lkml.org 
[lkml]   [2019]   [Mar]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH RFC 13/14] arm/kvm: Introduce a new VMID allocator
Date
A follow-up patch will replace the KVM VMID allocator with the arm64 ASID
allocator. It is not yet clear how the code can be shared between arm
and arm64, so this is a verbatim copy of arch/arm64/lib/asid.c.

Signed-off-by: Julien Grall <julien.grall@arm.com>
---
arch/arm/include/asm/kvm_asid.h | 81 +++++++++++++++++
arch/arm/kvm/Makefile | 1 +
arch/arm/kvm/asid.c | 191 ++++++++++++++++++++++++++++++++++++++++
3 files changed, 273 insertions(+)
create mode 100644 arch/arm/include/asm/kvm_asid.h
create mode 100644 arch/arm/kvm/asid.c

diff --git a/arch/arm/include/asm/kvm_asid.h b/arch/arm/include/asm/kvm_asid.h
new file mode 100644
index 000000000000..f312a6d7543c
--- /dev/null
+++ b/arch/arm/include/asm/kvm_asid.h
@@ -0,0 +1,81 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ARM_KVM_ASID_H__
+#define __ARM_KVM_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);
+ /* Callback to call when a context is updated */
+ void (*update_ctxt_cb)(void *ctxt);
+};
+
+#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, void *ctxt);
+
+/*
+ * 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,
+ void *ctxt)
+{
+ 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, ctxt);
+}
+
+int asid_allocator_init(struct asid_info *info,
+ u32 bits, unsigned int asid_per_ctxt,
+ void (*flush_cpu_ctxt_cb)(void),
+ void (*update_ctxt_cb)(void *ctxt));
+
+#endif /* __ARM_KVM_ASID_H__ */
diff --git a/arch/arm/kvm/Makefile b/arch/arm/kvm/Makefile
index 531e59f5be9c..35d2d4c67827 100644
--- a/arch/arm/kvm/Makefile
+++ b/arch/arm/kvm/Makefile
@@ -21,6 +21,7 @@ obj-$(CONFIG_KVM_ARM_HOST) += hyp/

obj-y += kvm-arm.o init.o interrupts.o
obj-y += handle_exit.o guest.o emulate.o reset.o
+obj-y += asid.o
obj-y += coproc.o coproc_a15.o coproc_a7.o vgic-v3-coproc.o
obj-y += $(KVM)/arm/arm.o $(KVM)/arm/mmu.o $(KVM)/arm/mmio.o
obj-y += $(KVM)/arm/psci.o $(KVM)/arm/perf.o
diff --git a/arch/arm/kvm/asid.c b/arch/arm/kvm/asid.c
new file mode 100644
index 000000000000..60a25270163a
--- /dev/null
+++ b/arch/arm/kvm/asid.c
@@ -0,0 +1,191 @@
+// 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/kvm_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()
+ * @ctxt: Context to update when calling update_context
+ */
+void asid_new_context(struct asid_info *info, atomic64_t *pasid,
+ unsigned int cpu, void *ctxt)
+{
+ 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);
+
+ info->update_ctxt_cb(ctxt);
+
+ 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),
+ void (*update_ctxt_cb)(void *ctxt))
+{
+ info->bits = bits;
+ info->ctxt_shift = ilog2(asid_per_ctxt);
+ info->flush_cpu_ctxt_cb = flush_cpu_ctxt_cb;
+ info->update_ctxt_cb = update_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;
+}
--
2.11.0
\
 
 \ /
  Last update: 2019-03-21 17:37    [W:0.134 / U:46.720 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site