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Subject[PATCH RFC 11/14] arm64: Move the ASID allocator code in a separate file
Date
We will want to re-use the ASID allocator in a separate context (e.g
allocating VMID). So move the code in a new file.

The function asid_check_context has been moved in the header as a static
inline function because we want to avoid add a branch when checking if the
ASID is still valid.

Signed-off-by: Julien Grall <julien.grall@arm.com>

---

This code will be used in the virt code for allocating VMID. I am not
entirely sure where to place it. Lib could potentially be a good place but I
am not entirely convinced the algo as it is could be used by other
architecture.

Looking at x86, it seems that it will not be possible to re-use because
the number of PCID (aka ASID) could be smaller than the number of CPUs.
See commit message 10af6235e0d327d42e1bad974385197817923dc1 "x86/mm:
Implement PCID based optimization: try to preserve old TLB entries using
PCI".
---
arch/arm64/include/asm/asid.h | 77 ++++++++++++++
arch/arm64/lib/Makefile | 2 +
arch/arm64/lib/asid.c | 185 +++++++++++++++++++++++++++++++++
arch/arm64/mm/context.c | 235 +-----------------------------------------
4 files changed, 267 insertions(+), 232 deletions(-)
create mode 100644 arch/arm64/include/asm/asid.h
create mode 100644 arch/arm64/lib/asid.c

diff --git a/arch/arm64/include/asm/asid.h b/arch/arm64/include/asm/asid.h
new file mode 100644
index 000000000000..bb62b587f37f
--- /dev/null
+++ b/arch/arm64/include/asm/asid.h
@@ -0,0 +1,77 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_ASM_ASID_H
+#define __ASM_ASM_ASID_H
+
+#include <linux/atomic.h>
+#include <linux/compiler.h>
+#include <linux/cpumask.h>
+#include <linux/percpu.h>
+#include <linux/spinlock.h>
+
+struct asid_info
+{
+ atomic64_t generation;
+ unsigned long *map;
+ atomic64_t __percpu *active;
+ u64 __percpu *reserved;
+ u32 bits;
+ /* Lock protecting the structure */
+ raw_spinlock_t lock;
+ /* Which CPU requires context flush on next call */
+ cpumask_t flush_pending;
+ /* Number of ASID allocated by context (shift value) */
+ unsigned int ctxt_shift;
+ /* Callback to locally flush the context. */
+ void (*flush_cpu_ctxt_cb)(void);
+};
+
+#define NUM_ASIDS(info) (1UL << ((info)->bits))
+#define NUM_CTXT_ASIDS(info) (NUM_ASIDS(info) >> (info)->ctxt_shift)
+
+#define active_asid(info, cpu) *per_cpu_ptr((info)->active, cpu)
+
+void asid_new_context(struct asid_info *info, atomic64_t *pasid,
+ unsigned int cpu);
+
+/*
+ * Check the ASID is still valid for the context. If not generate a new ASID.
+ *
+ * @pasid: Pointer to the current ASID batch
+ * @cpu: current CPU ID. Must have been acquired throught get_cpu()
+ */
+static inline void asid_check_context(struct asid_info *info,
+ atomic64_t *pasid, unsigned int cpu)
+{
+ u64 asid, old_active_asid;
+
+ asid = atomic64_read(pasid);
+
+ /*
+ * The memory ordering here is subtle.
+ * If our active_asid is non-zero and the ASID matches the current
+ * generation, then we update the active_asid entry with a relaxed
+ * cmpxchg. Racing with a concurrent rollover means that either:
+ *
+ * - We get a zero back from the cmpxchg and end up waiting on the
+ * lock. Taking the lock synchronises with the rollover and so
+ * we are forced to see the updated generation.
+ *
+ * - We get a valid ASID back from the cmpxchg, which means the
+ * relaxed xchg in flush_context will treat us as reserved
+ * because atomic RmWs are totally ordered for a given location.
+ */
+ old_active_asid = atomic64_read(&active_asid(info, cpu));
+ if (old_active_asid &&
+ !((asid ^ atomic64_read(&info->generation)) >> info->bits) &&
+ atomic64_cmpxchg_relaxed(&active_asid(info, cpu),
+ old_active_asid, asid))
+ return;
+
+ asid_new_context(info, pasid, cpu);
+}
+
+int asid_allocator_init(struct asid_info *info,
+ u32 bits, unsigned int asid_per_ctxt,
+ void (*flush_cpu_ctxt_cb)(void));
+
+#endif
diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile
index 5540a1638baf..720df5ee2aa2 100644
--- a/arch/arm64/lib/Makefile
+++ b/arch/arm64/lib/Makefile
@@ -5,6 +5,8 @@ lib-y := clear_user.o delay.o copy_from_user.o \
memcmp.o strcmp.o strncmp.o strlen.o strnlen.o \
strchr.o strrchr.o tishift.o

