powerpc: Add Initiate Coprocessor Store Word (icswx) support

Icswx is a PowerPC instruction to send data to a co-processor. On Book-S
processors the LPAR_ID and process ID (PID) of the owning process are
registered in the window context of the co-processor at initialization
time. When the icswx instruction is executed the L2 generates a cop-reg
transaction on PowerBus. The transaction has no address and the
processor does not perform an MMU access to authenticate the transaction.
The co-processor compares the LPAR_ID and the PID included in the
transaction and the LPAR_ID and PID held in the window context to
determine if the process is authorized to generate the transaction.

The OS needs to assign a 16-bit PID for the process. This cop-PID needs
to be updated during context switch. The cop-PID needs to be destroyed
when the context is destroyed.

Signed-off-by: Sonny Rao <sonnyrao@linux.vnet.ibm.com>
Signed-off-by: Tseng-Hui (Frank) Lin <thlin@linux.vnet.ibm.com>
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 211 insertions, 0 deletions

diff --git a/arch/powerpc/mm/mmu_context_hash64.c b/arch/powerpc/mm/mmu_context_hash64.c
index c5859448a0ab..c517815404c4 100644
--- a/arch/powerpc/mm/mmu_context_hash64.c
+++ b/arch/powerpc/mm/mmu_context_hash64.c
@@ -20,9 +20,205 @@
 #include <linux/idr.h>
 #include <linux/module.h>
 #include <linux/gfp.h>
+#include <linux/slab.h>
 
