[PATCH v3 00/15] KVM: arm64: Parallel stage-2 fault handling

[PATCH v3 00/15] KVM: arm64: Parallel stage-2 fault handling

[Oliver Upton]

Presently KVM only takes a read lock for stage 2 faults if it believes
the fault can be fixed by relaxing permissions on a PTE (write unprotect
for dirty logging). Otherwise, stage 2 faults grab the write lock, which
predictably can pile up all the vCPUs in a sufficiently large VM.

Like the TDP MMU for x86, this series loosens the locking around
manipulations of the stage 2 page tables to allow parallel faults. RCU
and atomics are exploited to safely build/destroy the stage 2 page
tables in light of multiple software observers.

Patches 1-4 clean up the context associated with a page table walk / PTE
visit. This is helpful for:
 - Extending the context passed through for a visit
 - Building page table walkers that operate outside of a kvm_pgtable
   context (e.g. RCU callback)

Patches 5-6 clean up the stage-2 map walkers by calling a helper to tear
down removed tables. There is a small improvement here in that a broken
PTE is replaced more quickly, as page table teardown happens afterwards.

Patches 7-9 sprinkle in RCU to the page table walkers, punting the
teardown of removed tables to an RCU callback.

Patches 10-14 implement the meat of this series, extending the
'break-before-make' sequence with atomics to realize locking on PTEs.
Effectively a cmpxchg() is used to 'break' a PTE, thereby serializing
changes to a given PTE.

Finally, patch 15 flips the switch on all the new code and starts
grabbing the read side of the MMU lock for stage 2 faults.

Applies to 6.1-rc2. Tested with KVM selftests, kvm-unit-tests, and
Google's internal VMM (Vanadium). Also tested with lockdep enabled and
saw no puke for RCU.

Branch available at:

  https://github.com/oupton/linux kvm-arm64/parallel_mmu

benchmarked with dirty_log_perf_test, scaling from 1 to 48 vCPUs with
4GB of memory per vCPU backed by THP.

  ./dirty_log_perf_test -s anonymous_thp -m 2 -b 4G -v ${NR_VCPUS}

Time to dirty memory:

        +-------+----------+-------------------+
        | vCPUs | 6.1-rc2  | 6.1-rc2 + series  |
        +-------+----------+-------------------+
        |     1 | 0.87s    | 0.93s             |
        |     2 | 1.11s    | 1.16s             |
        |     4 | 2.39s    | 1.27s             |
        |     8 | 5.01s    | 1.39s             |
        |    16 | 8.89s    | 2.07s             |
        |    32 | 19.90s   | 4.45s             |
        |    48 | 32.10s   | 6.23s             |
        +-------+----------+-------------------+

It is also worth mentioning that the time to populate memory has
improved:

        +-------+----------+-------------------+
        | vCPUs | 6.1-rc2  | 6.1-rc2 + series  |
        +-------+----------+-------------------+
        |     1 | 0.21s    | 0.17s             |
        |     2 | 0.26s    | 0.23s             |
        |     4 | 0.39s    | 0.31s             |
        |     8 | 0.68s    | 0.39s             |
        |    16 | 1.26s    | 0.53s             |
        |    32 | 2.51s    | 1.04s             |
        |    48 | 3.94s    | 1.55s             |
        +-------+----------+-------------------+

v2 -> v3:
 - Drop const qualifier from opaque argument pointer. The whole visitor
   context is passed as a const pointer.
 - kvm_set_spte_gfn() is called under the write lock; don't set the
   SHARED bit in this case (Sean).
 - Fix build warning resulting from reparameterization residue (test
   robot).
 - Add an assertion that the RCU read lock is held before the raw
   pointer is used in visitors (Marc, off list).

v1 -> v2:
 - It builds! :-)
 - Roll all of the context associated with PTE visit into a
   stack-allocated structure
 - Clean up the oddball handling of PTE values, avoiding a UAF along the
   way (Quentin)
 - Leave the re-reading of the PTE after WALK_LEAF in place instead of
   attempting to return the installed PTE value (David)
 - Mention why RCU is stubbed out for hyp page table walkers (David)
 - Ensure that all reads of page table memory pass through an
   RCU-protected pointer. The lifetime of the dereference is contained
   within __kvm_pgtable_visit() (David).
 - Ensure that no user of stage2_map_walker() passes TABLE_POST (David)
 - Unwire the page table walkers from relying on struct kvm_pgtable,
   simplifying the passed context to RCU callbacks.
 - Key rcu_dereference() off of a page table flag indicating a shared
   walk. This is clear when either (1) the write lock is held or (2)
   called from an RCU callback.

v1: https://lore.kernel.org/kvmarm/20220830194132.962932-1-oliver.upton@linux.dev/
v2: https://lore.kernel.org/kvmarm/20221007232818.459650-1-oliver.upton@linux.dev/

Oliver Upton (15):
  KVM: arm64: Combine visitor arguments into a context structure
  KVM: arm64: Stash observed pte value in visitor context
  KVM: arm64: Pass mm_ops through the visitor context
  KVM: arm64: Don't pass kvm_pgtable through kvm_pgtable_walk_data
  KVM: arm64: Add a helper to tear down unlinked stage-2 subtrees
  KVM: arm64: Tear down unlinked stage-2 subtree after break-before-make
  KVM: arm64: Use an opaque type for pteps
  KVM: arm64: Protect stage-2 traversal with RCU
  KVM: arm64: Free removed stage-2 tables in RCU callback
  KVM: arm64: Atomically update stage 2 leaf attributes in parallel
    walks
  KVM: arm64: Split init and set for table PTE
  KVM: arm64: Make block->table PTE changes parallel-aware
  KVM: arm64: Make leaf->leaf PTE changes parallel-aware
  KVM: arm64: Make table->block changes parallel-aware
  KVM: arm64: Handle stage-2 faults in parallel

 arch/arm64/include/asm/kvm_pgtable.h  |  92 +++-
 arch/arm64/kvm/hyp/nvhe/mem_protect.c |  21 +-
 arch/arm64/kvm/hyp/nvhe/setup.c       |  22 +-
 arch/arm64/kvm/hyp/pgtable.c          | 624 ++++++++++++++------------
 arch/arm64/kvm/mmu.c                  |  51 ++-
 5 files changed, 463 insertions(+), 347 deletions(-)


base-commit: 247f34f7b80357943234f93f247a1ae6b6c3a740
-- 
2.38.1.273.g43a17bfeac-goog


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[PATCH v3 01/15] KVM: arm64: Combine visitor arguments into a context structure

[Oliver Upton]

Passing new arguments by value to the visitor callbacks is extremely
inflexible for stuffing new parameters used by only some of the
visitors. Use a context structure instead and pass the pointer through
to the visitor callback.

While at it, redefine the 'flags' parameter to the visitor to contain
the bit indicating the phase of the walk. Pass the entire set of flags
through the context structure such that the walker can communicate
additional state to the visitor callback.

No functional change intended.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/include/asm/kvm_pgtable.h  |  15 +-
 arch/arm64/kvm/hyp/nvhe/mem_protect.c |  10 +-
 arch/arm64/kvm/hyp/nvhe/setup.c       |  16 +-
 arch/arm64/kvm/hyp/pgtable.c          | 269 +++++++++++++-------------
 4 files changed, 154 insertions(+), 156 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 3252eb50ecfe..607f9bb8aab4 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -199,10 +199,17 @@ enum kvm_pgtable_walk_flags {
 	KVM_PGTABLE_WALK_TABLE_POST		= BIT(2),
 };
 
-typedef int (*kvm_pgtable_visitor_fn_t)(u64 addr, u64 end, u32 level,
-					kvm_pte_t *ptep,
-					enum kvm_pgtable_walk_flags flag,
-					void * const arg);
+struct kvm_pgtable_visit_ctx {
+	kvm_pte_t				*ptep;
+	void					*arg;
+	u64					addr;
+	u64					end;
+	u32					level;
+	enum kvm_pgtable_walk_flags		flags;
+};
+
+typedef int (*kvm_pgtable_visitor_fn_t)(const struct kvm_pgtable_visit_ctx *ctx,
+					enum kvm_pgtable_walk_flags visit);
 
 /**
  * struct kvm_pgtable_walker - Hook into a page-table walk.
diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index 1e78acf9662e..8f5b6a36a039 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -417,13 +417,11 @@ struct check_walk_data {
 	enum pkvm_page_state	(*get_page_state)(kvm_pte_t pte);
 };
 
-static int __check_page_state_visitor(u64 addr, u64 end, u32 level,
-				      kvm_pte_t *ptep,
-				      enum kvm_pgtable_walk_flags flag,
-				      void * const arg)
+static int __check_page_state_visitor(const struct kvm_pgtable_visit_ctx *ctx,
+				      enum kvm_pgtable_walk_flags visit)
 {
-	struct check_walk_data *d = arg;
-	kvm_pte_t pte = *ptep;
+	struct check_walk_data *d = ctx->arg;
+	kvm_pte_t pte = *ctx->ptep;
 
 	if (kvm_pte_valid(pte) && !addr_is_memory(kvm_pte_to_phys(pte)))
 		return -EINVAL;
diff --git a/arch/arm64/kvm/hyp/nvhe/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
index e8d4ea2fcfa0..a293cf5eba1b 100644
--- a/arch/arm64/kvm/hyp/nvhe/setup.c
+++ b/arch/arm64/kvm/hyp/nvhe/setup.c
@@ -186,15 +186,13 @@ static void hpool_put_page(void *addr)
 	hyp_put_page(&hpool, addr);
 }
 
-static int finalize_host_mappings_walker(u64 addr, u64 end, u32 level,
-					 kvm_pte_t *ptep,
-					 enum kvm_pgtable_walk_flags flag,
-					 void * const arg)
+static int finalize_host_mappings_walker(const struct kvm_pgtable_visit_ctx *ctx,
+					 enum kvm_pgtable_walk_flags visit)
 {
-	struct kvm_pgtable_mm_ops *mm_ops = arg;
+	struct kvm_pgtable_mm_ops *mm_ops = ctx->arg;
 	enum kvm_pgtable_prot prot;
 	enum pkvm_page_state state;
-	kvm_pte_t pte = *ptep;
+	kvm_pte_t pte = *ctx->ptep;
 	phys_addr_t phys;
 
 	if (!kvm_pte_valid(pte))
@@ -205,11 +203,11 @@ static int finalize_host_mappings_walker(u64 addr, u64 end, u32 level,
 	 * was unable to access the hyp_vmemmap and so the buddy allocator has
 	 * initialised the refcount to '1'.
 	 */
-	mm_ops->get_page(ptep);
-	if (flag != KVM_PGTABLE_WALK_LEAF)
+	mm_ops->get_page(ctx->ptep);
+	if (visit != KVM_PGTABLE_WALK_LEAF)
 		return 0;
 
-	if (level != (KVM_PGTABLE_MAX_LEVELS - 1))
+	if (ctx->level != (KVM_PGTABLE_MAX_LEVELS - 1))
 		return -EINVAL;
 
 	phys = kvm_pte_to_phys(pte);
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index cdf8e76b0be1..900c8b9c0cfc 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -64,20 +64,20 @@ static bool kvm_phys_is_valid(u64 phys)
 	return phys < BIT(id_aa64mmfr0_parange_to_phys_shift(ID_AA64MMFR0_EL1_PARANGE_MAX));
 }
 
-static bool kvm_block_mapping_supported(u64 addr, u64 end, u64 phys, u32 level)
+static bool kvm_block_mapping_supported(const struct kvm_pgtable_visit_ctx *ctx, u64 phys)
 {
-	u64 granule = kvm_granule_size(level);
+	u64 granule = kvm_granule_size(ctx->level);
 
-	if (!kvm_level_supports_block_mapping(level))
+	if (!kvm_level_supports_block_mapping(ctx->level))
 		return false;
 
-	if (granule > (end - addr))
+	if (granule > (ctx->end - ctx->addr))
 		return false;
 
 	if (kvm_phys_is_valid(phys) && !IS_ALIGNED(phys, granule))
 		return false;
 
-	return IS_ALIGNED(addr, granule);
+	return IS_ALIGNED(ctx->addr, granule);
 }
 
 static u32 kvm_pgtable_idx(struct kvm_pgtable_walk_data *data, u32 level)
@@ -172,12 +172,12 @@ static kvm_pte_t kvm_init_invalid_leaf_owner(u8 owner_id)
 	return FIELD_PREP(KVM_INVALID_PTE_OWNER_MASK, owner_id);
 }
 
-static int kvm_pgtable_visitor_cb(struct kvm_pgtable_walk_data *data, u64 addr,
-				  u32 level, kvm_pte_t *ptep,
-				  enum kvm_pgtable_walk_flags flag)
+static int kvm_pgtable_visitor_cb(struct kvm_pgtable_walk_data *data,
+				  const struct kvm_pgtable_visit_ctx *ctx,
+				  enum kvm_pgtable_walk_flags visit)
 {
 	struct kvm_pgtable_walker *walker = data->walker;
-	return walker->cb(addr, data->end, level, ptep, flag, walker->arg);
+	return walker->cb(ctx, visit);
 }
 
 static int __kvm_pgtable_walk(struct kvm_pgtable_walk_data *data,
@@ -186,20 +186,24 @@ static int __kvm_pgtable_walk(struct kvm_pgtable_walk_data *data,
 static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
 				      kvm_pte_t *ptep, u32 level)
 {
+	enum kvm_pgtable_walk_flags flags = data->walker->flags;
+	struct kvm_pgtable_visit_ctx ctx = {
+		.ptep	= ptep,
+		.arg	= data->walker->arg,
+		.addr	= data->addr,
+		.end	= data->end,
+		.level	= level,
+		.flags	= flags,
+	};
 	int ret = 0;
-	u64 addr = data->addr;
 	kvm_pte_t *childp, pte = *ptep;
 	bool table = kvm_pte_table(pte, level);
-	enum kvm_pgtable_walk_flags flags = data->walker->flags;
 
-	if (table && (flags & KVM_PGTABLE_WALK_TABLE_PRE)) {
-		ret = kvm_pgtable_visitor_cb(data, addr, level, ptep,
-					     KVM_PGTABLE_WALK_TABLE_PRE);
-	}
+	if (table && (ctx.flags & KVM_PGTABLE_WALK_TABLE_PRE))
+		ret = kvm_pgtable_visitor_cb(data, &ctx, KVM_PGTABLE_WALK_TABLE_PRE);
 
-	if (!table && (flags & KVM_PGTABLE_WALK_LEAF)) {
-		ret = kvm_pgtable_visitor_cb(data, addr, level, ptep,
-					     KVM_PGTABLE_WALK_LEAF);
+	if (!table && (ctx.flags & KVM_PGTABLE_WALK_LEAF)) {
+		ret = kvm_pgtable_visitor_cb(data, &ctx, KVM_PGTABLE_WALK_LEAF);
 		pte = *ptep;
 		table = kvm_pte_table(pte, level);
 	}
@@ -218,10 +222,8 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
 	if (ret)
 		goto out;
 
-	if (flags & KVM_PGTABLE_WALK_TABLE_POST) {
-		ret = kvm_pgtable_visitor_cb(data, addr, level, ptep,
-					     KVM_PGTABLE_WALK_TABLE_POST);
-	}
+	if (ctx.flags & KVM_PGTABLE_WALK_TABLE_POST)
+		ret = kvm_pgtable_visitor_cb(data, &ctx, KVM_PGTABLE_WALK_TABLE_POST);
 
 out:
 	return ret;
@@ -292,13 +294,13 @@ struct leaf_walk_data {
 	u32		level;
 };
 
-static int leaf_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
-		       enum kvm_pgtable_walk_flags flag, void * const arg)
+static int leaf_walker(const struct kvm_pgtable_visit_ctx *ctx,
+		       enum kvm_pgtable_walk_flags visit)
 {
-	struct leaf_walk_data *data = arg;
+	struct leaf_walk_data *data = ctx->arg;
 
-	data->pte   = *ptep;
-	data->level = level;
+	data->pte   = *ctx->ptep;
+	data->level = ctx->level;
 
 	return 0;
 }
@@ -383,47 +385,47 @@ enum kvm_pgtable_prot kvm_pgtable_hyp_pte_prot(kvm_pte_t pte)
 	return prot;
 }
 
-static bool hyp_map_walker_try_leaf(u64 addr, u64 end, u32 level,
-				    kvm_pte_t *ptep, struct hyp_map_data *data)
+static bool hyp_map_walker_try_leaf(const struct kvm_pgtable_visit_ctx *ctx,
+				    struct hyp_map_data *data)
 {
-	kvm_pte_t new, old = *ptep;
-	u64 granule = kvm_granule_size(level), phys = data->phys;
+	kvm_pte_t new, old = *ctx->ptep;
+	u64 granule = kvm_granule_size(ctx->level), phys = data->phys;
 
-	if (!kvm_block_mapping_supported(addr, end, phys, level))
+	if (!kvm_block_mapping_supported(ctx, phys))
 		return false;
 
 	data->phys += granule;
-	new = kvm_init_valid_leaf_pte(phys, data->attr, level);
+	new = kvm_init_valid_leaf_pte(phys, data->attr, ctx->level);
 	if (old == new)
 		return true;
 	if (!kvm_pte_valid(old))
-		data->mm_ops->get_page(ptep);
+		data->mm_ops->get_page(ctx->ptep);
 	else if (WARN_ON((old ^ new) & ~KVM_PTE_LEAF_ATTR_HI_SW))
 		return false;
 
-	smp_store_release(ptep, new);
+	smp_store_release(ctx->ptep, new);
 	return true;
 }
 
-static int hyp_map_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
-			  enum kvm_pgtable_walk_flags flag, void * const arg)
+static int hyp_map_walker(const struct kvm_pgtable_visit_ctx *ctx,
+			  enum kvm_pgtable_walk_flags visit)
 {
 	kvm_pte_t *childp;
-	struct hyp_map_data *data = arg;
+	struct hyp_map_data *data = ctx->arg;
 	struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops;
 