+lib-y += asid.o
+
ifeq ($(CONFIG_KERNEL_MODE_NEON), y)
obj-$(CONFIG_XOR_BLOCKS) += xor-neon.o
CFLAGS_REMOVE_xor-neon.o += -mgeneral-regs-only
diff --git a/arch/arm64/lib/asid.c b/arch/arm64/lib/asid.c
new file mode 100644
index 000000000000..72b71bfb32be
--- /dev/null
+++ b/arch/arm64/lib/asid.c
@@ -0,0 +1,185 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Generic ASID allocator.
+ *
+ * Based on arch/arm/mm/context.c
+ *
+ * Copyright (C) 2002-2003 Deep Blue Solutions Ltd, all rights reserved.
+ * Copyright (C) 2012 ARM Ltd.
+ */
+
+#include <linux/slab.h>
+
+#include <asm/asid.h>
+
+#define reserved_asid(info, cpu) *per_cpu_ptr((info)->reserved, cpu)
+
+#define ASID_MASK(info) (~GENMASK((info)->bits - 1, 0))
+#define ASID_FIRST_VERSION(info) (1UL << ((info)->bits))
+
+#define asid2idx(info, asid) (((asid) & ~ASID_MASK(info)) >> (info)->ctxt_shift)
+#define idx2asid(info, idx) (((idx) << (info)->ctxt_shift) & ~ASID_MASK(info))
+
+static void flush_context(struct asid_info *info)
+{
+ int i;
+ u64 asid;
+
+ /* Update the list of reserved ASIDs and the ASID bitmap. */
+ bitmap_clear(info->map, 0, NUM_CTXT_ASIDS(info));
+
+ for_each_possible_cpu(i) {
+ asid = atomic64_xchg_relaxed(&active_asid(info, i), 0);
+ /*
+ * If this CPU has already been through a
+ * rollover, but hasn't run another task in
+ * the meantime, we must preserve its reserved
+ * ASID, as this is the only trace we have of
+ * the process it is still running.
+ */
+ if (asid == 0)
+ asid = reserved_asid(info, i);
+ __set_bit(asid2idx(info, asid), info->map);
+ reserved_asid(info, i) = asid;
+ }
+
+ /*
+ * Queue a TLB invalidation for each CPU to perform on next
+ * context-switch
+ */
+ cpumask_setall(&info->flush_pending);
+}
+
+static bool check_update_reserved_asid(struct asid_info *info, u64 asid,
+ u64 newasid)
+{
+ int cpu;
+ bool hit = false;
+
+ /*
+ * Iterate over the set of reserved ASIDs looking for a match.
+ * If we find one, then we can update our mm to use newasid
+ * (i.e. the same ASID in the current generation) but we can't
+ * exit the loop early, since we need to ensure that all copies
+ * of the old ASID are updated to reflect the mm. Failure to do
+ * so could result in us missing the reserved ASID in a future
+ * generation.
+ */
+ for_each_possible_cpu(cpu) {
+ if (reserved_asid(info, cpu) == asid) {
+ hit = true;
+ reserved_asid(info, cpu) = newasid;
+ }
+ }
+
+ return hit;
+}
+
+static u64 new_context(struct asid_info *info, atomic64_t *pasid)
+{
+ static u32 cur_idx = 1;
+ u64 asid = atomic64_read(pasid);
+ u64 generation = atomic64_read(&info->generation);
+
+ if (asid != 0) {
+ u64 newasid = generation | (asid & ~ASID_MASK(info));
+
+ /*
+ * If our current ASID was active during a rollover, we
+ * can continue to use it and this was just a false alarm.
+ */
+ if (check_update_reserved_asid(info, asid, newasid))
+ return newasid;
+
+ /*
+ * We had a valid ASID in a previous life, so try to re-use
+ * it if possible.
+ */
+ if (!__test_and_set_bit(asid2idx(info, asid), info->map))
+ return newasid;
+ }
+
+ /*
+ * Allocate a free ASID. If we can't find one, take a note of the
+ * currently active ASIDs and mark the TLBs as requiring flushes. We
+ * always count from ASID #2 (index 1), as we use ASID #0 when setting
+ * a reserved TTBR0 for the init_mm and we allocate ASIDs in even/odd
+ * pairs.
+ */
+ asid = find_next_zero_bit(info->map, NUM_CTXT_ASIDS(info), cur_idx);
+ if (asid != NUM_CTXT_ASIDS(info))
+ goto set_asid;
+
+ /* We're out of ASIDs, so increment the global generation count */
+ generation = atomic64_add_return_relaxed(ASID_FIRST_VERSION(info),
+ &info->generation);
+ flush_context(info);
+
+ /* We have more ASIDs than CPUs, so this will always succeed */
+ asid = find_next_zero_bit(info->map, NUM_CTXT_ASIDS(info), 1);
+
+set_asid:
+ __set_bit(asid, info->map);
+ cur_idx = asid;
+ return idx2asid(info, asid) | generation;
+}
+
+/*
+ * Generate a new ASID for the context.
+ *
+ * @pasid: Pointer to the current ASID batch allocated. It will be updated
+ * with the new ASID batch.
+ * @cpu: current CPU ID. Must have been acquired through get_cpu()
+ */
+void asid_new_context(struct asid_info *info, atomic64_t *pasid,
+ unsigned int cpu)
+{
+ unsigned long flags;
+ u64 asid;
+
+ raw_spin_lock_irqsave(&info->lock, flags);
+ /* Check that our ASID belongs to the current generation. */
+ asid = atomic64_read(pasid);
+ if ((asid ^ atomic64_read(&info->generation)) >> info->bits) {
+ asid = new_context(info, pasid);
+ atomic64_set(pasid, asid);
+ }
+
+ if (cpumask_test_and_clear_cpu(cpu, &info->flush_pending))
+ info->flush_cpu_ctxt_cb();
+
+ atomic64_set(&active_asid(info, cpu), asid);
+ raw_spin_unlock_irqrestore(&info->lock, flags);
+}
+
+/*
+ * Initialize the ASID allocator
+ *
+ * @info: Pointer to the asid allocator structure
+ * @bits: Number of ASIDs available
+ * @asid_per_ctxt: Number of ASIDs to allocate per-context. ASIDs are
+ * allocated contiguously for a given context. This value should be a power of
+ * 2.
+ */
+int asid_allocator_init(struct asid_info *info,
+ u32 bits, unsigned int asid_per_ctxt,
+ void (*flush_cpu_ctxt_cb)(void))
+{
+ info->bits = bits;
+ info->ctxt_shift = ilog2(asid_per_ctxt);
+ info->flush_cpu_ctxt_cb = flush_cpu_ctxt_cb;
+ /*
+ * Expect allocation after rollover to fail if we don't have at least
+ * one more ASID than CPUs. ASID #0 is always reserved.
+ */
+ WARN_ON(NUM_CTXT_ASIDS(info) - 1 <= num_possible_cpus());
+ atomic64_set(&info->generation, ASID_FIRST_VERSION(info));
+ info->map = kcalloc(BITS_TO_LONGS(NUM_CTXT_ASIDS(info)),
+ sizeof(*info->map), GFP_KERNEL);
+ if (!info->map)
+ return -ENOMEM;
+
+ raw_spin_lock_init(&info->lock);
+
+ return 0;
+}
diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c
index 678a57b77c91..95ee7711a2ef 100644
--- a/arch/arm64/mm/context.c
+++ b/arch/arm64/mm/context.c
@@ -22,47 +22,22 @@
#include <linux/slab.h>
#include <linux/mm.h>