 #include <asm/mmu_context.h>
 
+#ifdef CONFIG_PPC_ICSWX
+/*
+ * The processor and its L2 cache cause the icswx instruction to
+ * generate a COP_REQ transaction on PowerBus. The transaction has
+ * no address, and the processor does not perform an MMU access
+ * to authenticate the transaction. The command portion of the
+ * PowerBus COP_REQ transaction includes the LPAR_ID (LPID) and
+ * the coprocessor Process ID (PID), which the coprocessor compares
+ * to the authorized LPID and PID held in the coprocessor, to determine
+ * if the process is authorized to generate the transaction.
+ * The data of the COP_REQ transaction is 128-byte or less and is
+ * placed in cacheable memory on a 128-byte cache line boundary.
+ *
+ * The task to use a coprocessor should use use_cop() to allocate
+ * a coprocessor PID before executing icswx instruction. use_cop()
+ * also enables the coprocessor context switching. Drop_cop() is
+ * used to free the coprocessor PID.
+ *
+ * Example:
+ * Host Fabric Interface (HFI) is a PowerPC network coprocessor.
+ * Each HFI have multiple windows. Each HFI window serves as a
+ * network device sending to and receiving from HFI network.
+ * HFI immediate send function uses icswx instruction. The immediate
+ * send function allows small (single cache-line) packets be sent
+ * without using the regular HFI send FIFO and doorbell, which are
+ * much slower than immediate send.
+ *
+ * For each task intending to use HFI immediate send, the HFI driver
+ * calls use_cop() to obtain a coprocessor PID for the task.
+ * The HFI driver then allocate a free HFI window and save the
+ * coprocessor PID to the HFI window to allow the task to use the
+ * HFI window.
+ *
+ * The HFI driver repeatedly creates immediate send packets and
+ * issues icswx instruction to send data through the HFI window.
+ * The HFI compares the coprocessor PID in the CPU PID register
+ * to the PID held in the HFI window to determine if the transaction
+ * is allowed.
+ *
+ * When the task to release the HFI window, the HFI driver calls
+ * drop_cop() to release the coprocessor PID.
+ */
+
+#define COP_PID_NONE 0
+#define COP_PID_MIN (COP_PID_NONE + 1)
+#define COP_PID_MAX (0xFFFF)
+
+static DEFINE_SPINLOCK(mmu_context_acop_lock);
+static DEFINE_IDA(cop_ida);
+
+void switch_cop(struct mm_struct *next)
+{
+        mtspr(SPRN_PID, next->context.cop_pid);
+        mtspr(SPRN_ACOP, next->context.acop);
+}
+
+static int new_cop_pid(struct ida *ida, int min_id, int max_id,
+                       spinlock_t *lock)
+{
+        int index;
+        int err;
+
+again:
+        if (!ida_pre_get(ida, GFP_KERNEL))
+                return -ENOMEM;
+
+        spin_lock(lock);
+        err = ida_get_new_above(ida, min_id, &index);
+        spin_unlock(lock);
+
+        if (err == -EAGAIN)
+                goto again;
+        else if (err)
+                return err;
+
+        if (index > max_id) {
+                spin_lock(lock);
+                ida_remove(ida, index);
+                spin_unlock(lock);
+                return -ENOMEM;
+        }
+
+        return index;
+}
+
+static void sync_cop(void *arg)
+{
+        struct mm_struct *mm = arg;
+
+        if (mm == current->active_mm)
+                switch_cop(current->active_mm);
+}
+
+/**
+ * Start using a coprocessor.
+ * @acop: mask of coprocessor to be used.
+ * @mm: The mm the coprocessor to associate with. Most likely current mm.
+ *
+ * Return a positive PID if successful. Negative errno otherwise.
+ * The returned PID will be fed to the coprocessor to determine if an
+ * icswx transaction is authenticated.
+ */
+int use_cop(unsigned long acop, struct mm_struct *mm)
+{
+        int ret;
+
+        if (!cpu_has_feature(CPU_FTR_ICSWX))
+                return -ENODEV;
+
+        if (!mm || !acop)
+                return -EINVAL;
+
+        /* We need to make sure mm_users doesn't change */
+        down_read(&mm->mmap_sem);
+        spin_lock(mm->context.cop_lockp);
+
+        if (mm->context.cop_pid == COP_PID_NONE) {
+                ret = new_cop_pid(&cop_ida, COP_PID_MIN, COP_PID_MAX,
+                                  &mmu_context_acop_lock);
+                if (ret < 0)
+                        goto out;
+
+                mm->context.cop_pid = ret;
+        }
+        mm->context.acop |= acop;
+
+        sync_cop(mm);
+
+        /*
+         * If this is a threaded process then there might be other threads
+         * running. We need to send an IPI to force them to pick up any
+         * change in PID and ACOP.
+         */
+        if (atomic_read(&mm->mm_users) > 1)
+                smp_call_function(sync_cop, mm, 1);
+
+        ret = mm->context.cop_pid;
+
+out:
+        spin_unlock(mm->context.cop_lockp);
+        up_read(&mm->mmap_sem);
+
+        return ret;
+}
+EXPORT_SYMBOL_GPL(use_cop);
+
+/**
+ * Stop using a coprocessor.
+ * @acop: mask of coprocessor to be stopped.
+ * @mm: The mm the coprocessor associated with.
+ */
+void drop_cop(unsigned long acop, struct mm_struct *mm)
+{
+        int free_pid = COP_PID_NONE;
+
+        if (!cpu_has_feature(CPU_FTR_ICSWX))
+                return;
+
+        if (WARN_ON_ONCE(!mm))
+                return;
+
+        /* We need to make sure mm_users doesn't change */
+        down_read(&mm->mmap_sem);
+        spin_lock(mm->context.cop_lockp);
+
+        mm->context.acop &= ~acop;
+
+        if ((!mm->context.acop) && (mm->context.cop_pid != COP_PID_NONE)) {
+                free_pid = mm->context.cop_pid;
+                mm->context.cop_pid = COP_PID_NONE;
+        }
+
+        sync_cop(mm);
+
+        /*
+         * If this is a threaded process then there might be other threads
+         * running. We need to send an IPI to force them to pick up any
+         * change in PID and ACOP.
+         */
+        if (atomic_read(&mm->mm_users) > 1)
+                smp_call_function(sync_cop, mm, 1);
+
+        if (free_pid != COP_PID_NONE) {
+                spin_lock(&mmu_context_acop_lock);
+                ida_remove(&cop_ida, free_pid);
+                spin_unlock(&mmu_context_acop_lock);
+        }
+
+        spin_unlock(mm->context.cop_lockp);
+        up_read(&mm->mmap_sem);
+}
+EXPORT_SYMBOL_GPL(drop_cop);
+
+#endif /* CONFIG_PPC_ICSWX */
+
 static DEFINE_SPINLOCK(mmu_context_lock);
 static DEFINE_IDA(mmu_context_ida);
 
@@ -78,6 +274,16 @@ int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
                 slice_set_user_psize(mm, mmu_virtual_psize);
         subpage_prot_init_new_context(mm);
         mm->context.id = index;
+#ifdef CONFIG_PPC_ICSWX
+        mm->context.cop_lockp = kmalloc(sizeof(spinlock_t), GFP_KERNEL);
+        if (!mm->context.cop_lockp) {
+                __destroy_context(index);
+                subpage_prot_free(mm);
+                mm->context.id = NO_CONTEXT;
+                return -ENOMEM;
+        }
+        spin_lock_init(mm->context.cop_lockp);
+#endif /* CONFIG_PPC_ICSWX */
 
         return 0;
 }
@@ -92,6 +298,11 @@ EXPORT_SYMBOL_GPL(__destroy_context);
 
 void destroy_context(struct mm_struct *mm)
 {
+#ifdef CONFIG_PPC_ICSWX
+        drop_cop(mm->context.acop, mm);
+        kfree(mm->context.cop_lockp);
+        mm->context.cop_lockp = NULL;
+#endif /* CONFIG_PPC_ICSWX */
         __destroy_context(mm->context.id);
         subpage_prot_free(mm);
         mm->context.id = MMU_NO_CONTEXT;