-	if (hyp_map_walker_try_leaf(addr, end, level, ptep, arg))
+	if (hyp_map_walker_try_leaf(ctx, data))
 		return 0;
 
-	if (WARN_ON(level == KVM_PGTABLE_MAX_LEVELS - 1))
+	if (WARN_ON(ctx->level == KVM_PGTABLE_MAX_LEVELS - 1))
 		return -EINVAL;
 
 	childp = (kvm_pte_t *)mm_ops->zalloc_page(NULL);
 	if (!childp)
 		return -ENOMEM;
 
-	kvm_set_table_pte(ptep, childp, mm_ops);
-	mm_ops->get_page(ptep);
+	kvm_set_table_pte(ctx->ptep, childp, mm_ops);
+	mm_ops->get_page(ctx->ptep);
 	return 0;
 }
 
@@ -456,39 +458,39 @@ struct hyp_unmap_data {
 	struct kvm_pgtable_mm_ops	*mm_ops;
 };
 
-static int hyp_unmap_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
-			    enum kvm_pgtable_walk_flags flag, void * const arg)
+static int hyp_unmap_walker(const struct kvm_pgtable_visit_ctx *ctx,
+			    enum kvm_pgtable_walk_flags visit)
 {
-	kvm_pte_t pte = *ptep, *childp = NULL;
-	u64 granule = kvm_granule_size(level);
-	struct hyp_unmap_data *data = arg;
+	kvm_pte_t pte = *ctx->ptep, *childp = NULL;
+	u64 granule = kvm_granule_size(ctx->level);
+	struct hyp_unmap_data *data = ctx->arg;
 	struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops;
 
 	if (!kvm_pte_valid(pte))
 		return -EINVAL;
 
-	if (kvm_pte_table(pte, level)) {
+	if (kvm_pte_table(pte, ctx->level)) {
 		childp = kvm_pte_follow(pte, mm_ops);
 
 		if (mm_ops->page_count(childp) != 1)
 			return 0;
 
-		kvm_clear_pte(ptep);
+		kvm_clear_pte(ctx->ptep);
 		dsb(ishst);
-		__tlbi_level(vae2is, __TLBI_VADDR(addr, 0), level);
+		__tlbi_level(vae2is, __TLBI_VADDR(ctx->addr, 0), ctx->level);
 	} else {
-		if (end - addr < granule)
+		if (ctx->end - ctx->addr < granule)
 			return -EINVAL;
 
-		kvm_clear_pte(ptep);
+		kvm_clear_pte(ctx->ptep);
 		dsb(ishst);
-		__tlbi_level(vale2is, __TLBI_VADDR(addr, 0), level);
+		__tlbi_level(vale2is, __TLBI_VADDR(ctx->addr, 0), ctx->level);
 		data->unmapped += granule;
 	}
 
 	dsb(ish);
 	isb();
-	mm_ops->put_page(ptep);
+	mm_ops->put_page(ctx->ptep);
 
 	if (childp)
 		mm_ops->put_page(childp);
@@ -532,18 +534,18 @@ int kvm_pgtable_hyp_init(struct kvm_pgtable *pgt, u32 va_bits,
 	return 0;
 }
 
-static int hyp_free_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
-			   enum kvm_pgtable_walk_flags flag, void * const arg)
+static int hyp_free_walker(const struct kvm_pgtable_visit_ctx *ctx,
+			   enum kvm_pgtable_walk_flags visit)
 {
-	struct kvm_pgtable_mm_ops *mm_ops = arg;
-	kvm_pte_t pte = *ptep;
+	struct kvm_pgtable_mm_ops *mm_ops = ctx->arg;
+	kvm_pte_t pte = *ctx->ptep;
 
 	if (!kvm_pte_valid(pte))
 		return 0;
 
-	mm_ops->put_page(ptep);
+	mm_ops->put_page(ctx->ptep);
 
-	if (kvm_pte_table(pte, level))
+	if (kvm_pte_table(pte, ctx->level))
 		mm_ops->put_page(kvm_pte_follow(pte, mm_ops));
 
 	return 0;
@@ -682,19 +684,19 @@ static bool stage2_pte_is_counted(kvm_pte_t pte)
 	return !!pte;
 }
 
-static void stage2_put_pte(kvm_pte_t *ptep, struct kvm_s2_mmu *mmu, u64 addr,
-			   u32 level, struct kvm_pgtable_mm_ops *mm_ops)
+static void stage2_put_pte(const struct kvm_pgtable_visit_ctx *ctx, struct kvm_s2_mmu *mmu,
+			   struct kvm_pgtable_mm_ops *mm_ops)
 {
 	/*
 	 * Clear the existing PTE, and perform break-before-make with
 	 * TLB maintenance if it was valid.
 	 */
-	if (kvm_pte_valid(*ptep)) {
-		kvm_clear_pte(ptep);
-		kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, mmu, addr, level);
+	if (kvm_pte_valid(*ctx->ptep)) {
+		kvm_clear_pte(ctx->ptep);
+		kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, mmu, ctx->addr, ctx->level);
 	}
 
-	mm_ops->put_page(ptep);
+	mm_ops->put_page(ctx->ptep);
 }
 
 static bool stage2_pte_cacheable(struct kvm_pgtable *pgt, kvm_pte_t pte)
@@ -708,29 +710,28 @@ 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,
+static bool stage2_leaf_mapping_allowed(const struct kvm_pgtable_visit_ctx *ctx,
 					struct stage2_map_data *data)
 {
-	if (data->force_pte && (level < (KVM_PGTABLE_MAX_LEVELS - 1)))
+	if (data->force_pte && (ctx->level < (KVM_PGTABLE_MAX_LEVELS - 1)))
 		return false;
 
-	return kvm_block_mapping_supported(addr, end, data->phys, level);
+	return kvm_block_mapping_supported(ctx, data->phys);
 }
 
-static int stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level,
-				      kvm_pte_t *ptep,
+static int stage2_map_walker_try_leaf(const struct kvm_pgtable_visit_ctx *ctx,
 				      struct stage2_map_data *data)
 {
-	kvm_pte_t new, old = *ptep;
-	u64 granule = kvm_granule_size(level), phys = data->phys;
+	kvm_pte_t new, old = *ctx->ptep;
+	u64 granule = kvm_granule_size(ctx->level), phys = data->phys;
 	struct kvm_pgtable *pgt = data->mmu->pgt;
 	struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops;
 
-	if (!stage2_leaf_mapping_allowed(addr, end, level, data))
+	if (!stage2_leaf_mapping_allowed(ctx, data))
 		return -E2BIG;
 
 	if (kvm_phys_is_valid(phys))
-		new = kvm_init_valid_leaf_pte(phys, data->attr, level);
+		new = kvm_init_valid_leaf_pte(phys, data->attr, ctx->level);
 	else
 		new = kvm_init_invalid_leaf_owner(data->owner_id);
 
@@ -744,7 +745,7 @@ static int stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level,
 		if (!stage2_pte_needs_update(old, new))
 			return -EAGAIN;
 
-		stage2_put_pte(ptep, data->mmu, addr, level, mm_ops);
+		stage2_put_pte(ctx, data->mmu, mm_ops);
 	}
 
 	/* Perform CMOs before installation of the guest stage-2 PTE */
@@ -755,26 +756,25 @@ static int stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level,
 	if (mm_ops->icache_inval_pou && stage2_pte_executable(new))
 		mm_ops->icache_inval_pou(kvm_pte_follow(new, mm_ops), granule);
 
-	smp_store_release(ptep, new);
+	smp_store_release(ctx->ptep, new);
 	if (stage2_pte_is_counted(new))
-		mm_ops->get_page(ptep);
+		mm_ops->get_page(ctx->ptep);
 	if (kvm_phys_is_valid(phys))
 		data->phys += granule;
 	return 0;
 }
 
-static int stage2_map_walk_table_pre(u64 addr, u64 end, u32 level,
-				     kvm_pte_t *ptep,
+static int stage2_map_walk_table_pre(const struct kvm_pgtable_visit_ctx *ctx,
 				     struct stage2_map_data *data)
 {
 	if (data->anchor)
 		return 0;
 
-	if (!stage2_leaf_mapping_allowed(addr, end, level, data))
+	if (!stage2_leaf_mapping_allowed(ctx, data))
 		return 0;
 
-	data->childp = kvm_pte_follow(*ptep, data->mm_ops);
-	kvm_clear_pte(ptep);
+	data->childp = kvm_pte_follow(*ctx->ptep, data->mm_ops);
+	kvm_clear_pte(ctx->ptep);
 
 	/*
 	 * Invalidate the whole stage-2, as we may have numerous leaf
@@ -782,29 +782,29 @@ static int stage2_map_walk_table_pre(u64 addr, u64 end, u32 level,
 	 * individually.
 	 */
 	kvm_call_hyp(__kvm_tlb_flush_vmid, data->mmu);
-	data->anchor = ptep;
+	data->anchor = ctx->ptep;
 	return 0;
 }
 
-static int stage2_map_walk_leaf(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
+static int stage2_map_walk_leaf(const struct kvm_pgtable_visit_ctx *ctx,
 				struct stage2_map_data *data)
 {
 	struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops;
-	kvm_pte_t *childp, pte = *ptep;
+	kvm_pte_t *childp, pte = *ctx->ptep;
 	int ret;
 
 	if (data->anchor) {
 		if (stage2_pte_is_counted(pte))
-			mm_ops->put_page(ptep);
+			mm_ops->put_page(ctx->ptep);
 
 		return 0;
 	}
 
-	ret = stage2_map_walker_try_leaf(addr, end, level, ptep, data);
+	ret = stage2_map_walker_try_leaf(ctx, data);
 	if (ret != -E2BIG)
 		return ret;
 
-	if (WARN_ON(level == KVM_PGTABLE_MAX_LEVELS - 1))
+	if (WARN_ON(ctx->level == KVM_PGTABLE_MAX_LEVELS - 1))
 		return -EINVAL;
 
 	if (!data->memcache)
@@ -820,16 +820,15 @@ static int stage2_map_walk_leaf(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
 	 * will be mapped lazily.
 	 */
 	if (stage2_pte_is_counted(pte))
-		stage2_put_pte(ptep, data->mmu, addr, level, mm_ops);
+		stage2_put_pte(ctx, data->mmu, mm_ops);
 
-	kvm_set_table_pte(ptep, childp, mm_ops);
-	mm_ops->get_page(ptep);
+	kvm_set_table_pte(ctx->ptep, childp, mm_ops);
+	mm_ops->get_page(ctx->ptep);
 
 	return 0;
 }
 
-static int stage2_map_walk_table_post(u64 addr, u64 end, u32 level,
-				      kvm_pte_t *ptep,
+static int stage2_map_walk_table_post(const struct kvm_pgtable_visit_ctx *ctx,
 				      struct stage2_map_data *data)
 {
 	struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops;
@@ -839,17 +838,17 @@ static int stage2_map_walk_table_post(u64 addr, u64 end, u32 level,
 	if (!data->anchor)
 		return 0;
 
-	if (data->anchor == ptep) {
+	if (data->anchor == ctx->ptep) {
 		childp = data->childp;
 		data->anchor = NULL;
 		data->childp = NULL;
-		ret = stage2_map_walk_leaf(addr, end, level, ptep, data);
+		ret = stage2_map_walk_leaf(ctx, data);
 	} else {
-		childp = kvm_pte_follow(*ptep, mm_ops);
+		childp = kvm_pte_follow(*ctx->ptep, mm_ops);
 	}
 
 	mm_ops->put_page(childp);
-	mm_ops->put_page(ptep);
+	mm_ops->put_page(ctx->ptep);
 
 	return ret;
 }
@@ -873,18 +872,18 @@ static int stage2_map_walk_table_post(u64 addr, u64 end, u32 level,
  * the page-table, installing the block entry when it revisits the anchor
  * pointer and clearing the anchor to NULL.
  */
-static int stage2_map_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
-			     enum kvm_pgtable_walk_flags flag, void * const arg)
+static int stage2_map_walker(const struct kvm_pgtable_visit_ctx *ctx,
+			     enum kvm_pgtable_walk_flags visit)
 {
-	struct stage2_map_data *data = arg;
+	struct stage2_map_data *data = ctx->arg;
 
-	switch (flag) {
+	switch (visit) {
 	case KVM_PGTABLE_WALK_TABLE_PRE:
-		return stage2_map_walk_table_pre(addr, end, level, ptep, data);
+		return stage2_map_walk_table_pre(ctx, data);
 	case KVM_PGTABLE_WALK_LEAF:
-		return stage2_map_walk_leaf(addr, end, level, ptep, data);
+		return stage2_map_walk_leaf(ctx, data);
 	case KVM_PGTABLE_WALK_TABLE_POST:
-		return stage2_map_walk_table_post(addr, end, level, ptep, data);
+		return stage2_map_walk_table_post(ctx, data);
 	}
 
 	return -EINVAL;
@@ -949,25 +948,24 @@ int kvm_pgtable_stage2_set_owner(struct kvm_pgtable *pgt, u64 addr, u64 size,
 	return ret;
 }
 
-static int stage2_unmap_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
-			       enum kvm_pgtable_walk_flags flag,
-			       void * const arg)
+static int stage2_unmap_walker(const struct kvm_pgtable_visit_ctx *ctx,
+			       enum kvm_pgtable_walk_flags visit)
 {
-	struct kvm_pgtable *pgt = arg;
+	struct kvm_pgtable *pgt = ctx->arg;
 	struct kvm_s2_mmu *mmu = pgt->mmu;
 	struct kvm_pgtable_mm_ops *mm_ops = pgt->mm_ops;
-	kvm_pte_t pte = *ptep, *childp = NULL;
+	kvm_pte_t pte = *ctx->ptep, *childp = NULL;
 	bool need_flush = false;
 
 	if (!kvm_pte_valid(pte)) {
 		if (stage2_pte_is_counted(pte)) {
-			kvm_clear_pte(ptep);
-			mm_ops->put_page(ptep);
+			kvm_clear_pte(ctx->ptep);
+			mm_ops->put_page(ctx->ptep);
 		}
 		return 0;
 	}
 
-	if (kvm_pte_table(pte, level)) {
+	if (kvm_pte_table(pte, ctx->level)) {
 		childp = kvm_pte_follow(pte, mm_ops);
 
 		if (mm_ops->page_count(childp) != 1)
@@ -981,11 +979,11 @@ static int stage2_unmap_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
 	 * block entry and rely on the remaining portions being faulted
 	 * back lazily.
 	 */
-	stage2_put_pte(ptep, mmu, addr, level, mm_ops);
+	stage2_put_pte(ctx, mmu, mm_ops);
 
 	if (need_flush && mm_ops->dcache_clean_inval_poc)
 		mm_ops->dcache_clean_inval_poc(kvm_pte_follow(pte, mm_ops),
-					       kvm_granule_size(level));
+					       kvm_granule_size(ctx->level));
 
 	if (childp)
 		mm_ops->put_page(childp);
@@ -1012,18 +1010,17 @@ struct stage2_attr_data {
 	struct kvm_pgtable_mm_ops	*mm_ops;
 };
 
-static int stage2_attr_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
-			      enum kvm_pgtable_walk_flags flag,
-			      void * const arg)
+static int stage2_attr_walker(const struct kvm_pgtable_visit_ctx *ctx,
+			      enum kvm_pgtable_walk_flags visit)
 {
-	kvm_pte_t pte = *ptep;
-	struct stage2_attr_data *data = arg;
+	kvm_pte_t pte = *ctx->ptep;
+	struct stage2_attr_data *data = ctx->arg;
 	struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops;
 
 	if (!kvm_pte_valid(pte))
 		return 0;
 
-	data->level = level;
+	data->level = ctx->level;
 	data->pte = pte;
 	pte &= ~data->attr_clr;
 	pte |= data->attr_set;
@@ -1039,10 +1036,10 @@ static int stage2_attr_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
 		 * stage-2 PTE if we are going to add executable permission.
 		 */
 		if (mm_ops->icache_inval_pou &&
-		    stage2_pte_executable(pte) && !stage2_pte_executable(*ptep))
+		    stage2_pte_executable(pte) && !stage2_pte_executable(*ctx->ptep))
 			mm_ops->icache_inval_pou(kvm_pte_follow(pte, mm_ops),
-						  kvm_granule_size(level));
-		WRITE_ONCE(*ptep, pte);
+						  kvm_granule_size(ctx->level));
+		WRITE_ONCE(*ctx->ptep, pte);
 	}
 
 	return 0;
@@ -1140,20 +1137,19 @@ int kvm_pgtable_stage2_relax_perms(struct kvm_pgtable *pgt, u64 addr,
 	return ret;
 }
 
-static int stage2_flush_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
-			       enum kvm_pgtable_walk_flags flag,
-			       void * const arg)
+static int stage2_flush_walker(const struct kvm_pgtable_visit_ctx *ctx,
+			       enum kvm_pgtable_walk_flags visit)
 {
-	struct kvm_pgtable *pgt = arg;
+	struct kvm_pgtable *pgt = ctx->arg;
 	struct kvm_pgtable_mm_ops *mm_ops = pgt->mm_ops;
-	kvm_pte_t pte = *ptep;
+	kvm_pte_t pte = *ctx->ptep;
 
 	if (!kvm_pte_valid(pte) || !stage2_pte_cacheable(pgt, pte))
 		return 0;
 
 	if (mm_ops->dcache_clean_inval_poc)
 		mm_ops->dcache_clean_inval_poc(kvm_pte_follow(pte, mm_ops),
-					       kvm_granule_size(level));
+					       kvm_granule_size(ctx->level));
 	return 0;
 }
 
@@ -1200,19 +1196,18 @@ int __kvm_pgtable_stage2_init(struct kvm_pgtable *pgt, struct kvm_s2_mmu *mmu,
 	return 0;
 }
 
-static int stage2_free_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
-			      enum kvm_pgtable_walk_flags flag,
-			      void * const arg)
+static int stage2_free_walker(const struct kvm_pgtable_visit_ctx *ctx,
+			      enum kvm_pgtable_walk_flags visit)
 {
-	struct kvm_pgtable_mm_ops *mm_ops = arg;
-	kvm_pte_t pte = *ptep;
+	struct kvm_pgtable_mm_ops *mm_ops = ctx->arg;
+	kvm_pte_t pte = *ctx->ptep;
 
 	if (!stage2_pte_is_counted(pte))
 		return 0;
 
-	mm_ops->put_page(ptep);
+	mm_ops->put_page(ctx->ptep);
 
-	if (kvm_pte_table(pte, level))
+	if (kvm_pte_table(pte, ctx->level))
 		mm_ops->put_page(kvm_pte_follow(pte, mm_ops));
 
 	return 0;
-- 
2.38.1.273.g43a17bfeac-goog


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH v3 02/15] KVM: arm64: Stash observed pte value in visitor context

[Oliver Upton]

Rather than reading the ptep all over the shop, read the ptep once from
__kvm_pgtable_visit() and stick it in the visitor context. Reread the
ptep after visiting a leaf in case the callback installed a new table
underneath.