+#include <asm/asid.h>
#include <asm/cpufeature.h>
#include <asm/mmu_context.h>
#include <asm/smp.h>
#include <asm/tlbflush.h>

-struct asid_info
-{
- atomic64_t generation;
- unsigned long *map;
- atomic64_t __percpu *active;
- u64 __percpu *reserved;
- u32 bits;
- raw_spinlock_t lock;
- /* Which CPU requires context flush on next call */
- cpumask_t flush_pending;
- /* Number of ASID allocated by context (shift value) */
- unsigned int ctxt_shift;
- /* Callback to locally flush the context. */
- void (*flush_cpu_ctxt_cb)(void);
-} asid_info;
-
-#define active_asid(info, cpu) *per_cpu_ptr((info)->active, cpu)
-#define reserved_asid(info, cpu) *per_cpu_ptr((info)->reserved, cpu)
-
static DEFINE_PER_CPU(atomic64_t, active_asids);
static DEFINE_PER_CPU(u64, reserved_asids);

-#define ASID_MASK(info) (~GENMASK((info)->bits - 1, 0))
-#define NUM_ASIDS(info) (1UL << ((info)->bits))
-
-#define ASID_FIRST_VERSION(info) NUM_ASIDS(info)
-
#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
#define ASID_PER_CONTEXT 2
#else
#define ASID_PER_CONTEXT 1
#endif

-#define NUM_CTXT_ASIDS(info) (NUM_ASIDS(info) >> (info)->ctxt_shift)
-#define asid2idx(info, asid) (((asid) & ~ASID_MASK(info)) >> (info)->ctxt_shift)
-#define idx2asid(info, idx) (((idx) << (info)->ctxt_shift) & ~ASID_MASK(info))
+struct asid_info asid_info;

/* Get the ASIDBits supported by the current CPU */
static u32 get_cpu_asid_bits(void)
@@ -102,178 +77,6 @@ void verify_cpu_asid_bits(void)
}
}

-static void flush_context(struct asid_info *info)
-{
- int i;
- u64 asid;
-
- /* Update the list of reserved ASIDs and the ASID bitmap. */
- bitmap_clear(info->map, 0, NUM_CTXT_ASIDS(info));
-
- for_each_possible_cpu(i) {
- asid = atomic64_xchg_relaxed(&active_asid(info, i), 0);
- /*
- * If this CPU has already been through a
- * rollover, but hasn't run another task in
- * the meantime, we must preserve its reserved
- * ASID, as this is the only trace we have of
- * the process it is still running.
- */
- if (asid == 0)
- asid = reserved_asid(info, i);
- __set_bit(asid2idx(info, asid), info->map);
- reserved_asid(info, i) = asid;
- }
-
- /*
- * Queue a TLB invalidation for each CPU to perform on next
- * context-switch
- */
- cpumask_setall(&info->flush_pending);
-}
-
-static bool check_update_reserved_asid(struct asid_info *info, u64 asid,
- u64 newasid)
-{
- int cpu;
- bool hit = false;
-
- /*
- * Iterate over the set of reserved ASIDs looking for a match.
- * If we find one, then we can update our mm to use newasid
- * (i.e. the same ASID in the current generation) but we can't
- * exit the loop early, since we need to ensure that all copies
- * of the old ASID are updated to reflect the mm. Failure to do
- * so could result in us missing the reserved ASID in a future
- * generation.
- */
- for_each_possible_cpu(cpu) {
- if (reserved_asid(info, cpu) == asid) {
- hit = true;
- reserved_asid(info, cpu) = newasid;
- }
- }
-
- return hit;
-}
-
-static u64 new_context(struct asid_info *info, atomic64_t *pasid)
-{
- static u32 cur_idx = 1;
- u64 asid = atomic64_read(pasid);
- u64 generation = atomic64_read(&info->generation);
-
- if (asid != 0) {
- u64 newasid = generation | (asid & ~ASID_MASK(info));
-
- /*
- * If our current ASID was active during a rollover, we
- * can continue to use it and this was just a false alarm.
- */
- if (check_update_reserved_asid(info, asid, newasid))
- return newasid;
-
- /*
