *data)
+{
+	if (data->force_pte && (level < (KVM_PGTABLE_MAX_LEVELS - 1)))
+		return false;
+
+	return kvm_block_mapping_supported(addr, end, data->phys, level);
+}
+
 static int stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level,
 				      kvm_pte_t *ptep,
 				      struct stage2_map_data *data)
@@ -611,7 +625,7 @@ static int stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level,
 	struct kvm_pgtable *pgt = data->mmu->pgt;
 	struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops;
 
-	if (!kvm_block_mapping_supported(addr, end, phys, level))
+	if (!stage2_leaf_mapping_allowed(addr, end, level, data))
 		return -E2BIG;
 
 	if (kvm_phys_is_valid(phys))
@@ -655,7 +669,7 @@ static int stage2_map_walk_table_pre(u64 addr, u64 end, u32 level,
 	if (data->anchor)
 		return 0;
 
-	if (!kvm_block_mapping_supported(addr, end, data->phys, level))
+	if (!stage2_leaf_mapping_allowed(addr, end, level, data))
 		return 0;
 
 	data->childp = kvm_pte_follow(*ptep, data->mm_ops);
@@ -785,6 +799,7 @@ int kvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size,
 		.mmu		= pgt->mmu,
 		.memcache	= mc,
 		.mm_ops		= pgt->mm_ops,
+		.force_pte	= pgt->force_pte_cb && pgt->force_pte_cb(addr, addr + size, prot),
 	};
 	struct kvm_pgtable_walker walker = {
 		.cb		= stage2_map_walker,
@@ -816,6 +831,7 @@ int kvm_pgtable_stage2_set_owner(struct kvm_pgtable *pgt, u64 addr, u64 size,
 		.memcache	= mc,
 		.mm_ops		= pgt->mm_ops,
 		.owner_id	= owner_id,
+		.force_pte	= true,
 	};
 	struct kvm_pgtable_walker walker = {
 		.cb		= stage2_map_walker,
@@ -1057,9 +1073,11 @@ int kvm_pgtable_stage2_flush(struct kvm_pgtable *pgt, u64 addr, u64 size)
 	return kvm_pgtable_walk(pgt, addr, size, &walker);
 }
 
-int kvm_pgtable_stage2_init_flags(struct kvm_pgtable *pgt, struct kvm_arch *arch,
-				  struct kvm_pgtable_mm_ops *mm_ops,
-				  enum kvm_pgtable_stage2_flags flags)
+
+int __kvm_pgtable_stage2_init(struct kvm_pgtable *pgt, struct kvm_arch *arch,
+			      struct kvm_pgtable_mm_ops *mm_ops,
+			      enum kvm_pgtable_stage2_flags flags,
+			      kvm_pgtable_force_pte_cb_t force_pte_cb)
 {
 	size_t pgd_sz;
 	u64 vtcr = arch->vtcr;
@@ -1077,6 +1095,7 @@ int kvm_pgtable_stage2_init_flags(struct kvm_pgtable *pgt, struct kvm_arch *arch
 	pgt->mm_ops		= mm_ops;
 	pgt->mmu		= &arch->mmu;
 	pgt->flags		= flags;
+	pgt->force_pte_cb	= force_pte_cb;
 
 	/* Ensure zeroed PGD pages are visible to the hardware walker */
 	dsb(ishst);
-- 
2.32.0.605.g8dce9f2422-goog


  parent reply	other threads:[~2021-08-09 15:25 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-09 15:24 [PATCH v4 00/21] Track shared pages at EL2 in protected mode Quentin Perret
2021-08-09 15:24 ` [PATCH v4 01/21] KVM: arm64: Add hyp_spin_is_locked() for basic locking assertions at EL2 Quentin Perret
2021-08-09 15:24 ` [PATCH v4 02/21] KVM: arm64: Introduce hyp_assert_lock_held() Quentin Perret
2021-08-09 15:24 ` [PATCH v4 03/21] KVM: arm64: Provide the host_stage2_try() helper macro Quentin Perret
2021-08-09 15:24 ` [PATCH v4 04/21] KVM: arm64: Introduce helper to retrieve a PTE and its level Quentin Perret
2021-08-17 13:53   ` Andrew Walbran
2021-08-09 15:24 ` [PATCH v4 05/21] KVM: arm64: Expose page-table helpers Quentin Perret
2021-08-10  4:56   ` Fuad Tabba
2021-08-09 15:24 ` [PATCH v4 06/21] KVM: arm64: Optimize host memory aborts Quentin Perret
2021-08-09 15:24 ` [PATCH v4 07/21] KVM: arm64: Rename KVM_PTE_LEAF_ATTR_S2_IGNORED Quentin Perret
2021-08-09 15:24 ` [PATCH v4 08/21] KVM: arm64: Don't overwrite software bits with owner id Quentin Perret
2021-08-09 15:24 ` [PATCH v4 09/21] KVM: arm64: Tolerate re-creating hyp mappings to set software bits Quentin Perret
2021-08-09 15:24 ` Quentin Perret [this message]
2021-08-10  4:33   ` [PATCH v4 10/21] KVM: arm64: Enable forcing page-level stage-2 mappings Fuad Tabba
2021-08-09 15:24 ` [PATCH v4 11/21] KVM: arm64: Allow populating software bits Quentin Perret
2021-08-10  4:56   ` Fuad Tabba
2021-08-09 15:24 ` [PATCH v4 12/21] KVM: arm64: Add helpers to tag shared pages in SW bits Quentin Perret
2021-08-09 15:24 ` [PATCH v4 13/21] KVM: arm64: Expose host stage-2 manipulation helpers Quentin Perret
2021-08-10  4:36   ` Fuad Tabba
2021-08-09 15:24 ` [PATCH v4 14/21] KVM: arm64: Expose pkvm_hyp_id Quentin Perret
2021-08-10  4:57   ` Fuad Tabba
2021-08-09 15:24 ` [PATCH v4 15/21] KVM: arm64: Introduce addr_is_memory() Quentin Perret
2021-08-10  4:37   ` Fuad Tabba
2021-08-09 15:24 ` [PATCH v4 16/21] KVM: arm64: Enable retrieving protections attributes of PTEs Quentin Perret
2021-08-10  4:38   ` Fuad Tabba
2021-08-09 15:24 ` [PATCH v4 17/21] KVM: arm64: Mark host bss and rodata section as shared Quentin Perret
2021-08-10  4:40   ` Fuad Tabba
2021-08-09 15:24 ` [PATCH v4 18/21] KVM: arm64: Remove __pkvm_mark_hyp Quentin Perret
2021-08-10  4:55   ` Fuad Tabba
2021-08-09 15:24 ` [PATCH v4 19/21] KVM: arm64: Refactor protected nVHE stage-1 locking Quentin Perret
2021-08-10  4:41   ` Fuad Tabba
2021-08-09 15:24 ` [PATCH v4 20/21] KVM: arm64: Restrict EL2 stage-1 changes in protected mode Quentin Perret
2021-08-10  4:43   ` Fuad Tabba
2021-08-09 15:24 ` [PATCH v4 21/21] KVM: arm64: Make __pkvm_create_mappings static Quentin Perret
2021-08-10  4:55   ` Fuad Tabba
2021-08-11 11:25 ` [PATCH v4 00/21] Track shared pages at EL2 in protected mode Marc Zyngier

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