No functional change intended.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/include/asm/kvm_pgtable.h  |  1 +
 arch/arm64/kvm/hyp/nvhe/mem_protect.c |  5 +-
 arch/arm64/kvm/hyp/nvhe/setup.c       |  7 +--
 arch/arm64/kvm/hyp/pgtable.c          | 86 +++++++++++++--------------
 4 files changed, 48 insertions(+), 51 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 607f9bb8aab4..14d4b68a1e92 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -201,6 +201,7 @@ enum kvm_pgtable_walk_flags {
 
 struct kvm_pgtable_visit_ctx {
 	kvm_pte_t				*ptep;
+	kvm_pte_t				old;
 	void					*arg;
 	u64					addr;
 	u64					end;
diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index 8f5b6a36a039..d21d1b08a055 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -421,12 +421,11 @@ static int __check_page_state_visitor(const struct kvm_pgtable_visit_ctx *ctx,
 				      enum kvm_pgtable_walk_flags visit)
 {
 	struct check_walk_data *d = ctx->arg;
-	kvm_pte_t pte = *ctx->ptep;
 
-	if (kvm_pte_valid(pte) && !addr_is_memory(kvm_pte_to_phys(pte)))
+	if (kvm_pte_valid(ctx->old) && !addr_is_memory(kvm_pte_to_phys(ctx->old)))
 		return -EINVAL;
 
-	return d->get_page_state(pte) == d->desired ? 0 : -EPERM;
+	return d->get_page_state(ctx->old) == d->desired ? 0 : -EPERM;
 }
 
 static int check_page_state_range(struct kvm_pgtable *pgt, u64 addr, u64 size,
diff --git a/arch/arm64/kvm/hyp/nvhe/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
index a293cf5eba1b..6af443c9d78e 100644
--- a/arch/arm64/kvm/hyp/nvhe/setup.c
+++ b/arch/arm64/kvm/hyp/nvhe/setup.c
@@ -192,10 +192,9 @@ static int finalize_host_mappings_walker(const struct kvm_pgtable_visit_ctx *ctx
 	struct kvm_pgtable_mm_ops *mm_ops = ctx->arg;
 	enum kvm_pgtable_prot prot;
 	enum pkvm_page_state state;
-	kvm_pte_t pte = *ctx->ptep;
 	phys_addr_t phys;
 
-	if (!kvm_pte_valid(pte))
+	if (!kvm_pte_valid(ctx->old))
 		return 0;
 
 	/*
@@ -210,7 +209,7 @@ static int finalize_host_mappings_walker(const struct kvm_pgtable_visit_ctx *ctx
 	if (ctx->level != (KVM_PGTABLE_MAX_LEVELS - 1))
 		return -EINVAL;
 
-	phys = kvm_pte_to_phys(pte);
+	phys = kvm_pte_to_phys(ctx->old);
 	if (!addr_is_memory(phys))
 		return -EINVAL;
 
@@ -218,7 +217,7 @@ static int finalize_host_mappings_walker(const struct kvm_pgtable_visit_ctx *ctx
 	 * Adjust the host stage-2 mappings to match the ownership attributes
 	 * configured in the hypervisor stage-1.
 	 */
-	state = pkvm_getstate(kvm_pgtable_hyp_pte_prot(pte));
+	state = pkvm_getstate(kvm_pgtable_hyp_pte_prot(ctx->old));
 	switch (state) {
 	case PKVM_PAGE_OWNED:
 		return host_stage2_set_owner_locked(phys, PAGE_SIZE, pkvm_hyp_id);
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 900c8b9c0cfc..fb3696b3a997 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -189,6 +189,7 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
 	enum kvm_pgtable_walk_flags flags = data->walker->flags;
 	struct kvm_pgtable_visit_ctx ctx = {
 		.ptep	= ptep,
+		.old	= READ_ONCE(*ptep),
 		.arg	= data->walker->arg,
 		.addr	= data->addr,
 		.end	= data->end,
@@ -196,16 +197,16 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
 		.flags	= flags,
 	};
 	int ret = 0;
-	kvm_pte_t *childp, pte = *ptep;
-	bool table = kvm_pte_table(pte, level);
+	kvm_pte_t *childp;
+	bool table = kvm_pte_table(ctx.old, level);
 
 	if (table && (ctx.flags & KVM_PGTABLE_WALK_TABLE_PRE))
 		ret = kvm_pgtable_visitor_cb(data, &ctx, KVM_PGTABLE_WALK_TABLE_PRE);
 
 	if (!table && (ctx.flags & KVM_PGTABLE_WALK_LEAF)) {
 		ret = kvm_pgtable_visitor_cb(data, &ctx, KVM_PGTABLE_WALK_LEAF);
-		pte = *ptep;
-		table = kvm_pte_table(pte, level);
+		ctx.old = READ_ONCE(*ptep);
+		table = kvm_pte_table(ctx.old, level);
 	}
 
 	if (ret)
@@ -217,7 +218,7 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
 		goto out;
 	}
 
-	childp = kvm_pte_follow(pte, data->pgt->mm_ops);
+	childp = kvm_pte_follow(ctx.old, data->pgt->mm_ops);
 	ret = __kvm_pgtable_walk(data, childp, level + 1);
 	if (ret)
 		goto out;
@@ -299,7 +300,7 @@ static int leaf_walker(const struct kvm_pgtable_visit_ctx *ctx,
 {
 	struct leaf_walk_data *data = ctx->arg;
 
-	data->pte   = *ctx->ptep;
+	data->pte   = ctx->old;
 	data->level = ctx->level;
 
 	return 0;
@@ -388,7 +389,7 @@ enum kvm_pgtable_prot kvm_pgtable_hyp_pte_prot(kvm_pte_t pte)
 static bool hyp_map_walker_try_leaf(const struct kvm_pgtable_visit_ctx *ctx,
 				    struct hyp_map_data *data)
 {
-	kvm_pte_t new, old = *ctx->ptep;
+	kvm_pte_t new;
 	u64 granule = kvm_granule_size(ctx->level), phys = data->phys;
 
 	if (!kvm_block_mapping_supported(ctx, phys))
@@ -396,11 +397,11 @@ static bool hyp_map_walker_try_leaf(const struct kvm_pgtable_visit_ctx *ctx,
 
 	data->phys += granule;
 	new = kvm_init_valid_leaf_pte(phys, data->attr, ctx->level);
-	if (old == new)
+	if (ctx->old == new)
 		return true;
-	if (!kvm_pte_valid(old))
+	if (!kvm_pte_valid(ctx->old))
 		data->mm_ops->get_page(ctx->ptep);
-	else if (WARN_ON((old ^ new) & ~KVM_PTE_LEAF_ATTR_HI_SW))
+	else if (WARN_ON((ctx->old ^ new) & ~KVM_PTE_LEAF_ATTR_HI_SW))
 		return false;
 
 	smp_store_release(ctx->ptep, new);
@@ -461,16 +462,16 @@ struct hyp_unmap_data {
 static int hyp_unmap_walker(const struct kvm_pgtable_visit_ctx *ctx,
 			    enum kvm_pgtable_walk_flags visit)
 {
-	kvm_pte_t pte = *ctx->ptep, *childp = NULL;
+	kvm_pte_t *childp = NULL;
 	u64 granule = kvm_granule_size(ctx->level);
 	struct hyp_unmap_data *data = ctx->arg;
 	struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops;
 
-	if (!kvm_pte_valid(pte))
+	if (!kvm_pte_valid(ctx->old))
 		return -EINVAL;
 
-	if (kvm_pte_table(pte, ctx->level)) {
-		childp = kvm_pte_follow(pte, mm_ops);
+	if (kvm_pte_table(ctx->old, ctx->level)) {
+		childp = kvm_pte_follow(ctx->old, mm_ops);
 
 		if (mm_ops->page_count(childp) != 1)
 			return 0;
@@ -538,15 +539,14 @@ static int hyp_free_walker(const struct kvm_pgtable_visit_ctx *ctx,
 			   enum kvm_pgtable_walk_flags visit)
 {
 	struct kvm_pgtable_mm_ops *mm_ops = ctx->arg;
-	kvm_pte_t pte = *ctx->ptep;
 
-	if (!kvm_pte_valid(pte))
+	if (!kvm_pte_valid(ctx->old))
 		return 0;
 
 	mm_ops->put_page(ctx->ptep);
 
-	if (kvm_pte_table(pte, ctx->level))
-		mm_ops->put_page(kvm_pte_follow(pte, mm_ops));
+	if (kvm_pte_table(ctx->old, ctx->level))
+		mm_ops->put_page(kvm_pte_follow(ctx->old, mm_ops));
 
 	return 0;
 }
@@ -691,7 +691,7 @@ static void stage2_put_pte(const struct kvm_pgtable_visit_ctx *ctx, struct kvm_s
 	 * Clear the existing PTE, and perform break-before-make with
 	 * TLB maintenance if it was valid.
 	 */
-	if (kvm_pte_valid(*ctx->ptep)) {
+	if (kvm_pte_valid(ctx->old)) {
 		kvm_clear_pte(ctx->ptep);
 		kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, mmu, ctx->addr, ctx->level);
 	}
@@ -722,7 +722,7 @@ static bool stage2_leaf_mapping_allowed(const struct kvm_pgtable_visit_ctx *ctx,
 static int stage2_map_walker_try_leaf(const struct kvm_pgtable_visit_ctx *ctx,
 				      struct stage2_map_data *data)
 {
-	kvm_pte_t new, old = *ctx->ptep;
+	kvm_pte_t new;
 	u64 granule = kvm_granule_size(ctx->level), phys = data->phys;
 	struct kvm_pgtable *pgt = data->mmu->pgt;
 	struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops;
@@ -735,14 +735,14 @@ static int stage2_map_walker_try_leaf(const struct kvm_pgtable_visit_ctx *ctx,
 	else
 		new = kvm_init_invalid_leaf_owner(data->owner_id);
 
-	if (stage2_pte_is_counted(old)) {
+	if (stage2_pte_is_counted(ctx->old)) {
 		/*
 		 * Skip updating the PTE if we are trying to recreate the exact
 		 * same mapping or only change the access permissions. Instead,
 		 * the vCPU will exit one more time from guest if still needed
 		 * and then go through the path of relaxing permissions.
 		 */
-		if (!stage2_pte_needs_update(old, new))
+		if (!stage2_pte_needs_update(ctx->old, new))
 			return -EAGAIN;
 
 		stage2_put_pte(ctx, data->mmu, mm_ops);
@@ -773,7 +773,7 @@ static int stage2_map_walk_table_pre(const struct kvm_pgtable_visit_ctx *ctx,
 	if (!stage2_leaf_mapping_allowed(ctx, data))
 		return 0;
 
-	data->childp = kvm_pte_follow(*ctx->ptep, data->mm_ops);
+	data->childp = kvm_pte_follow(ctx->old, data->mm_ops);
 	kvm_clear_pte(ctx->ptep);
 
 	/*
@@ -790,11 +790,11 @@ static int stage2_map_walk_leaf(const struct kvm_pgtable_visit_ctx *ctx,
 				struct stage2_map_data *data)
 {
 	struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops;
-	kvm_pte_t *childp, pte = *ctx->ptep;
+	kvm_pte_t *childp;
 	int ret;
 
 	if (data->anchor) {
-		if (stage2_pte_is_counted(pte))
+		if (stage2_pte_is_counted(ctx->old))
 			mm_ops->put_page(ctx->ptep);
 
 		return 0;
@@ -819,7 +819,7 @@ static int stage2_map_walk_leaf(const struct kvm_pgtable_visit_ctx *ctx,
 	 * a table. Accesses beyond 'end' that fall within the new table
 	 * will be mapped lazily.
 	 */
-	if (stage2_pte_is_counted(pte))
+	if (stage2_pte_is_counted(ctx->old))
 		stage2_put_pte(ctx, data->mmu, mm_ops);
 
 	kvm_set_table_pte(ctx->ptep, childp, mm_ops);
@@ -844,7 +844,7 @@ static int stage2_map_walk_table_post(const struct kvm_pgtable_visit_ctx *ctx,
 		data->childp = NULL;
 		ret = stage2_map_walk_leaf(ctx, data);
 	} else {
-		childp = kvm_pte_follow(*ctx->ptep, mm_ops);
+		childp = kvm_pte_follow(ctx->old, mm_ops);
 	}
 
 	mm_ops->put_page(childp);
@@ -954,23 +954,23 @@ static int stage2_unmap_walker(const struct kvm_pgtable_visit_ctx *ctx,
 	struct kvm_pgtable *pgt = ctx->arg;
 	struct kvm_s2_mmu *mmu = pgt->mmu;
 	struct kvm_pgtable_mm_ops *mm_ops = pgt->mm_ops;
-	kvm_pte_t pte = *ctx->ptep, *childp = NULL;
+	kvm_pte_t *childp = NULL;
 	bool need_flush = false;
 
-	if (!kvm_pte_valid(pte)) {
-		if (stage2_pte_is_counted(pte)) {
+	if (!kvm_pte_valid(ctx->old)) {
+		if (stage2_pte_is_counted(ctx->old)) {
 			kvm_clear_pte(ctx->ptep);
 			mm_ops->put_page(ctx->ptep);
 		}
 		return 0;
 	}
 
-	if (kvm_pte_table(pte, ctx->level)) {
-		childp = kvm_pte_follow(pte, mm_ops);
+	if (kvm_pte_table(ctx->old, ctx->level)) {
+		childp = kvm_pte_follow(ctx->old, mm_ops);
 
 		if (mm_ops->page_count(childp) != 1)
 			return 0;
-	} else if (stage2_pte_cacheable(pgt, pte)) {
+	} else if (stage2_pte_cacheable(pgt, ctx->old)) {
 		need_flush = !stage2_has_fwb(pgt);
 	}
 
@@ -982,7 +982,7 @@ static int stage2_unmap_walker(const struct kvm_pgtable_visit_ctx *ctx,
 	stage2_put_pte(ctx, mmu, mm_ops);
 
 	if (need_flush && mm_ops->dcache_clean_inval_poc)
-		mm_ops->dcache_clean_inval_poc(kvm_pte_follow(pte, mm_ops),
+		mm_ops->dcache_clean_inval_poc(kvm_pte_follow(ctx->old, mm_ops),
 					       kvm_granule_size(ctx->level));
 
 	if (childp)
@@ -1013,11 +1013,11 @@ struct stage2_attr_data {
 static int stage2_attr_walker(const struct kvm_pgtable_visit_ctx *ctx,
 			      enum kvm_pgtable_walk_flags visit)
 {
-	kvm_pte_t pte = *ctx->ptep;
+	kvm_pte_t pte = ctx->old;
 	struct stage2_attr_data *data = ctx->arg;
 	struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops;
 
-	if (!kvm_pte_valid(pte))
+	if (!kvm_pte_valid(ctx->old))
 		return 0;
 
 	data->level = ctx->level;
@@ -1036,7 +1036,7 @@ static int stage2_attr_walker(const struct kvm_pgtable_visit_ctx *ctx,
 		 * stage-2 PTE if we are going to add executable permission.
 		 */
 		if (mm_ops->icache_inval_pou &&
-		    stage2_pte_executable(pte) && !stage2_pte_executable(*ctx->ptep))
+		    stage2_pte_executable(pte) && !stage2_pte_executable(ctx->old))
 			mm_ops->icache_inval_pou(kvm_pte_follow(pte, mm_ops),
 						  kvm_granule_size(ctx->level));
 		WRITE_ONCE(*ctx->ptep, pte);
@@ -1142,13 +1142,12 @@ static int stage2_flush_walker(const struct kvm_pgtable_visit_ctx *ctx,
 {
 	struct kvm_pgtable *pgt = ctx->arg;
 	struct kvm_pgtable_mm_ops *mm_ops = pgt->mm_ops;
-	kvm_pte_t pte = *ctx->ptep;
 
-	if (!kvm_pte_valid(pte) || !stage2_pte_cacheable(pgt, pte))
+	if (!kvm_pte_valid(ctx->old) || !stage2_pte_cacheable(pgt, ctx->old))
 		return 0;
 
 	if (mm_ops->dcache_clean_inval_poc)
-		mm_ops->dcache_clean_inval_poc(kvm_pte_follow(pte, mm_ops),
+		mm_ops->dcache_clean_inval_poc(kvm_pte_follow(ctx->old, mm_ops),
 					       kvm_granule_size(ctx->level));
 	return 0;
 }
@@ -1200,15 +1199,14 @@ static int stage2_free_walker(const struct kvm_pgtable_visit_ctx *ctx,
 			      enum kvm_pgtable_walk_flags visit)
 {
 	struct kvm_pgtable_mm_ops *mm_ops = ctx->arg;
-	kvm_pte_t pte = *ctx->ptep;
 
-	if (!stage2_pte_is_counted(pte))
+	if (!stage2_pte_is_counted(ctx->old))
 		return 0;
 
 	mm_ops->put_page(ctx->ptep);
 
-	if (kvm_pte_table(pte, ctx->level))
-		mm_ops->put_page(kvm_pte_follow(pte, mm_ops));
+	if (kvm_pte_table(ctx->old, ctx->level))
+		mm_ops->put_page(kvm_pte_follow(ctx->old, mm_ops));
 
 	return 0;
 }
-- 
2.38.1.273.g43a17bfeac-goog


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH v3 03/15] KVM: arm64: Pass mm_ops through the visitor context

[Oliver Upton]

As a prerequisite for getting visitors off of struct kvm_pgtable, pass
mm_ops through the visitor context.