- * We had a valid ASID in a previous life, so try to re-use
- * it if possible.
- */
- if (!__test_and_set_bit(asid2idx(info, asid), info->map))
- return newasid;
- }
-
- /*
- * Allocate a free ASID. If we can't find one, take a note of the
- * currently active ASIDs and mark the TLBs as requiring flushes. We
- * always count from ASID #2 (index 1), as we use ASID #0 when setting
- * a reserved TTBR0 for the init_mm and we allocate ASIDs in even/odd
- * pairs.
- */
- asid = find_next_zero_bit(info->map, NUM_CTXT_ASIDS(info), cur_idx);
- if (asid != NUM_CTXT_ASIDS(info))
- goto set_asid;
-
- /* We're out of ASIDs, so increment the global generation count */
- generation = atomic64_add_return_relaxed(ASID_FIRST_VERSION(info),
- &info->generation);
- flush_context(info);
-
- /* We have more ASIDs than CPUs, so this will always succeed */
- asid = find_next_zero_bit(info->map, NUM_CTXT_ASIDS(info), 1);
-
-set_asid:
- __set_bit(asid, info->map);
- cur_idx = asid;
- return idx2asid(info, asid) | generation;
-}
-
-static void asid_new_context(struct asid_info *info, atomic64_t *pasid,
- unsigned int cpu);
-
-/*
- * Check the ASID is still valid for the context. If not generate a new ASID.
- *
- * @pasid: Pointer to the current ASID batch
- * @cpu: current CPU ID. Must have been acquired throught get_cpu()
- */
-static void asid_check_context(struct asid_info *info,
- atomic64_t *pasid, unsigned int cpu)
-{
- u64 asid, old_active_asid;
-
- asid = atomic64_read(pasid);
-
- /*
- * The memory ordering here is subtle.
- * If our active_asid is non-zero and the ASID matches the current
- * generation, then we update the active_asid entry with a relaxed
- * cmpxchg. Racing with a concurrent rollover means that either:
- *
- * - We get a zero back from the cmpxchg and end up waiting on the
- * lock. Taking the lock synchronises with the rollover and so
- * we are forced to see the updated generation.
- *
- * - We get a valid ASID back from the cmpxchg, which means the
- * relaxed xchg in flush_context will treat us as reserved
- * because atomic RmWs are totally ordered for a given location.
- */
- old_active_asid = atomic64_read(&active_asid(info, cpu));
- if (old_active_asid &&
- !((asid ^ atomic64_read(&info->generation)) >> info->bits) &&
- atomic64_cmpxchg_relaxed(&active_asid(info, cpu),
- old_active_asid, asid))
- return;
-
- asid_new_context(info, pasid, cpu);
-}
-
-/*
- * Generate a new ASID for the context.
- *
- * @pasid: Pointer to the current ASID batch allocated. It will be updated
- * with the new ASID batch.
- * @cpu: current CPU ID. Must have been acquired through get_cpu()
- */
-static void asid_new_context(struct asid_info *info, atomic64_t *pasid,
- unsigned int cpu)
-{
- unsigned long flags;
- u64 asid;
-
- raw_spin_lock_irqsave(&info->lock, flags);
- /* Check that our ASID belongs to the current generation. */
- asid = atomic64_read(pasid);
- if ((asid ^ atomic64_read(&info->generation)) >> info->bits) {
- asid = new_context(info, pasid);
- atomic64_set(pasid, asid);
- }
-
- if (cpumask_test_and_clear_cpu(cpu, &info->flush_pending))
- info->flush_cpu_ctxt_cb();
-
- atomic64_set(&active_asid(info, cpu), asid);
- raw_spin_unlock_irqrestore(&info->lock, flags);
-}
-
void check_and_switch_context(struct mm_struct *mm, unsigned int cpu)
{
if (system_supports_cnp())
@@ -305,38 +108,6 @@ static void asid_flush_cpu_ctxt(void)
local_flush_tlb_all();
}