No functional change intended.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/include/asm/kvm_pgtable.h |  1 +
 arch/arm64/kvm/hyp/nvhe/setup.c      |  3 +-
 arch/arm64/kvm/hyp/pgtable.c         | 63 +++++++++++-----------------
 3 files changed, 26 insertions(+), 41 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 14d4b68a1e92..a752793482cb 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -203,6 +203,7 @@ struct kvm_pgtable_visit_ctx {
 	kvm_pte_t				*ptep;
 	kvm_pte_t				old;
 	void					*arg;
+	struct kvm_pgtable_mm_ops		*mm_ops;
 	u64					addr;
 	u64					end;
 	u32					level;
diff --git a/arch/arm64/kvm/hyp/nvhe/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
index 6af443c9d78e..1068338d77f3 100644
--- a/arch/arm64/kvm/hyp/nvhe/setup.c
+++ b/arch/arm64/kvm/hyp/nvhe/setup.c
@@ -189,7 +189,7 @@ static void hpool_put_page(void *addr)
 static int finalize_host_mappings_walker(const struct kvm_pgtable_visit_ctx *ctx,
 					 enum kvm_pgtable_walk_flags visit)
 {
-	struct kvm_pgtable_mm_ops *mm_ops = ctx->arg;
+	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
 	enum kvm_pgtable_prot prot;
 	enum pkvm_page_state state;
 	phys_addr_t phys;
@@ -239,7 +239,6 @@ static int finalize_host_mappings(void)
 	struct kvm_pgtable_walker walker = {
 		.cb	= finalize_host_mappings_walker,
 		.flags	= KVM_PGTABLE_WALK_LEAF | KVM_PGTABLE_WALK_TABLE_POST,
-		.arg	= pkvm_pgtable.mm_ops,
 	};
 	int i, ret;
 
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index fb3696b3a997..db25e81a9890 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -181,9 +181,10 @@ static int kvm_pgtable_visitor_cb(struct kvm_pgtable_walk_data *data,
 }
 
 static int __kvm_pgtable_walk(struct kvm_pgtable_walk_data *data,
-			      kvm_pte_t *pgtable, u32 level);
+			      struct kvm_pgtable_mm_ops *mm_ops, kvm_pte_t *pgtable, u32 level);
 
 static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
+				      struct kvm_pgtable_mm_ops *mm_ops,
 				      kvm_pte_t *ptep, u32 level)
 {
 	enum kvm_pgtable_walk_flags flags = data->walker->flags;
@@ -191,6 +192,7 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
 		.ptep	= ptep,
 		.old	= READ_ONCE(*ptep),
 		.arg	= data->walker->arg,
+		.mm_ops	= mm_ops,
 		.addr	= data->addr,
 		.end	= data->end,
 		.level	= level,
@@ -218,8 +220,8 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
 		goto out;
 	}
 
-	childp = kvm_pte_follow(ctx.old, data->pgt->mm_ops);
-	ret = __kvm_pgtable_walk(data, childp, level + 1);
+	childp = kvm_pte_follow(ctx.old, mm_ops);
+	ret = __kvm_pgtable_walk(data, mm_ops, childp, level + 1);
 	if (ret)
 		goto out;
 
@@ -231,7 +233,7 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
 }
 
 static int __kvm_pgtable_walk(struct kvm_pgtable_walk_data *data,
-			      kvm_pte_t *pgtable, u32 level)
+			      struct kvm_pgtable_mm_ops *mm_ops, kvm_pte_t *pgtable, u32 level)
 {
 	u32 idx;
 	int ret = 0;
@@ -245,7 +247,7 @@ static int __kvm_pgtable_walk(struct kvm_pgtable_walk_data *data,
 		if (data->addr >= data->end)
 			break;
 
-		ret = __kvm_pgtable_visit(data, ptep, level);
+		ret = __kvm_pgtable_visit(data, mm_ops, ptep, level);
 		if (ret)
 			break;
 	}
@@ -269,7 +271,7 @@ static int _kvm_pgtable_walk(struct kvm_pgtable_walk_data *data)
 	for (idx = kvm_pgd_page_idx(data); data->addr < data->end; ++idx) {
 		kvm_pte_t *ptep = &pgt->pgd[idx * PTRS_PER_PTE];
 
-		ret = __kvm_pgtable_walk(data, ptep, pgt->start_level);
+		ret = __kvm_pgtable_walk(data, pgt->mm_ops, ptep, pgt->start_level);
 		if (ret)
 			break;
 	}
@@ -332,7 +334,6 @@ int kvm_pgtable_get_leaf(struct kvm_pgtable *pgt, u64 addr,
 struct hyp_map_data {
 	u64				phys;
 	kvm_pte_t			attr;
-	struct kvm_pgtable_mm_ops	*mm_ops;
 };
 
 static int hyp_set_prot_attr(enum kvm_pgtable_prot prot, kvm_pte_t *ptep)
@@ -400,7 +401,7 @@ static bool hyp_map_walker_try_leaf(const struct kvm_pgtable_visit_ctx *ctx,
 	if (ctx->old == new)
 		return true;
 	if (!kvm_pte_valid(ctx->old))
-		data->mm_ops->get_page(ctx->ptep);
+		ctx->mm_ops->get_page(ctx->ptep);
 	else if (WARN_ON((ctx->old ^ new) & ~KVM_PTE_LEAF_ATTR_HI_SW))
 		return false;
 
@@ -413,7 +414,7 @@ static int hyp_map_walker(const struct kvm_pgtable_visit_ctx *ctx,
 {
 	kvm_pte_t *childp;
 	struct hyp_map_data *data = ctx->arg;
-	struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops;
+	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
 
 	if (hyp_map_walker_try_leaf(ctx, data))
 		return 0;
@@ -436,7 +437,6 @@ int kvm_pgtable_hyp_map(struct kvm_pgtable *pgt, u64 addr, u64 size, u64 phys,
 	int ret;
 	struct hyp_map_data map_data = {
 		.phys	= ALIGN_DOWN(phys, PAGE_SIZE),
-		.mm_ops	= pgt->mm_ops,
 	};
 	struct kvm_pgtable_walker walker = {
 		.cb	= hyp_map_walker,
@@ -454,18 +454,13 @@ int kvm_pgtable_hyp_map(struct kvm_pgtable *pgt, u64 addr, u64 size, u64 phys,
 	return ret;
 }
 
-struct hyp_unmap_data {
-	u64				unmapped;
-	struct kvm_pgtable_mm_ops	*mm_ops;
-};
-
 static int hyp_unmap_walker(const struct kvm_pgtable_visit_ctx *ctx,
 			    enum kvm_pgtable_walk_flags visit)
 {
 	kvm_pte_t *childp = NULL;
 	u64 granule = kvm_granule_size(ctx->level);
-	struct hyp_unmap_data *data = ctx->arg;
-	struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops;
+	u64 *unmapped = ctx->arg;
+	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
 
 	if (!kvm_pte_valid(ctx->old))
 		return -EINVAL;
@@ -486,7 +481,7 @@ static int hyp_unmap_walker(const struct kvm_pgtable_visit_ctx *ctx,
 		kvm_clear_pte(ctx->ptep);
 		dsb(ishst);
 		__tlbi_level(vale2is, __TLBI_VADDR(ctx->addr, 0), ctx->level);
-		data->unmapped += granule;
+		*unmapped += granule;
 	}
 
 	dsb(ish);
@@ -501,12 +496,10 @@ static int hyp_unmap_walker(const struct kvm_pgtable_visit_ctx *ctx,
 
 u64 kvm_pgtable_hyp_unmap(struct kvm_pgtable *pgt, u64 addr, u64 size)
 {
-	struct hyp_unmap_data unmap_data = {
-		.mm_ops	= pgt->mm_ops,
-	};
+	u64 unmapped = 0;
 	struct kvm_pgtable_walker walker = {
 		.cb	= hyp_unmap_walker,
-		.arg	= &unmap_data,
+		.arg	= &unmapped,
 		.flags	= KVM_PGTABLE_WALK_LEAF | KVM_PGTABLE_WALK_TABLE_POST,
 	};
 
@@ -514,7 +507,7 @@ u64 kvm_pgtable_hyp_unmap(struct kvm_pgtable *pgt, u64 addr, u64 size)
 		return 0;
 
 	kvm_pgtable_walk(pgt, addr, size, &walker);
-	return unmap_data.unmapped;
+	return unmapped;
 }
 
 int kvm_pgtable_hyp_init(struct kvm_pgtable *pgt, u32 va_bits,
@@ -538,7 +531,7 @@ int kvm_pgtable_hyp_init(struct kvm_pgtable *pgt, u32 va_bits,
 static int hyp_free_walker(const struct kvm_pgtable_visit_ctx *ctx,
 			   enum kvm_pgtable_walk_flags visit)
 {
-	struct kvm_pgtable_mm_ops *mm_ops = ctx->arg;
+	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
 
 	if (!kvm_pte_valid(ctx->old))
 		return 0;
@@ -556,7 +549,6 @@ void kvm_pgtable_hyp_destroy(struct kvm_pgtable *pgt)
 	struct kvm_pgtable_walker walker = {
 		.cb	= hyp_free_walker,
 		.flags	= KVM_PGTABLE_WALK_LEAF | KVM_PGTABLE_WALK_TABLE_POST,
-		.arg	= pgt->mm_ops,
 	};
 
 	WARN_ON(kvm_pgtable_walk(pgt, 0, BIT(pgt->ia_bits), &walker));
@@ -575,8 +567,6 @@ struct stage2_map_data {
 	struct kvm_s2_mmu		*mmu;
 	void				*memcache;
 
-	struct kvm_pgtable_mm_ops	*mm_ops;
-
 	/* Force mappings to page granularity */
 	bool				force_pte;
 };
@@ -725,7 +715,7 @@ static int stage2_map_walker_try_leaf(const struct kvm_pgtable_visit_ctx *ctx,
 	kvm_pte_t new;
 	u64 granule = kvm_granule_size(ctx->level), phys = data->phys;
 	struct kvm_pgtable *pgt = data->mmu->pgt;
-	struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops;
+	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
 
 	if (!stage2_leaf_mapping_allowed(ctx, data))
 		return -E2BIG;
@@ -773,7 +763,7 @@ static int stage2_map_walk_table_pre(const struct kvm_pgtable_visit_ctx *ctx,
 	if (!stage2_leaf_mapping_allowed(ctx, data))
 		return 0;
 
-	data->childp = kvm_pte_follow(ctx->old, data->mm_ops);
+	data->childp = kvm_pte_follow(ctx->old, ctx->mm_ops);
 	kvm_clear_pte(ctx->ptep);
 
 	/*
@@ -789,7 +779,7 @@ static int stage2_map_walk_table_pre(const struct kvm_pgtable_visit_ctx *ctx,
 static int stage2_map_walk_leaf(const struct kvm_pgtable_visit_ctx *ctx,
 				struct stage2_map_data *data)
 {
-	struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops;
+	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
 	kvm_pte_t *childp;
 	int ret;
 
@@ -831,7 +821,7 @@ static int stage2_map_walk_leaf(const struct kvm_pgtable_visit_ctx *ctx,
 static int stage2_map_walk_table_post(const struct kvm_pgtable_visit_ctx *ctx,
 				      struct stage2_map_data *data)
 {
-	struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops;
+	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
 	kvm_pte_t *childp;
 	int ret = 0;
 
@@ -898,7 +888,6 @@ int kvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size,
 		.phys		= ALIGN_DOWN(phys, PAGE_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 = {
@@ -929,7 +918,6 @@ int kvm_pgtable_stage2_set_owner(struct kvm_pgtable *pgt, u64 addr, u64 size,
 		.phys		= KVM_PHYS_INVALID,
 		.mmu		= pgt->mmu,
 		.memcache	= mc,
-		.mm_ops		= pgt->mm_ops,
 		.owner_id	= owner_id,
 		.force_pte	= true,
 	};
@@ -953,7 +941,7 @@ static int stage2_unmap_walker(const struct kvm_pgtable_visit_ctx *ctx,
 {
 	struct kvm_pgtable *pgt = ctx->arg;
 	struct kvm_s2_mmu *mmu = pgt->mmu;
-	struct kvm_pgtable_mm_ops *mm_ops = pgt->mm_ops;
+	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
 	kvm_pte_t *childp = NULL;
 	bool need_flush = false;
 
@@ -1007,7 +995,6 @@ struct stage2_attr_data {
 	kvm_pte_t			attr_clr;
 	kvm_pte_t			pte;
 	u32				level;
-	struct kvm_pgtable_mm_ops	*mm_ops;
 };
 
 static int stage2_attr_walker(const struct kvm_pgtable_visit_ctx *ctx,
@@ -1015,7 +1002,7 @@ static int stage2_attr_walker(const struct kvm_pgtable_visit_ctx *ctx,
 {
 	kvm_pte_t pte = ctx->old;
 	struct stage2_attr_data *data = ctx->arg;
-	struct kvm_pgtable_mm_ops *mm_ops = data->mm_ops;
+	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
 
 	if (!kvm_pte_valid(ctx->old))
 		return 0;
@@ -1055,7 +1042,6 @@ static int stage2_update_leaf_attrs(struct kvm_pgtable *pgt, u64 addr,
 	struct stage2_attr_data data = {
 		.attr_set	= attr_set & attr_mask,
 		.attr_clr	= attr_clr & attr_mask,
-		.mm_ops		= pgt->mm_ops,
 	};
 	struct kvm_pgtable_walker walker = {
 		.cb		= stage2_attr_walker,
@@ -1198,7 +1184,7 @@ int __kvm_pgtable_stage2_init(struct kvm_pgtable *pgt, struct kvm_s2_mmu *mmu,
 static int stage2_free_walker(const struct kvm_pgtable_visit_ctx *ctx,
 			      enum kvm_pgtable_walk_flags visit)
 {
-	struct kvm_pgtable_mm_ops *mm_ops = ctx->arg;
+	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
 
 	if (!stage2_pte_is_counted(ctx->old))
 		return 0;
@@ -1218,7 +1204,6 @@ void kvm_pgtable_stage2_destroy(struct kvm_pgtable *pgt)
 		.cb	= stage2_free_walker,
 		.flags	= KVM_PGTABLE_WALK_LEAF |
 			  KVM_PGTABLE_WALK_TABLE_POST,
-		.arg	= pgt->mm_ops,
 	};
 
 	WARN_ON(kvm_pgtable_walk(pgt, 0, BIT(pgt->ia_bits), &walker));
-- 
2.38.1.273.g43a17bfeac-goog


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[PATCH v3 04/15] KVM: arm64: Don't pass kvm_pgtable through kvm_pgtable_walk_data

[Oliver Upton]

In order to tear down page tables from outside the context of
kvm_pgtable (such as an RCU callback), stop passing a pointer through
kvm_pgtable_walk_data.

No functional change intended.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/kvm/hyp/pgtable.c | 18 +++++-------------
 1 file changed, 5 insertions(+), 13 deletions(-)

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index db25e81a9890..93989b750a26 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -50,7 +50,6 @@
 #define KVM_MAX_OWNER_ID		1
 
 struct kvm_pgtable_walk_data {
-	struct kvm_pgtable		*pgt;
 	struct kvm_pgtable_walker	*walker;
 
 	u64				addr;
@@ -88,7 +87,7 @@ static u32 kvm_pgtable_idx(struct kvm_pgtable_walk_data *data, u32 level)
 	return (data->addr >> shift) & mask;
 }
 
-static u32 __kvm_pgd_page_idx(struct kvm_pgtable *pgt, u64 addr)
+static u32 kvm_pgd_page_idx(struct kvm_pgtable *pgt, u64 addr)
 {
 	u64 shift = kvm_granule_shift(pgt->start_level - 1); /* May underflow */
 	u64 mask = BIT(pgt->ia_bits) - 1;
@@ -96,11 +95,6 @@ static u32 __kvm_pgd_page_idx(struct kvm_pgtable *pgt, u64 addr)
 	return (addr & mask) >> shift;
 }
 
-static u32 kvm_pgd_page_idx(struct kvm_pgtable_walk_data *data)
-{
-	return __kvm_pgd_page_idx(data->pgt, data->addr);
-}
-
 static u32 kvm_pgd_pages(u32 ia_bits, u32 start_level)
 {
 	struct kvm_pgtable pgt = {
@@ -108,7 +102,7 @@ static u32 kvm_pgd_pages(u32 ia_bits, u32 start_level)
 		.start_level	= start_level,
 	};
 
-	return __kvm_pgd_page_idx(&pgt, -1ULL) + 1;
+	return kvm_pgd_page_idx(&pgt, -1ULL) + 1;
 }
 
 static bool kvm_pte_table(kvm_pte_t pte, u32 level)
@@ -255,11 +249,10 @@ static int __kvm_pgtable_walk(struct kvm_pgtable_walk_data *data,
 	return ret;
 }
 
-static int _kvm_pgtable_walk(struct kvm_pgtable_walk_data *data)
+static int _kvm_pgtable_walk(struct kvm_pgtable *pgt, struct kvm_pgtable_walk_data *data)
 {
 	u32 idx;
 	int ret = 0;
-	struct kvm_pgtable *pgt = data->pgt;
 	u64 limit = BIT(pgt->ia_bits);
 
 	if (data->addr > limit || data->end > limit)
@@ -268,7 +261,7 @@ static int _kvm_pgtable_walk(struct kvm_pgtable_walk_data *data)
 	if (!pgt->pgd)
 		return -EINVAL;
 
-	for (idx = kvm_pgd_page_idx(data); data->addr < data->end; ++idx) {
+	for (idx = kvm_pgd_page_idx(pgt, data->addr); data->addr < data->end; ++idx) {
 		kvm_pte_t *ptep = &pgt->pgd[idx * PTRS_PER_PTE];
 
 		ret = __kvm_pgtable_walk(data, pgt->mm_ops, ptep, pgt->start_level);
@@ -283,13 +276,12 @@ int kvm_pgtable_walk(struct kvm_pgtable *pgt, u64 addr, u64 size,
 		     struct kvm_pgtable_walker *walker)
 {
 	struct kvm_pgtable_walk_data walk_data = {
-		.pgt	= pgt,
 		.addr	= ALIGN_DOWN(addr, PAGE_SIZE),
 		.end	= PAGE_ALIGN(walk_data.addr + size),
 		.walker	= walker,
 	};
 
-	return _kvm_pgtable_walk(&walk_data);
+	return _kvm_pgtable_walk(pgt, &walk_data);
 }
 
 struct leaf_walk_data {
-- 
2.38.1.273.g43a17bfeac-goog


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[PATCH v3 05/15] KVM: arm64: Add a helper to tear down unlinked stage-2 subtrees

[Oliver Upton]

A subsequent change to KVM will move the tear down of an unlinked
stage-2 subtree out of the critical path of the break-before-make
sequence.

Introduce a new helper for tearing down unlinked stage-2 subtrees.
Leverage the existing stage-2 free walkers to do so, with a deep call
into __kvm_pgtable_walk() as the subtree is no longer reachable from the
root.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/include/asm/kvm_pgtable.h | 11 +++++++++++
 arch/arm64/kvm/hyp/pgtable.c         | 23 +++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index a752793482cb..93b1feeaebab 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -333,6 +333,17 @@ int __kvm_pgtable_stage2_init(struct kvm_pgtable *pgt, struct kvm_s2_mmu *mmu,
  */
 void kvm_pgtable_stage2_destroy(struct kvm_pgtable *pgt);
 
+/**
+ * kvm_pgtable_stage2_free_removed() - Free a removed stage-2 paging structure.
+ * @mm_ops:	Memory management callbacks.
+ * @pgtable:	Unlinked stage-2 paging structure to be freed.
+ * @level:	Level of the stage-2 paging structure to be freed.
+ *
+ * The page-table is assumed to be unreachable by any hardware walkers prior to
+ * freeing and therefore no TLB invalidation is performed.
+ */
+void kvm_pgtable_stage2_free_removed(struct kvm_pgtable_mm_ops *mm_ops, void *pgtable, u32 level);
+
 /**
  * kvm_pgtable_stage2_map() - Install a mapping in a guest stage-2 page-table.
  * @pgt:	Page-table structure initialised by kvm_pgtable_stage2_init*().
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 93989b750a26..363a5cce7e1a 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -1203,3 +1203,26 @@ void kvm_pgtable_stage2_destroy(struct kvm_pgtable *pgt)
 	pgt->mm_ops->free_pages_exact(pgt->pgd, pgd_sz);
 	pgt->pgd = NULL;
 }
+
+void kvm_pgtable_stage2_free_removed(struct kvm_pgtable_mm_ops *mm_ops, void *pgtable, u32 level)
+{
+	kvm_pte_t *ptep = (kvm_pte_t *)pgtable;
+	struct kvm_pgtable_walker walker = {
+		.cb	= stage2_free_walker,
+		.flags	= KVM_PGTABLE_WALK_LEAF |
+			  KVM_PGTABLE_WALK_TABLE_POST,
+	};
+	struct kvm_pgtable_walk_data data = {
+		.walker	= &walker,
+
+		/*
+		 * At this point the IPA really doesn't matter, as the page
+		 * table being traversed has already been removed from the stage
+		 * 2. Set an appropriate range to cover the entire page table.
+		 */
+		.addr	= 0,
+		.end	= kvm_granule_size(level),
+	};
+
+	WARN_ON(__kvm_pgtable_walk(&data, mm_ops, ptep, level));
+}
-- 
2.38.1.273.g43a17bfeac-goog


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[PATCH v3 06/15] KVM: arm64: Tear down unlinked stage-2 subtree after break-before-make

[Oliver Upton]

The break-before-make sequence is a bit annoying as it opens a window
wherein memory is unmapped from the guest. KVM should replace the PTE
as quickly as possible and avoid unnecessary work in between.

Presently, the stage-2 map walker tears down a removed table before
installing a block mapping when coalescing a table into a block. As the
removed table is no longer visible to hardware walkers after the
DSB+TLBI, it is possible to move the remaining cleanup to happen after
installing the new PTE.

Reshuffle the stage-2 map walker to install the new block entry in
the pre-order callback. Unwire all of the teardown logic and replace
it with a call to kvm_pgtable_stage2_free_removed() after fixing
the PTE. The post-order visitor is now completely unnecessary, so drop
it. Finally, touch up the comments to better represent the now
simplified map walker.

Note that the call to tear down the unlinked stage-2 is indirected
as a subsequent change will use an RCU callback to trigger tear down.
RCU is not available to pKVM, so there is a need to use different
implementations on pKVM and non-pKVM VMs.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/include/asm/kvm_pgtable.h  |  3 +
 arch/arm64/kvm/hyp/nvhe/mem_protect.c |  6 ++
 arch/arm64/kvm/hyp/pgtable.c          | 81 +++++++--------------------
 arch/arm64/kvm/mmu.c                  |  8 +++
 4 files changed, 37 insertions(+), 61 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 93b1feeaebab..7a8af3b686e8 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -85,6 +85,8 @@ static inline bool kvm_level_supports_block_mapping(u32 level)
  *				allocation is physically contiguous.
  * @free_pages_exact:		Free an exact number of memory pages previously
  *				allocated by zalloc_pages_exact.
+ * @free_removed_table:		Free a removed paging structure by unlinking and
+ *				dropping references.
  * @get_page:			Increment the refcount on a page.
  * @put_page:			Decrement the refcount on a page. When the
  *				refcount reaches 0 the page is automatically
@@ -103,6 +105,7 @@ struct kvm_pgtable_mm_ops {
 	void*		(*zalloc_page)(void *arg);
 	void*		(*zalloc_pages_exact)(size_t size);
 	void		(*free_pages_exact)(void *addr, size_t size);
+	void		(*free_removed_table)(void *addr, u32 level);
 	void		(*get_page)(void *addr);
 	void		(*put_page)(void *addr);
 	int		(*page_count)(void *addr);
diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index d21d1b08a055..735769886b55 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -79,6 +79,11 @@ static void host_s2_put_page(void *addr)
 	hyp_put_page(&host_s2_pool, addr);
 }
 
+static void host_s2_free_removed_table(void *addr, u32 level)
+{
+	kvm_pgtable_stage2_free_removed(&host_kvm.mm_ops, addr, level);
+}
+
 static int prepare_s2_pool(void *pgt_pool_base)
 {
 	unsigned long nr_pages, pfn;
@@ -93,6 +98,7 @@ static int prepare_s2_pool(void *pgt_pool_base)
 	host_kvm.mm_ops = (struct kvm_pgtable_mm_ops) {
 		.zalloc_pages_exact = host_s2_zalloc_pages_exact,
 		.zalloc_page = host_s2_zalloc_page,
+		.free_removed_table = host_s2_free_removed_table,
 		.phys_to_virt = hyp_phys_to_virt,
 		.virt_to_phys = hyp_virt_to_phys,
 		.page_count = hyp_page_count,
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 363a5cce7e1a..167777b42890 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -749,13 +749,13 @@ static int stage2_map_walker_try_leaf(const struct kvm_pgtable_visit_ctx *ctx,
 static int stage2_map_walk_table_pre(const struct kvm_pgtable_visit_ctx *ctx,
 				     struct stage2_map_data *data)
 {
-	if (data->anchor)
-		return 0;
+	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
+	kvm_pte_t *childp = kvm_pte_follow(ctx->old, mm_ops);
+	int ret;
 
 	if (!stage2_leaf_mapping_allowed(ctx, data))
 		return 0;
 
-	data->childp = kvm_pte_follow(ctx->old, ctx->mm_ops);
 	kvm_clear_pte(ctx->ptep);
 
 	/*
@@ -764,8 +764,13 @@ static int stage2_map_walk_table_pre(const struct kvm_pgtable_visit_ctx *ctx,
 	 * individually.
 	 */
 	kvm_call_hyp(__kvm_tlb_flush_vmid, data->mmu);
-	data->anchor = ctx->ptep;
-	return 0;
+
+	ret = stage2_map_walker_try_leaf(ctx, data);
+
+	mm_ops->put_page(ctx->ptep);
+	mm_ops->free_removed_table(childp, ctx->level + 1);
+
+	return ret;
 }
 
 static int stage2_map_walk_leaf(const struct kvm_pgtable_visit_ctx *ctx,
@@ -775,13 +780,6 @@ static int stage2_map_walk_leaf(const struct kvm_pgtable_visit_ctx *ctx,
 	kvm_pte_t *childp;
 	int ret;
 
-	if (data->anchor) {
-		if (stage2_pte_is_counted(ctx->old))
-			mm_ops->put_page(ctx->ptep);
-
-		return 0;
-	}
-
 	ret = stage2_map_walker_try_leaf(ctx, data);
 	if (ret != -E2BIG)
 		return ret;
@@ -810,49 +808,14 @@ static int stage2_map_walk_leaf(const struct kvm_pgtable_visit_ctx *ctx,
 	return 0;
 }
 
-static int stage2_map_walk_table_post(const struct kvm_pgtable_visit_ctx *ctx,
-				      struct stage2_map_data *data)
-{
-	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
-	kvm_pte_t *childp;
-	int ret = 0;
-
-	if (!data->anchor)
-		return 0;
-
-	if (data->anchor == ctx->ptep) {
-		childp = data->childp;
-		data->anchor = NULL;
-		data->childp = NULL;
-		ret = stage2_map_walk_leaf(ctx, data);
-	} else {
-		childp = kvm_pte_follow(ctx->old, mm_ops);
-	}
-
-	mm_ops->put_page(childp);
-	mm_ops->put_page(ctx->ptep);
-
-	return ret;
-}
-
 /*
- * This is a little fiddly, as we use all three of the walk flags. The idea
- * is that the TABLE_PRE callback runs for table entries on the way down,
- * looking for table entries which we could conceivably replace with a
- * block entry for this mapping. If it finds one, then it sets the 'anchor'
- * field in 'struct stage2_map_data' to point at the table entry, before
- * clearing the entry to zero and descending into the now detached table.
- *
- * The behaviour of the LEAF callback then depends on whether or not the
- * anchor has been set. If not, then we're not using a block mapping higher
- * up the table and we perform the mapping at the existing leaves instead.
- * If, on the other hand, the anchor _is_ set, then we drop references to
- * all valid leaves so that the pages beneath the anchor can be freed.
+ * The TABLE_PRE callback runs for table entries on the way down, looking
+ * for table entries which we could conceivably replace with a block entry
+ * for this mapping. If it finds one it replaces the entry and calls
+ * kvm_pgtable_mm_ops::free_removed_table() to tear down the detached table.
  *
- * Finally, the TABLE_POST callback does nothing if the anchor has not
- * been set, but otherwise frees the page-table pages while walking back up
- * the page-table, installing the block entry when it revisits the anchor
- * pointer and clearing the anchor to NULL.
+ * Otherwise, the LEAF callback performs the mapping at the existing leaves
+ * instead.
  */
 static int stage2_map_walker(const struct kvm_pgtable_visit_ctx *ctx,
 			     enum kvm_pgtable_walk_flags visit)
@@ -864,11 +827,9 @@ static int stage2_map_walker(const struct kvm_pgtable_visit_ctx *ctx,
 		return stage2_map_walk_table_pre(ctx, data);
 	case KVM_PGTABLE_WALK_LEAF:
 		return stage2_map_walk_leaf(ctx, data);
-	case KVM_PGTABLE_WALK_TABLE_POST:
-		return stage2_map_walk_table_post(ctx, data);
+	default:
+		return -EINVAL;
 	}
-
-	return -EINVAL;
 }
 
 int kvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size,
@@ -885,8 +846,7 @@ int kvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size,
 	struct kvm_pgtable_walker walker = {
 		.cb		= stage2_map_walker,
 		.flags		= KVM_PGTABLE_WALK_TABLE_PRE |
-				  KVM_PGTABLE_WALK_LEAF |
-				  KVM_PGTABLE_WALK_TABLE_POST,
+				  KVM_PGTABLE_WALK_LEAF,
 		.arg		= &map_data,
 	};
 
@@ -916,8 +876,7 @@ int kvm_pgtable_stage2_set_owner(struct kvm_pgtable *pgt, u64 addr, u64 size,
 	struct kvm_pgtable_walker walker = {
 		.cb		= stage2_map_walker,
 		.flags		= KVM_PGTABLE_WALK_TABLE_PRE |
-				  KVM_PGTABLE_WALK_LEAF |
-				  KVM_PGTABLE_WALK_TABLE_POST,
+				  KVM_PGTABLE_WALK_LEAF,
 		.arg		= &map_data,
 	};
 
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 60ee3d9f01f8..175a0e9a04b6 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -128,6 +128,13 @@ static void kvm_s2_free_pages_exact(void *virt, size_t size)
 	free_pages_exact(virt, size);
 }
 
+static struct kvm_pgtable_mm_ops kvm_s2_mm_ops;
+
+static void stage2_free_removed_table(void *addr, u32 level)
+{
+	kvm_pgtable_stage2_free_removed(&kvm_s2_mm_ops, addr, level);
+}
+
 static void kvm_host_get_page(void *addr)
 {
 	get_page(virt_to_page(addr));
@@ -662,6 +669,7 @@ static struct kvm_pgtable_mm_ops kvm_s2_mm_ops = {
 	.zalloc_page		= stage2_memcache_zalloc_page,
 	.zalloc_pages_exact	= kvm_s2_zalloc_pages_exact,
 	.free_pages_exact	= kvm_s2_free_pages_exact,
+	.free_removed_table	= stage2_free_removed_table,
 	.get_page		= kvm_host_get_page,
 	.put_page		= kvm_s2_put_page,
 	.page_count		= kvm_host_page_count,
-- 
2.38.1.273.g43a17bfeac-goog


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[PATCH v3 07/15] KVM: arm64: Use an opaque type for pteps

[Oliver Upton]

Use an opaque type for pteps and require visitors explicitly dereference
the pointer before using. Protecting page table memory with RCU requires
that KVM dereferences RCU-annotated pointers before using. However, RCU
is not available for use in the nVHE hypervisor and the opaque type can
be conditionally annotated with RCU for the stage-2 MMU.

Call the type a 'pteref' to avoid a naming collision with raw pteps. No
functional change intended.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/include/asm/kvm_pgtable.h |  9 ++++++++-
 arch/arm64/kvm/hyp/pgtable.c         | 23 ++++++++++++-----------
 2 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 7a8af3b686e8..e70cf57b719e 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -37,6 +37,13 @@ static inline u64 kvm_get_parange(u64 mmfr0)
 
 typedef u64 kvm_pte_t;
 
+typedef kvm_pte_t *kvm_pteref_t;
+
+static inline kvm_pte_t *kvm_dereference_pteref(kvm_pteref_t pteref, bool shared)
+{
+	return pteref;
+}
+
 #define KVM_PTE_VALID			BIT(0)
 
 #define KVM_PTE_ADDR_MASK		GENMASK(47, PAGE_SHIFT)
@@ -178,7 +185,7 @@ typedef bool (*kvm_pgtable_force_pte_cb_t)(u64 addr, u64 end,
 struct kvm_pgtable {
 	u32					ia_bits;
 	u32					start_level;
-	kvm_pte_t				*pgd;
+	kvm_pteref_t				pgd;
 	struct kvm_pgtable_mm_ops		*mm_ops;
 
 	/* Stage-2 only */
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 167777b42890..c4d103889a62 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -175,13 +175,14 @@ static int kvm_pgtable_visitor_cb(struct kvm_pgtable_walk_data *data,
 }
 
 static int __kvm_pgtable_walk(struct kvm_pgtable_walk_data *data,
-			      struct kvm_pgtable_mm_ops *mm_ops, kvm_pte_t *pgtable, u32 level);
+			      struct kvm_pgtable_mm_ops *mm_ops, kvm_pteref_t pgtable, u32 level);
 
 static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
 				      struct kvm_pgtable_mm_ops *mm_ops,
-				      kvm_pte_t *ptep, u32 level)
+				      kvm_pteref_t pteref, u32 level)
 {
 	enum kvm_pgtable_walk_flags flags = data->walker->flags;
+	kvm_pte_t *ptep = kvm_dereference_pteref(pteref, false);
 	struct kvm_pgtable_visit_ctx ctx = {
 		.ptep	= ptep,
 		.old	= READ_ONCE(*ptep),
@@ -193,7 +194,7 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
 		.flags	= flags,
 	};
 	int ret = 0;
-	kvm_pte_t *childp;
+	kvm_pteref_t childp;
 	bool table = kvm_pte_table(ctx.old, level);
 
 	if (table && (ctx.flags & KVM_PGTABLE_WALK_TABLE_PRE))
@@ -214,7 +215,7 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
 		goto out;
 	}
 