-/*
- * Initialize the ASID allocator
- *
- * @info: Pointer to the asid allocator structure
- * @bits: Number of ASIDs available
- * @asid_per_ctxt: Number of ASIDs to allocate per-context. ASIDs are
- * allocated contiguously for a given context. This value should be a power of
- * 2.
- */
-static int asid_allocator_init(struct asid_info *info,
- u32 bits, unsigned int asid_per_ctxt,
- void (*flush_cpu_ctxt_cb)(void))
-{
- info->bits = bits;
- info->ctxt_shift = ilog2(asid_per_ctxt);
- info->flush_cpu_ctxt_cb = flush_cpu_ctxt_cb;
- /*
- * Expect allocation after rollover to fail if we don't have at least
- * one more ASID than CPUs. ASID #0 is always reserved.
- */
- WARN_ON(NUM_CTXT_ASIDS(info) - 1 <= num_possible_cpus());
- atomic64_set(&info->generation, ASID_FIRST_VERSION(info));
- info->map = kcalloc(BITS_TO_LONGS(NUM_CTXT_ASIDS(info)),
- sizeof(*info->map), GFP_KERNEL);
- if (!info->map)
- return -ENOMEM;
-
- raw_spin_lock_init(&info->lock);
-
- return 0;
-}
-
static int asids_init(void)
{
u32 bits = get_cpu_asid_bits();
@@ -344,7 +115,7 @@ static int asids_init(void)
if (!asid_allocator_init(&asid_info, bits, ASID_PER_CONTEXT,
asid_flush_cpu_ctxt))
panic("Unable to initialize ASID allocator for %lu ASIDs\n",
- 1UL << bits);
+ NUM_ASIDS(&asid_info));

asid_info.active = &active_asids;
asid_info.reserved = &reserved_asids;
--
2.11.0
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