-	childp = kvm_pte_follow(ctx.old, mm_ops);
+	childp = (kvm_pteref_t)kvm_pte_follow(ctx.old, mm_ops);
 	ret = __kvm_pgtable_walk(data, mm_ops, childp, level + 1);
 	if (ret)
 		goto out;
@@ -227,7 +228,7 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
 }
 
 static int __kvm_pgtable_walk(struct kvm_pgtable_walk_data *data,
-			      struct kvm_pgtable_mm_ops *mm_ops, kvm_pte_t *pgtable, u32 level)
+			      struct kvm_pgtable_mm_ops *mm_ops, kvm_pteref_t pgtable, u32 level)
 {
 	u32 idx;
 	int ret = 0;
@@ -236,12 +237,12 @@ static int __kvm_pgtable_walk(struct kvm_pgtable_walk_data *data,
 		return -EINVAL;
 
 	for (idx = kvm_pgtable_idx(data, level); idx < PTRS_PER_PTE; ++idx) {
-		kvm_pte_t *ptep = &pgtable[idx];
+		kvm_pteref_t pteref = &pgtable[idx];
 
 		if (data->addr >= data->end)
 			break;
 
-		ret = __kvm_pgtable_visit(data, mm_ops, ptep, level);
+		ret = __kvm_pgtable_visit(data, mm_ops, pteref, level);
 		if (ret)
 			break;
 	}
@@ -262,9 +263,9 @@ static int _kvm_pgtable_walk(struct kvm_pgtable *pgt, struct kvm_pgtable_walk_da
 		return -EINVAL;
 
 	for (idx = kvm_pgd_page_idx(pgt, data->addr); data->addr < data->end; ++idx) {
-		kvm_pte_t *ptep = &pgt->pgd[idx * PTRS_PER_PTE];
+		kvm_pteref_t pteref = &pgt->pgd[idx * PTRS_PER_PTE];
 
-		ret = __kvm_pgtable_walk(data, pgt->mm_ops, ptep, pgt->start_level);
+		ret = __kvm_pgtable_walk(data, pgt->mm_ops, pteref, pgt->start_level);
 		if (ret)
 			break;
 	}
@@ -507,7 +508,7 @@ int kvm_pgtable_hyp_init(struct kvm_pgtable *pgt, u32 va_bits,
 {
 	u64 levels = ARM64_HW_PGTABLE_LEVELS(va_bits);
 
-	pgt->pgd = (kvm_pte_t *)mm_ops->zalloc_page(NULL);
+	pgt->pgd = (kvm_pteref_t)mm_ops->zalloc_page(NULL);
 	if (!pgt->pgd)
 		return -ENOMEM;
 
@@ -1116,7 +1117,7 @@ int __kvm_pgtable_stage2_init(struct kvm_pgtable *pgt, struct kvm_s2_mmu *mmu,
 	u32 start_level = VTCR_EL2_TGRAN_SL0_BASE - sl0;
 
 	pgd_sz = kvm_pgd_pages(ia_bits, start_level) * PAGE_SIZE;
-	pgt->pgd = mm_ops->zalloc_pages_exact(pgd_sz);
+	pgt->pgd = (kvm_pteref_t)mm_ops->zalloc_pages_exact(pgd_sz);
 	if (!pgt->pgd)
 		return -ENOMEM;
 
-- 
2.38.1.273.g43a17bfeac-goog


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[PATCH v3 08/15] KVM: arm64: Protect stage-2 traversal with RCU

[Oliver Upton]

The use of RCU is necessary to safely change the stage-2 page tables in
parallel. Acquire and release the RCU read lock when traversing the page
tables.

Use the _raw() flavor of rcu_dereference when changes to the page tables
are otherwise protected from parallel software walkers (e.g. holding the
write lock).

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/include/asm/kvm_pgtable.h | 41 ++++++++++++++++++++++++++++
 arch/arm64/kvm/hyp/pgtable.c         | 10 ++++++-
 2 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index e70cf57b719e..d1859e8550df 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -37,6 +37,13 @@ static inline u64 kvm_get_parange(u64 mmfr0)
 
 typedef u64 kvm_pte_t;
 
+/*
+ * RCU cannot be used in a non-kernel context such as the hyp. As such, page
+ * table walkers used in hyp do not call into RCU and instead use other
+ * synchronization mechanisms (such as a spinlock).
+ */
+#if defined(__KVM_NVHE_HYPERVISOR__) || defined(__KVM_VHE_HYPERVISOR__)
+
 typedef kvm_pte_t *kvm_pteref_t;
 
 static inline kvm_pte_t *kvm_dereference_pteref(kvm_pteref_t pteref, bool shared)
@@ -44,6 +51,40 @@ static inline kvm_pte_t *kvm_dereference_pteref(kvm_pteref_t pteref, bool shared
 	return pteref;
 }
 
+static inline void kvm_pgtable_walk_begin(void) {}
+static inline void kvm_pgtable_walk_end(void) {}
+
+static inline bool kvm_pgtable_walk_lock_held(void)
+{
+	return true;
+}
+
+#else
+
+typedef kvm_pte_t __rcu *kvm_pteref_t;
+
+static inline kvm_pte_t *kvm_dereference_pteref(kvm_pteref_t pteref, bool shared)
+{
+	return rcu_dereference_check(pteref, shared);
+}
+
+static inline void kvm_pgtable_walk_begin(void)
+{
+	rcu_read_lock();
+}
+
+static inline void kvm_pgtable_walk_end(void)
+{
+	rcu_read_unlock();
+}
+
+static inline bool kvm_pgtable_walk_lock_held(void)
+{
+	return rcu_read_lock_held();
+}
+
+#endif
+
 #define KVM_PTE_VALID			BIT(0)
 
 #define KVM_PTE_ADDR_MASK		GENMASK(47, PAGE_SHIFT)
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index c4d103889a62..5bab932aeaec 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -171,6 +171,9 @@ static int kvm_pgtable_visitor_cb(struct kvm_pgtable_walk_data *data,
 				  enum kvm_pgtable_walk_flags visit)
 {
 	struct kvm_pgtable_walker *walker = data->walker;
+
+	/* Ensure the appropriate lock is held (e.g. RCU lock for stage-2 MMU) */
+	WARN_ON_ONCE(kvm_pgtable_walk_shared(ctx) && !kvm_pgtable_walk_lock_held());
 	return walker->cb(ctx, visit);
 }
 
@@ -281,8 +284,13 @@ int kvm_pgtable_walk(struct kvm_pgtable *pgt, u64 addr, u64 size,
 		.end	= PAGE_ALIGN(walk_data.addr + size),
 		.walker	= walker,
 	};
+	int r;
+
+	kvm_pgtable_walk_begin();
+	r = _kvm_pgtable_walk(pgt, &walk_data);
+	kvm_pgtable_walk_end();
 
-	return _kvm_pgtable_walk(pgt, &walk_data);
+	return r;
 }
 
 struct leaf_walk_data {
-- 
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[PATCH v3 09/15] KVM: arm64: Free removed stage-2 tables in RCU callback

[Oliver Upton]

There is no real urgency to free a stage-2 subtree that was pruned.
Nonetheless, KVM does the tear down in the stage-2 fault path while
holding the MMU lock.

Free removed stage-2 subtrees after an RCU grace period. To guarantee
all stage-2 table pages are freed before killing a VM, add an
rcu_barrier() to the flush path.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/include/asm/kvm_pgtable.h |  2 +-
 arch/arm64/kvm/mmu.c                 | 14 +++++++++++++-
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index d1859e8550df..f35e7d4d73f1 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -65,7 +65,7 @@ typedef kvm_pte_t __rcu *kvm_pteref_t;
 
 static inline kvm_pte_t *kvm_dereference_pteref(kvm_pteref_t pteref, bool shared)
 {
-	return rcu_dereference_check(pteref, shared);
+	return rcu_dereference_check(pteref, !shared);
 }
 
 static inline void kvm_pgtable_walk_begin(void)
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 175a0e9a04b6..a1a623c5b069 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -130,9 +130,21 @@ static void kvm_s2_free_pages_exact(void *virt, size_t size)
 
 static struct kvm_pgtable_mm_ops kvm_s2_mm_ops;
 
+static void stage2_free_removed_table_rcu_cb(struct rcu_head *head)
+{
+	struct page *page = container_of(head, struct page, rcu_head);
+	void *pgtable = page_to_virt(page);
+	u32 level = page_private(page);
+
+	kvm_pgtable_stage2_free_removed(&kvm_s2_mm_ops, pgtable, level);
+}
+
 static void stage2_free_removed_table(void *addr, u32 level)
 {
-	kvm_pgtable_stage2_free_removed(&kvm_s2_mm_ops, addr, level);
+	struct page *page = virt_to_page(addr);
+
+	set_page_private(page, (unsigned long)level);
+	call_rcu(&page->rcu_head, stage2_free_removed_table_rcu_cb);
 }
 
 static void kvm_host_get_page(void *addr)
-- 
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[PATCH v3 10/15] KVM: arm64: Atomically update stage 2 leaf attributes in parallel walks

[Oliver Upton]

The stage2 attr walker is already used for parallel walks. Since commit
f783ef1c0e82 ("KVM: arm64: Add fast path to handle permission relaxation
during dirty logging"), KVM acquires the read lock when
write-unprotecting a PTE. However, the walker only uses a simple store
to update the PTE. This is safe as the only possible race is with
hardware updates to the access flag, which is benign.

However, a subsequent change to KVM will allow more changes to the stage
2 page tables to be done in parallel. Prepare the stage 2 attribute
walker by performing atomic updates to the PTE when walking in parallel.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/include/asm/kvm_pgtable.h |  8 +++++++
 arch/arm64/kvm/hyp/pgtable.c         | 31 ++++++++++++++++++++--------
 2 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index f35e7d4d73f1..7634b6964779 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -243,11 +243,14 @@ struct kvm_pgtable {
  *					children.
  * @KVM_PGTABLE_WALK_TABLE_POST:	Visit table entries after their
  *					children.
+ * @KVM_PGTABLE_WALK_SHARED:		Indicates the page-tables may be shared
+ *					with other software walkers.
  */
 enum kvm_pgtable_walk_flags {
 	KVM_PGTABLE_WALK_LEAF			= BIT(0),
 	KVM_PGTABLE_WALK_TABLE_PRE		= BIT(1),
 	KVM_PGTABLE_WALK_TABLE_POST		= BIT(2),
+	KVM_PGTABLE_WALK_SHARED			= BIT(3),
 };
 
 struct kvm_pgtable_visit_ctx {
@@ -264,6 +267,11 @@ struct kvm_pgtable_visit_ctx {
 typedef int (*kvm_pgtable_visitor_fn_t)(const struct kvm_pgtable_visit_ctx *ctx,
 					enum kvm_pgtable_walk_flags visit);
 
+static inline bool kvm_pgtable_walk_shared(const struct kvm_pgtable_visit_ctx *ctx)
+{
+	return ctx->flags & KVM_PGTABLE_WALK_SHARED;
+}
+
 /**
  * struct kvm_pgtable_walker - Hook into a page-table walk.
  * @cb:		Callback function to invoke during the walk.
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 5bab932aeaec..7c0dd58544b0 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -185,7 +185,7 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
 				      kvm_pteref_t pteref, u32 level)
 {
 	enum kvm_pgtable_walk_flags flags = data->walker->flags;
-	kvm_pte_t *ptep = kvm_dereference_pteref(pteref, false);
+	kvm_pte_t *ptep = kvm_dereference_pteref(pteref, flags & KVM_PGTABLE_WALK_SHARED);
 	struct kvm_pgtable_visit_ctx ctx = {
 		.ptep	= ptep,
 		.old	= READ_ONCE(*ptep),
@@ -675,6 +675,16 @@ static bool stage2_pte_is_counted(kvm_pte_t pte)
 	return !!pte;
 }
 
+static bool stage2_try_set_pte(const struct kvm_pgtable_visit_ctx *ctx, kvm_pte_t new)
+{
+	if (!kvm_pgtable_walk_shared(ctx)) {
+		WRITE_ONCE(*ctx->ptep, new);
+		return true;
+	}
+
+	return cmpxchg(ctx->ptep, ctx->old, new) == ctx->old;
+}
+
 static void stage2_put_pte(const struct kvm_pgtable_visit_ctx *ctx, struct kvm_s2_mmu *mmu,
 			   struct kvm_pgtable_mm_ops *mm_ops)
 {
@@ -986,7 +996,9 @@ static int stage2_attr_walker(const struct kvm_pgtable_visit_ctx *ctx,
 		    stage2_pte_executable(pte) && !stage2_pte_executable(ctx->old))
 			mm_ops->icache_inval_pou(kvm_pte_follow(pte, mm_ops),
 						  kvm_granule_size(ctx->level));
-		WRITE_ONCE(*ctx->ptep, pte);
+
+		if (!stage2_try_set_pte(ctx, pte))
+			return -EAGAIN;
 	}
 
 	return 0;
@@ -995,7 +1007,7 @@ static int stage2_attr_walker(const struct kvm_pgtable_visit_ctx *ctx,
 static int stage2_update_leaf_attrs(struct kvm_pgtable *pgt, u64 addr,
 				    u64 size, kvm_pte_t attr_set,
 				    kvm_pte_t attr_clr, kvm_pte_t *orig_pte,
-				    u32 *level)
+				    u32 *level, enum kvm_pgtable_walk_flags flags)
 {
 	int ret;
 	kvm_pte_t attr_mask = KVM_PTE_LEAF_ATTR_LO | KVM_PTE_LEAF_ATTR_HI;
@@ -1006,7 +1018,7 @@ static int stage2_update_leaf_attrs(struct kvm_pgtable *pgt, u64 addr,
 	struct kvm_pgtable_walker walker = {
 		.cb		= stage2_attr_walker,
 		.arg		= &data,
-		.flags		= KVM_PGTABLE_WALK_LEAF,
+		.flags		= flags | KVM_PGTABLE_WALK_LEAF,
 	};
 
 	ret = kvm_pgtable_walk(pgt, addr, size, &walker);
@@ -1025,14 +1037,14 @@ int kvm_pgtable_stage2_wrprotect(struct kvm_pgtable *pgt, u64 addr, u64 size)
 {
 	return stage2_update_leaf_attrs(pgt, addr, size, 0,
 					KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W,
-					NULL, NULL);
+					NULL, NULL, 0);
 }
 
 kvm_pte_t kvm_pgtable_stage2_mkyoung(struct kvm_pgtable *pgt, u64 addr)
 {
 	kvm_pte_t pte = 0;
 	stage2_update_leaf_attrs(pgt, addr, 1, KVM_PTE_LEAF_ATTR_LO_S2_AF, 0,
-				 &pte, NULL);
+				 &pte, NULL, 0);
 	dsb(ishst);
 	return pte;
 }
@@ -1041,7 +1053,7 @@ kvm_pte_t kvm_pgtable_stage2_mkold(struct kvm_pgtable *pgt, u64 addr)
 {
 	kvm_pte_t pte = 0;
 	stage2_update_leaf_attrs(pgt, addr, 1, 0, KVM_PTE_LEAF_ATTR_LO_S2_AF,
-				 &pte, NULL);
+				 &pte, NULL, 0);
 	/*
 	 * "But where's the TLBI?!", you scream.
 	 * "Over in the core code", I sigh.
@@ -1054,7 +1066,7 @@ kvm_pte_t kvm_pgtable_stage2_mkold(struct kvm_pgtable *pgt, u64 addr)
 bool kvm_pgtable_stage2_is_young(struct kvm_pgtable *pgt, u64 addr)
 {
 	kvm_pte_t pte = 0;
-	stage2_update_leaf_attrs(pgt, addr, 1, 0, 0, &pte, NULL);
+	stage2_update_leaf_attrs(pgt, addr, 1, 0, 0, &pte, NULL, 0);
 	return pte & KVM_PTE_LEAF_ATTR_LO_S2_AF;
 }
 
@@ -1077,7 +1089,8 @@ int kvm_pgtable_stage2_relax_perms(struct kvm_pgtable *pgt, u64 addr,
 	if (prot & KVM_PGTABLE_PROT_X)
 		clr |= KVM_PTE_LEAF_ATTR_HI_S2_XN;
 
-	ret = stage2_update_leaf_attrs(pgt, addr, 1, set, clr, NULL, &level);
+	ret = stage2_update_leaf_attrs(pgt, addr, 1, set, clr, NULL, &level,
+				       KVM_PGTABLE_WALK_SHARED);
 	if (!ret)
 		kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, pgt->mmu, addr, level);
 	return ret;
-- 
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[PATCH v3 11/15] KVM: arm64: Split init and set for table PTE

[Oliver Upton]

Create a helper to initialize a table and directly call
smp_store_release() to install it (for now). Prepare for a subsequent
change that generalizes PTE writes with a helper.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/kvm/hyp/pgtable.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 7c0dd58544b0..4c579b3beabf 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -136,16 +136,13 @@ static void kvm_clear_pte(kvm_pte_t *ptep)
 	WRITE_ONCE(*ptep, 0);
 }
 
-static void kvm_set_table_pte(kvm_pte_t *ptep, kvm_pte_t *childp,
-			      struct kvm_pgtable_mm_ops *mm_ops)
+static kvm_pte_t kvm_init_table_pte(kvm_pte_t *childp, struct kvm_pgtable_mm_ops *mm_ops)
 {
-	kvm_pte_t old = *ptep, pte = kvm_phys_to_pte(mm_ops->virt_to_phys(childp));
+	kvm_pte_t pte = kvm_phys_to_pte(mm_ops->virt_to_phys(childp));
 
 	pte |= FIELD_PREP(KVM_PTE_TYPE, KVM_PTE_TYPE_TABLE);
 	pte |= KVM_PTE_VALID;
-
-	WARN_ON(kvm_pte_valid(old));
-	smp_store_release(ptep, pte);
+	return pte;
 }
 
 static kvm_pte_t kvm_init_valid_leaf_pte(u64 pa, kvm_pte_t attr, u32 level)
@@ -413,7 +410,7 @@ static bool hyp_map_walker_try_leaf(const struct kvm_pgtable_visit_ctx *ctx,
 static int hyp_map_walker(const struct kvm_pgtable_visit_ctx *ctx,
 			  enum kvm_pgtable_walk_flags visit)
 {
-	kvm_pte_t *childp;
+	kvm_pte_t *childp, new;
 	struct hyp_map_data *data = ctx->arg;
 	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
 
@@ -427,8 +424,10 @@ static int hyp_map_walker(const struct kvm_pgtable_visit_ctx *ctx,
 	if (!childp)
 		return -ENOMEM;
 
-	kvm_set_table_pte(ctx->ptep, childp, mm_ops);
+	new = kvm_init_table_pte(childp, mm_ops);
 	mm_ops->get_page(ctx->ptep);
+	smp_store_release(ctx->ptep, new);
+
 	return 0;
 }
 
@@ -821,8 +820,9 @@ static int stage2_map_walk_leaf(const struct kvm_pgtable_visit_ctx *ctx,
 	if (stage2_pte_is_counted(ctx->old))
 		stage2_put_pte(ctx, data->mmu, mm_ops);
 
-	kvm_set_table_pte(ctx->ptep, childp, mm_ops);
+	new = kvm_init_table_pte(childp, mm_ops);
 	mm_ops->get_page(ctx->ptep);
+	smp_store_release(ctx->ptep, new);
 
 	return 0;
 }
-- 
2.38.1.273.g43a17bfeac-goog


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[PATCH v3 12/15] KVM: arm64: Make block->table PTE changes parallel-aware

[Oliver Upton]

In order to service stage-2 faults in parallel, stage-2 table walkers
must take exclusive ownership of the PTE being worked on. An additional
requirement of the architecture is that software must perform a
'break-before-make' operation when changing the block size used for
mapping memory.

Roll these two concepts together into helpers for performing a
'break-before-make' sequence. Use a special PTE value to indicate a PTE
has been locked by a software walker. Additionally, use an atomic
compare-exchange to 'break' the PTE when the stage-2 page tables are
possibly shared with another software walker. Elide the DSB + TLBI if
the evicted PTE was invalid (and thus not subject to break-before-make).

All of the atomics do nothing for now, as the stage-2 walker isn't fully
ready to perform parallel walks.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/kvm/hyp/pgtable.c | 82 +++++++++++++++++++++++++++++++++---
 1 file changed, 76 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 4c579b3beabf..1df858c21b2e 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -49,6 +49,12 @@
 #define KVM_INVALID_PTE_OWNER_MASK	GENMASK(9, 2)
 #define KVM_MAX_OWNER_ID		1
 
+/*
+ * Used to indicate a pte for which a 'break-before-make' sequence is in
+ * progress.
+ */
+#define KVM_INVALID_PTE_LOCKED		BIT(10)
+
 struct kvm_pgtable_walk_data {
 	struct kvm_pgtable_walker	*walker;
 
@@ -674,6 +680,11 @@ static bool stage2_pte_is_counted(kvm_pte_t pte)
 	return !!pte;
 }
 
+static bool stage2_pte_is_locked(kvm_pte_t pte)
+{
+	return !kvm_pte_valid(pte) && (pte & KVM_INVALID_PTE_LOCKED);
+}
+
 static bool stage2_try_set_pte(const struct kvm_pgtable_visit_ctx *ctx, kvm_pte_t new)
 {
 	if (!kvm_pgtable_walk_shared(ctx)) {
@@ -684,6 +695,64 @@ static bool stage2_try_set_pte(const struct kvm_pgtable_visit_ctx *ctx, kvm_pte_
 	return cmpxchg(ctx->ptep, ctx->old, new) == ctx->old;
 }
 
+/**
+ * stage2_try_break_pte() - Invalidates a pte according to the
+ *			    'break-before-make' requirements of the
+ *			    architecture.
+ *
+ * @ctx: context of the visited pte.
+ * @data: stage-2 map data
+ *
+ * Returns: true if the pte was successfully broken.
+ *
+ * If the removed pte was valid, performs the necessary serialization and TLB
+ * invalidation for the old value. For counted ptes, drops the reference count
+ * on the containing table page.
+ */
+static bool stage2_try_break_pte(const struct kvm_pgtable_visit_ctx *ctx,
+				 struct stage2_map_data *data)
+{
+	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
+
+	if (stage2_pte_is_locked(ctx->old)) {
+		/*
+		 * Should never occur if this walker has exclusive access to the
+		 * page tables.
+		 */
+		WARN_ON(!kvm_pgtable_walk_shared(ctx));
+		return false;
+	}
+
+	if (!stage2_try_set_pte(ctx, KVM_INVALID_PTE_LOCKED))
+		return false;
+
+	/*
+	 * Perform the appropriate TLB invalidation based on the evicted pte
+	 * value (if any).
+	 */
+	if (kvm_pte_table(ctx->old, ctx->level))
+		kvm_call_hyp(__kvm_tlb_flush_vmid, data->mmu);
+	else if (kvm_pte_valid(ctx->old))
+		kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, data->mmu, ctx->addr, ctx->level);
+
+	if (stage2_pte_is_counted(ctx->old))
+		mm_ops->put_page(ctx->ptep);
+
+	return true;
+}
+
+static void stage2_make_pte(const struct kvm_pgtable_visit_ctx *ctx, kvm_pte_t new)
+{
+	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
+
+	WARN_ON(!stage2_pte_is_locked(*ctx->ptep));
+
+	if (stage2_pte_is_counted(new))
+		mm_ops->get_page(ctx->ptep);
+
+	smp_store_release(ctx->ptep, new);
+}
+
 static void stage2_put_pte(const struct kvm_pgtable_visit_ctx *ctx, struct kvm_s2_mmu *mmu,
 			   struct kvm_pgtable_mm_ops *mm_ops)
 {
@@ -795,7 +864,7 @@ static int stage2_map_walk_leaf(const struct kvm_pgtable_visit_ctx *ctx,
 				struct stage2_map_data *data)
 {
 	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
-	kvm_pte_t *childp;
+	kvm_pte_t *childp, new;
 	int ret;
 
 	ret = stage2_map_walker_try_leaf(ctx, data);
@@ -812,17 +881,18 @@ static int stage2_map_walk_leaf(const struct kvm_pgtable_visit_ctx *ctx,
 	if (!childp)
 		return -ENOMEM;
 
+	if (!stage2_try_break_pte(ctx, data)) {
+		mm_ops->put_page(childp);
+		return -EAGAIN;
+	}
+
 	/*
 	 * If we've run into an existing block mapping then replace it with
 	 * a table. Accesses beyond 'end' that fall within the new table
 	 * will be mapped lazily.
 	 */
-	if (stage2_pte_is_counted(ctx->old))
-		stage2_put_pte(ctx, data->mmu, mm_ops);
-
 	new = kvm_init_table_pte(childp, mm_ops);
-	mm_ops->get_page(ctx->ptep);
-	smp_store_release(ctx->ptep, new);
+	stage2_make_pte(ctx, new);
 
 	return 0;
 }
-- 
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[PATCH v3 13/15] KVM: arm64: Make leaf->leaf PTE changes parallel-aware

[Oliver Upton]

Convert stage2_map_walker_try_leaf() to use the new break-before-make
helpers, thereby making the handler parallel-aware. As before, avoid the
break-before-make if recreating the existing mapping. Additionally,
retry execution if another vCPU thread is modifying the same PTE.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/kvm/hyp/pgtable.c | 26 ++++++++++++--------------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 1df858c21b2e..581ba688c6f7 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -804,18 +804,17 @@ static int stage2_map_walker_try_leaf(const struct kvm_pgtable_visit_ctx *ctx,
 	else
 		new = kvm_init_invalid_leaf_owner(data->owner_id);
 
-	if (stage2_pte_is_counted(ctx->old)) {
-		/*
-		 * Skip updating the PTE if we are trying to recreate the exact
-		 * same mapping or only change the access permissions. Instead,
-		 * the vCPU will exit one more time from guest if still needed
-		 * and then go through the path of relaxing permissions.
-		 */
-		if (!stage2_pte_needs_update(ctx->old, new))
-			return -EAGAIN;
+	/*
+	 * Skip updating the PTE if we are trying to recreate the exact
+	 * same mapping or only change the access permissions. Instead,
+	 * the vCPU will exit one more time from guest if still needed
+	 * and then go through the path of relaxing permissions.
+	 */
+	if (!stage2_pte_needs_update(ctx->old, new))
+		return -EAGAIN;
 
-		stage2_put_pte(ctx, data->mmu, mm_ops);
-	}
+	if (!stage2_try_break_pte(ctx, data))
+		return -EAGAIN;
 
 	/* Perform CMOs before installation of the guest stage-2 PTE */
 	if (mm_ops->dcache_clean_inval_poc && stage2_pte_cacheable(pgt, new))
@@ -825,9 +824,8 @@ static int stage2_map_walker_try_leaf(const struct kvm_pgtable_visit_ctx *ctx,
 	if (mm_ops->icache_inval_pou && stage2_pte_executable(new))
 		mm_ops->icache_inval_pou(kvm_pte_follow(new, mm_ops), granule);
 
-	smp_store_release(ctx->ptep, new);
-	if (stage2_pte_is_counted(new))
-		mm_ops->get_page(ctx->ptep);
+	stage2_make_pte(ctx, new);
+
 	if (kvm_phys_is_valid(phys))
 		data->phys += granule;
 	return 0;
-- 
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[PATCH v3 14/15] KVM: arm64: Make table->block changes parallel-aware

[Oliver Upton]

stage2_map_walk_leaf() and friends now handle stage-2 PTEs generically,
and perform the correct flush when a table PTE is removed. Additionally,
they've been made parallel-aware, using an atomic break to take
ownership of the PTE.

Stop clearing the PTE in the pre-order callback and instead let
stage2_map_walk_leaf() deal with it.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/kvm/hyp/pgtable.c | 15 +++------------
 1 file changed, 3 insertions(+), 12 deletions(-)

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 581ba688c6f7..d08e14008bfb 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -841,21 +841,12 @@ static int stage2_map_walk_table_pre(const struct kvm_pgtable_visit_ctx *ctx,
 	if (!stage2_leaf_mapping_allowed(ctx, data))
 		return 0;
 
-	kvm_clear_pte(ctx->ptep);
-
-	/*
-	 * Invalidate the whole stage-2, as we may have numerous leaf
-	 * entries below us which would otherwise need invalidating
-	 * individually.
-	 */
-	kvm_call_hyp(__kvm_tlb_flush_vmid, data->mmu);
-
 	ret = stage2_map_walker_try_leaf(ctx, data);
+	if (ret)
+		return ret;
 
-	mm_ops->put_page(ctx->ptep);
 	mm_ops->free_removed_table(childp, ctx->level + 1);
-
-	return ret;
+	return 0;
 }
 
 static int stage2_map_walk_leaf(const struct kvm_pgtable_visit_ctx *ctx,
-- 
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[PATCH v3 15/15] KVM: arm64: Handle stage-2 faults in parallel

[Oliver Upton]

The stage-2 map walker has been made parallel-aware, and as such can be
called while only holding the read side of the MMU lock. Rip out the
conditional locking in user_mem_abort() and instead grab the read lock.
Continue to take the write lock from other callsites to
kvm_pgtable_stage2_map().

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/include/asm/kvm_pgtable.h  |  3 ++-
 arch/arm64/kvm/hyp/nvhe/mem_protect.c |  2 +-
 arch/arm64/kvm/hyp/pgtable.c          |  5 +++--
 arch/arm64/kvm/mmu.c                  | 31 ++++++---------------------
 4 files changed, 13 insertions(+), 28 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 7634b6964779..a874ce0ce7b5 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -412,6 +412,7 @@ void kvm_pgtable_stage2_free_removed(struct kvm_pgtable_mm_ops *mm_ops, void *pg
  * @prot:	Permissions and attributes for the mapping.
  * @mc:		Cache of pre-allocated and zeroed memory from which to allocate
  *		page-table pages.
+ * @flags:	Flags to control the page-table walk (ex. a shared walk)
  *
  * The offset of @addr within a page is ignored, @size is rounded-up to
  * the next page boundary and @phys is rounded-down to the previous page
@@ -433,7 +434,7 @@ void kvm_pgtable_stage2_free_removed(struct kvm_pgtable_mm_ops *mm_ops, void *pg
  */
 int kvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size,
 			   u64 phys, enum kvm_pgtable_prot prot,
-			   void *mc);
+			   void *mc, enum kvm_pgtable_walk_flags flags);
 
 /**
  * kvm_pgtable_stage2_set_owner() - Unmap and annotate pages in the IPA space to
diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index 735769886b55..f6d82bf33ce1 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -257,7 +257,7 @@ static inline int __host_stage2_idmap(u64 start, u64 end,
 				      enum kvm_pgtable_prot prot)
 {
 	return kvm_pgtable_stage2_map(&host_kvm.pgt, start, end - start, start,
-				      prot, &host_s2_pool);
+				      prot, &host_s2_pool, 0);
 }
 
 /*
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index d08e14008bfb..9ffe2e0bccb9 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -912,7 +912,7 @@ static int stage2_map_walker(const struct kvm_pgtable_visit_ctx *ctx,
 
 int kvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size,
 			   u64 phys, enum kvm_pgtable_prot prot,
-			   void *mc)
+			   void *mc, enum kvm_pgtable_walk_flags flags)
 {
 	int ret;
 	struct stage2_map_data map_data = {
@@ -923,7 +923,8 @@ int kvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size,
 	};
 	struct kvm_pgtable_walker walker = {
 		.cb		= stage2_map_walker,
-		.flags		= KVM_PGTABLE_WALK_TABLE_PRE |
+		.flags		= flags |
+				  KVM_PGTABLE_WALK_TABLE_PRE |
 				  KVM_PGTABLE_WALK_LEAF,
 		.arg		= &map_data,
 	};
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index a1a623c5b069..93f014a97abf 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -861,7 +861,7 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
 
 		write_lock(&kvm->mmu_lock);
 		ret = kvm_pgtable_stage2_map(pgt, addr, PAGE_SIZE, pa, prot,
-					     &cache);
+					     &cache, 0);
 		write_unlock(&kvm->mmu_lock);
 		if (ret)
 			break;
@@ -1156,7 +1156,6 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	gfn_t gfn;
 	kvm_pfn_t pfn;
 	bool logging_active = memslot_is_logging(memslot);
-	bool use_read_lock = false;
 	unsigned long fault_level = kvm_vcpu_trap_get_fault_level(vcpu);
 	unsigned long vma_pagesize, fault_granule;
 	enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_R;
@@ -1191,8 +1190,6 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	if (logging_active) {
 		force_pte = true;
 		vma_shift = PAGE_SHIFT;
-		use_read_lock = (fault_status == FSC_PERM && write_fault &&
-				 fault_granule == PAGE_SIZE);
 	} else {
 		vma_shift = get_vma_page_shift(vma, hva);
 	}
@@ -1291,15 +1288,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	if (exec_fault && device)
 		return -ENOEXEC;
 
-	/*
-	 * To reduce MMU contentions and enhance concurrency during dirty
-	 * logging dirty logging, only acquire read lock for permission
-	 * relaxation.
-	 */
-	if (use_read_lock)
-		read_lock(&kvm->mmu_lock);
-	else
-		write_lock(&kvm->mmu_lock);
+	read_lock(&kvm->mmu_lock);
 	pgt = vcpu->arch.hw_mmu->pgt;
 	if (mmu_invalidate_retry(kvm, mmu_seq))
 		goto out_unlock;
@@ -1343,15 +1332,12 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	 * permissions only if vma_pagesize equals fault_granule. Otherwise,
 	 * kvm_pgtable_stage2_map() should be called to change block size.
 	 */
-	if (fault_status == FSC_PERM && vma_pagesize == fault_granule) {
+	if (fault_status == FSC_PERM && vma_pagesize == fault_granule)
 		ret = kvm_pgtable_stage2_relax_perms(pgt, fault_ipa, prot);
-	} else {
-		WARN_ONCE(use_read_lock, "Attempted stage-2 map outside of write lock\n");
-
+	else
 		ret = kvm_pgtable_stage2_map(pgt, fault_ipa, vma_pagesize,
 					     __pfn_to_phys(pfn), prot,
-					     memcache);
-	}
+					     memcache, KVM_PGTABLE_WALK_SHARED);
 
 	/* Mark the page dirty only if the fault is handled successfully */
 	if (writable && !ret) {
@@ -1360,10 +1346,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	}
 
 out_unlock:
-	if (use_read_lock)
-		read_unlock(&kvm->mmu_lock);
-	else
-		write_unlock(&kvm->mmu_lock);
+	read_unlock(&kvm->mmu_lock);
 	kvm_set_pfn_accessed(pfn);
 	kvm_release_pfn_clean(pfn);
 	return ret != -EAGAIN ? ret : 0;
@@ -1569,7 +1552,7 @@ bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 	 */
 	kvm_pgtable_stage2_map(kvm->arch.mmu.pgt, range->start << PAGE_SHIFT,
 			       PAGE_SIZE, __pfn_to_phys(pfn),
-			       KVM_PGTABLE_PROT_R, NULL);
+			       KVM_PGTABLE_PROT_R, NULL, 0);
 
 	return false;
 }
-- 
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Re: [PATCH v3 00/15] KVM: arm64: Parallel stage-2 fault handling

[Oliver Upton]

On Thu, Oct 27, 2022 at 10:17:37PM +0000, Oliver Upton wrote:
> Presently KVM only takes a read lock for stage 2 faults if it believes
> the fault can be fixed by relaxing permissions on a PTE (write unprotect
> for dirty logging). Otherwise, stage 2 faults grab the write lock, which
> predictably can pile up all the vCPUs in a sufficiently large VM.
> 
> Like the TDP MMU for x86, this series loosens the locking around
> manipulations of the stage 2 page tables to allow parallel faults. RCU
> and atomics are exploited to safely build/destroy the stage 2 page
> tables in light of multiple software observers.
> 
> Patches 1-4 clean up the context associated with a page table walk / PTE
> visit. This is helpful for:
>  - Extending the context passed through for a visit
>  - Building page table walkers that operate outside of a kvm_pgtable
>    context (e.g. RCU callback)

As is always the case, I failed to update the changelogs when twiddling
things around a bit more.

Specifically, 8/15 and 14/15 don't directly match the diffs anymore. I
wont respin (yet) to avoid bombarding mailboxes.

--
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Re: [PATCH v3 08/15] KVM: arm64: Protect stage-2 traversal with RCU

[Oliver Upton]

On Thu, Oct 27, 2022 at 10:17:45PM +0000, Oliver Upton wrote:
> The use of RCU is necessary to safely change the stage-2 page tables in
> parallel. Acquire and release the RCU read lock when traversing the page
> tables.
> 
> Use the _raw() flavor of rcu_dereference when changes to the page tables
> are otherwise protected from parallel software walkers (e.g. holding the
> write lock).
> 
> Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
> ---
>  arch/arm64/include/asm/kvm_pgtable.h | 41 ++++++++++++++++++++++++++++
>  arch/arm64/kvm/hyp/pgtable.c         | 10 ++++++-
>  2 files changed, 50 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> index e70cf57b719e..d1859e8550df 100644
> --- a/arch/arm64/include/asm/kvm_pgtable.h
> +++ b/arch/arm64/include/asm/kvm_pgtable.h
> @@ -37,6 +37,13 @@ static inline u64 kvm_get_parange(u64 mmfr0)
>  
>  typedef u64 kvm_pte_t;
>  
> +/*
> + * RCU cannot be used in a non-kernel context such as the hyp. As such, page
> + * table walkers used in hyp do not call into RCU and instead use other
> + * synchronization mechanisms (such as a spinlock).
> + */
> +#if defined(__KVM_NVHE_HYPERVISOR__) || defined(__KVM_VHE_HYPERVISOR__)
> +
>  typedef kvm_pte_t *kvm_pteref_t;
>  
>  static inline kvm_pte_t *kvm_dereference_pteref(kvm_pteref_t pteref, bool shared)
> @@ -44,6 +51,40 @@ static inline kvm_pte_t *kvm_dereference_pteref(kvm_pteref_t pteref, bool shared
>  	return pteref;
>  }
>  
> +static inline void kvm_pgtable_walk_begin(void) {}
> +static inline void kvm_pgtable_walk_end(void) {}
> +
> +static inline bool kvm_pgtable_walk_lock_held(void)
> +{
> +	return true;
> +}
> +
> +#else
> +
> +typedef kvm_pte_t __rcu *kvm_pteref_t;
> +
> +static inline kvm_pte_t *kvm_dereference_pteref(kvm_pteref_t pteref, bool shared)
> +{
> +	return rcu_dereference_check(pteref, shared);

I accidentally squashed the fix for !shared into 9/15, not this patch.
Fix ready for v4.

--
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Re: [PATCH v3 08/15] KVM: arm64: Protect stage-2 traversal with RCU

[Sean Christopherson]

On Thu, Oct 27, 2022, Oliver Upton wrote:
> The use of RCU is necessary to safely change the stage-2 page tables in
> parallel.

RCU isn't strictly necessary, it's simply _a_ way to ensure readers have gone
away prior to freeing memory.  E.g. another method (used on x86 at least), is to
disable IRQs when walking page tables without holding mmu_lock, and then requiring
paths that free page tables to effectively do an IPI shootdown of all CPUs that
are reading page tables.

And "safely change" is misleading.  RCU doesn't allow safely _changing_ page
tables; if RCU did, then patch 10 wouldn't need to implement atomic updates.
Protecting page table walks with RCU is purely about ensuring readers have gone
away prior to freeing the backing memory, an entirely different mechanism is needed
to allow parallel updates, e.g. the CMPXCHG + KVM_INVALID_PTE_LOCKED approach to
ensure only one walker "owns" the detached page table.

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Re: [PATCH v3 09/15] KVM: arm64: Free removed stage-2 tables in RCU callback

[Sean Christopherson]

On Thu, Oct 27, 2022, Oliver Upton wrote:
> There is no real urgency to free a stage-2 subtree that was pruned.
> Nonetheless, KVM does the tear down in the stage-2 fault path while
> holding the MMU lock.
> 
> Free removed stage-2 subtrees after an RCU grace period. To guarantee
> all stage-2 table pages are freed before killing a VM, add an
> rcu_barrier() to the flush path.

This is _very_ misleading.  The above paints RCU as an optimization of sorts to
avoid doing work while holding mmu_lock.  Freeing page tables in an RCU callback
is _required_ for correctness when allowing parallel page faults to remove page
tables, as holding mmu_lock for read in that case doesn't ensure no other CPU is
accessing and/or holds a reference to the to-be-freed page table.

IMO, this patch should to be squashed with the previous patch, "Protect stage-2
traversal with RCU".  One doesn't make any sense without the other.

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Re: [PATCH v3 09/15] KVM: arm64: Free removed stage-2 tables in RCU callback

[Oliver Upton]

On Tue, Nov 01, 2022 at 08:28:04PM +0000, Sean Christopherson wrote:
> On Thu, Oct 27, 2022, Oliver Upton wrote:
> > There is no real urgency to free a stage-2 subtree that was pruned.
> > Nonetheless, KVM does the tear down in the stage-2 fault path while
> > holding the MMU lock.
> > 

[ copy ]

> This is _very_ misleading.  The above paints RCU as an optimization of sorts to
> avoid doing work while holding mmu_lock.  Freeing page tables in an RCU callback
> is _required_ for correctness when allowing parallel page faults to remove page
> tables, as holding mmu_lock for read in that case doesn't ensure no other CPU is
> accessing and/or holds a reference to the to-be-freed page table.

Agree, but it is still important to reason about what is changing here
too. Moving work out of the vCPU fault path _is_ valuable, though
ancillary to the correctness requirements.

> IMO, this patch should to be squashed with the previous patch, "Protect stage-2
> traversal with RCU".  One doesn't make any sense without the other.

I had split these up back when this series was a lot more gnarly and
there was too much slop in a single diff. That isn't the case any more,
so yeah I'll squash them.

[ paste ]

> > Free removed stage-2 subtrees after an RCU grace period. To guarantee
> > all stage-2 table pages are freed before killing a VM, add an
> > rcu_barrier() to the flush path.

An aside, this is flat-out wrong now.

--
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Re: [PATCH v3 09/15] KVM: arm64: Free removed stage-2 tables in RCU callback

[Sean Christopherson]

On Tue, Nov 01, 2022, Oliver Upton wrote:
> On Tue, Nov 01, 2022 at 08:28:04PM +0000, Sean Christopherson wrote:
> > On Thu, Oct 27, 2022, Oliver Upton wrote:
> > > There is no real urgency to free a stage-2 subtree that was pruned.
> > > Nonetheless, KVM does the tear down in the stage-2 fault path while
> > > holding the MMU lock.
> > > 
> 
> [ copy ]
> 
> > This is _very_ misleading.  The above paints RCU as an optimization of sorts to
> > avoid doing work while holding mmu_lock.  Freeing page tables in an RCU callback
> > is _required_ for correctness when allowing parallel page faults to remove page
> > tables, as holding mmu_lock for read in that case doesn't ensure no other CPU is
> > accessing and/or holds a reference to the to-be-freed page table.
> 
> Agree, but it is still important to reason about what is changing here
> too. Moving work out of the vCPU fault path _is_ valuable, though
> ancillary to the correctness requirements.

Sure, but that's at best a footnote.  Similar to protecting freeing, RCU isn't
the only option for moving work out of the vCPU fault path.  In fact, it's probably
one of the worst options because RCU callbacks run with soft IRQs disabled, i.e.
doing _too_ much in a RCU callback is a real problem.  If RCU weren't being used
to protect readers, deferring freeing via a workqueue, kthread, etc... would work
just as well, if not better.

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Re: [PATCH v3 12/15] KVM: arm64: Make block->table PTE changes parallel-aware

[Ricardo Koller]

On Thu, Oct 27, 2022 at 10:22:47PM +0000, Oliver Upton wrote:
> In order to service stage-2 faults in parallel, stage-2 table walkers
> must take exclusive ownership of the PTE being worked on. An additional
> requirement of the architecture is that software must perform a
> 'break-before-make' operation when changing the block size used for
> mapping memory.
> 
> Roll these two concepts together into helpers for performing a
> 'break-before-make' sequence. Use a special PTE value to indicate a PTE
> has been locked by a software walker. Additionally, use an atomic
> compare-exchange to 'break' the PTE when the stage-2 page tables are
> possibly shared with another software walker. Elide the DSB + TLBI if
> the evicted PTE was invalid (and thus not subject to break-before-make).
> 
> All of the atomics do nothing for now, as the stage-2 walker isn't fully
> ready to perform parallel walks.
> 
> Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
> ---
>  arch/arm64/kvm/hyp/pgtable.c | 82 +++++++++++++++++++++++++++++++++---
>  1 file changed, 76 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index 4c579b3beabf..1df858c21b2e 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -49,6 +49,12 @@
>  #define KVM_INVALID_PTE_OWNER_MASK	GENMASK(9, 2)
>  #define KVM_MAX_OWNER_ID		1
>  
> +/*
> + * Used to indicate a pte for which a 'break-before-make' sequence is in
> + * progress.
> + */
> +#define KVM_INVALID_PTE_LOCKED		BIT(10)
> +
>  struct kvm_pgtable_walk_data {
>  	struct kvm_pgtable_walker	*walker;
>  
> @@ -674,6 +680,11 @@ static bool stage2_pte_is_counted(kvm_pte_t pte)
>  	return !!pte;
>  }
>  
> +static bool stage2_pte_is_locked(kvm_pte_t pte)
> +{
> +	return !kvm_pte_valid(pte) && (pte & KVM_INVALID_PTE_LOCKED);
> +}
> +
>  static bool stage2_try_set_pte(const struct kvm_pgtable_visit_ctx *ctx, kvm_pte_t new)
>  {
>  	if (!kvm_pgtable_walk_shared(ctx)) {
> @@ -684,6 +695,64 @@ static bool stage2_try_set_pte(const struct kvm_pgtable_visit_ctx *ctx, kvm_pte_
>  	return cmpxchg(ctx->ptep, ctx->old, new) == ctx->old;
>  }
>  
> +/**
> + * stage2_try_break_pte() - Invalidates a pte according to the
> + *			    'break-before-make' requirements of the
> + *			    architecture.
> + *
> + * @ctx: context of the visited pte.
> + * @data: stage-2 map data
> + *
> + * Returns: true if the pte was successfully broken.
> + *
> + * If the removed pte was valid, performs the necessary serialization and TLB
> + * invalidation for the old value. For counted ptes, drops the reference count
> + * on the containing table page.
> + */
> +static bool stage2_try_break_pte(const struct kvm_pgtable_visit_ctx *ctx,
> +				 struct stage2_map_data *data)

Would it be possible to pass "kvm_s2_mmu *mmu" directly (instead of
"stage2_map_data *data")? so this function can be reused by other
walkers.  Another option would be to stash "struct kvm_s2_mmu" in
"struct kvm_pgtable_visit_ctx".

> +{
> +	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
> +
> +	if (stage2_pte_is_locked(ctx->old)) {
> +		/*
> +		 * Should never occur if this walker has exclusive access to the
> +		 * page tables.
> +		 */
> +		WARN_ON(!kvm_pgtable_walk_shared(ctx));
> +		return false;
> +	}
> +
> +	if (!stage2_try_set_pte(ctx, KVM_INVALID_PTE_LOCKED))
> +		return false;
> +
> +	/*
> +	 * Perform the appropriate TLB invalidation based on the evicted pte
> +	 * value (if any).
> +	 */
> +	if (kvm_pte_table(ctx->old, ctx->level))
> +		kvm_call_hyp(__kvm_tlb_flush_vmid, data->mmu);
> +	else if (kvm_pte_valid(ctx->old))
> +		kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, data->mmu, ctx->addr, ctx->level);
> +
> +	if (stage2_pte_is_counted(ctx->old))
> +		mm_ops->put_page(ctx->ptep);
> +
> +	return true;
> +}
> +
> +static void stage2_make_pte(const struct kvm_pgtable_visit_ctx *ctx, kvm_pte_t new)
> +{
> +	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
> +
> +	WARN_ON(!stage2_pte_is_locked(*ctx->ptep));
> +
> +	if (stage2_pte_is_counted(new))
> +		mm_ops->get_page(ctx->ptep);
> +
> +	smp_store_release(ctx->ptep, new);
> +}
> +
>  static void stage2_put_pte(const struct kvm_pgtable_visit_ctx *ctx, struct kvm_s2_mmu *mmu,
>  			   struct kvm_pgtable_mm_ops *mm_ops)
>  {
> @@ -795,7 +864,7 @@ static int stage2_map_walk_leaf(const struct kvm_pgtable_visit_ctx *ctx,
>  				struct stage2_map_data *data)
>  {
>  	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
> -	kvm_pte_t *childp;
> +	kvm_pte_t *childp, new;
>  	int ret;
>  
>  	ret = stage2_map_walker_try_leaf(ctx, data);
> @@ -812,17 +881,18 @@ static int stage2_map_walk_leaf(const struct kvm_pgtable_visit_ctx *ctx,
>  	if (!childp)
>  		return -ENOMEM;
>  
> +	if (!stage2_try_break_pte(ctx, data)) {
> +		mm_ops->put_page(childp);
> +		return -EAGAIN;
> +	}
> +
>  	/*
>  	 * If we've run into an existing block mapping then replace it with
>  	 * a table. Accesses beyond 'end' that fall within the new table
>  	 * will be mapped lazily.
>  	 */
> -	if (stage2_pte_is_counted(ctx->old))
> -		stage2_put_pte(ctx, data->mmu, mm_ops);
> -
>  	new = kvm_init_table_pte(childp, mm_ops);
> -	mm_ops->get_page(ctx->ptep);
> -	smp_store_release(ctx->ptep, new);
> +	stage2_make_pte(ctx, new);
>  
>  	return 0;
>  }
> -- 
> 2.38.1.273.g43a17bfeac-goog
> 

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Re: [PATCH v3 12/15] KVM: arm64: Make block->table PTE changes parallel-aware

[Oliver Upton]

On Tue, Nov 01, 2022 at 07:22:49PM -0700, Ricardo Koller wrote:
> On Thu, Oct 27, 2022 at 10:22:47PM +0000, Oliver Upton wrote:
> > In order to service stage-2 faults in parallel, stage-2 table walkers
> > must take exclusive ownership of the PTE being worked on. An additional
> > requirement of the architecture is that software must perform a
> > 'break-before-make' operation when changing the block size used for
> > mapping memory.
> > 
> > Roll these two concepts together into helpers for performing a
> > 'break-before-make' sequence. Use a special PTE value to indicate a PTE
> > has been locked by a software walker. Additionally, use an atomic
> > compare-exchange to 'break' the PTE when the stage-2 page tables are
> > possibly shared with another software walker. Elide the DSB + TLBI if
> > the evicted PTE was invalid (and thus not subject to break-before-make).
> > 
> > All of the atomics do nothing for now, as the stage-2 walker isn't fully
> > ready to perform parallel walks.
> > 
> > Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
> > ---
> >  arch/arm64/kvm/hyp/pgtable.c | 82 +++++++++++++++++++++++++++++++++---
> >  1 file changed, 76 insertions(+), 6 deletions(-)
> > 
> > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> > index 4c579b3beabf..1df858c21b2e 100644
> > --- a/arch/arm64/kvm/hyp/pgtable.c
> > +++ b/arch/arm64/kvm/hyp/pgtable.c
> > @@ -49,6 +49,12 @@
> >  #define KVM_INVALID_PTE_OWNER_MASK	GENMASK(9, 2)
> >  #define KVM_MAX_OWNER_ID		1
> >  
> > +/*
> > + * Used to indicate a pte for which a 'break-before-make' sequence is in
> > + * progress.
> > + */
> > +#define KVM_INVALID_PTE_LOCKED		BIT(10)
> > +
> >  struct kvm_pgtable_walk_data {
> >  	struct kvm_pgtable_walker	*walker;
> >  
> > @@ -674,6 +680,11 @@ static bool stage2_pte_is_counted(kvm_pte_t pte)
> >  	return !!pte;
> >  }
> >  
> > +static bool stage2_pte_is_locked(kvm_pte_t pte)
> > +{
> > +	return !kvm_pte_valid(pte) && (pte & KVM_INVALID_PTE_LOCKED);
> > +}
> > +
> >  static bool stage2_try_set_pte(const struct kvm_pgtable_visit_ctx *ctx, kvm_pte_t new)
> >  {
> >  	if (!kvm_pgtable_walk_shared(ctx)) {
> > @@ -684,6 +695,64 @@ static bool stage2_try_set_pte(const struct kvm_pgtable_visit_ctx *ctx, kvm_pte_
> >  	return cmpxchg(ctx->ptep, ctx->old, new) == ctx->old;
> >  }
> >  
> > +/**
> > + * stage2_try_break_pte() - Invalidates a pte according to the
> > + *			    'break-before-make' requirements of the
> > + *			    architecture.
> > + *
> > + * @ctx: context of the visited pte.
> > + * @data: stage-2 map data
> > + *
> > + * Returns: true if the pte was successfully broken.
> > + *
> > + * If the removed pte was valid, performs the necessary serialization and TLB
> > + * invalidation for the old value. For counted ptes, drops the reference count
> > + * on the containing table page.
> > + */
> > +static bool stage2_try_break_pte(const struct kvm_pgtable_visit_ctx *ctx,
> > +				 struct stage2_map_data *data)
> 
> Would it be possible to pass "kvm_s2_mmu *mmu" directly (instead of
> "stage2_map_data *data")? so this function can be reused by other
> walkers.

Sure, and I presume the ask is coming because you're layering eager page
splitting on top of this right? :-)

> Another option would be to stash "struct kvm_s2_mmu" in
> "struct kvm_pgtable_visit_ctx".

I don't think we'd want to do that. kvm_pgtable_visit_ctx is shared
amongst all walkers, including the hypervisor stage-1.

--
Thanks,
Oliver

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